**Properties of Basalt Plastics and of Composites Reinforced by Hybrid Fibers in Operating Conditions**

N.M. Chikhradze, L.A. Japaridze and G.S. Abashidze

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/48289

## **1. Introduction**

242 Composites and Their Applications

*Environment*:1-8.

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Wan Rosli, W. D., K. N. Law, Z. Zainuddin, and R. Asro. 2004. Effect of pulping variables on the characteristics of oil-palm frond-fiber. *Bioresource Technology* 93 (3):233-240. Wong, K. J., U. Nirmal, and B. K. Lim. 2010. Impact behavior of short and continuous fiberreinforced polyester composites. *Journal of Reinforced Plastics and Composites* 29 (23):3463-

Xiao, B., X. F. Sun, and R. Sun. 2001. Chemical modification of lignins with succinic anhydride in aqueous systems. *Polymer Degradation and Stability* 71 (2):223-231. Yatim, J.M., Abd Khalid, N.H, Reza. 2011. Seminar Embracing Green Technology In Construction – Way Forward., 26th April, Grand Margherita Hotel, Kuching Sarawak,

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Zulkifli, R., M. J. M. Nor, A. R. Ismail, M. Z. Nuawi, S. Abdullah, M. F. M. Tahir, and M. N. A. Rahman. 2009. Comparison of acoustic properties between coir fibre and oil palm

fibre. *European Journal of Scientific Research* 33 (1):144-152.

Polymeric reinforced materials are characterized by a number of advantages over traditional structural materials since they offer such unique properties as high specific strength in some cases, in combination with light transmission, radio transparency, high electrical insulating characteristics, non-magnetic properties, corrosion resistance.

The possibility of the preparation of new materials with predetermined characteristics is one of the main advantages of reinforced plastics. In Table 1 the standard mechanical characteristics of the most abundant structural materials as well as averaged standard characteristics, for example, of oriented and randomly reinforced glass-plastics are given.

In recent years an information on new type of polymeric composite-basalt plastic (BP), in which the basalt fiber is used instead of glass reinforcing one [1,2], is of frequent occurrence. Basalt fibers are practically highly competitive with glass ones by main mechanical characteristics and surpasses them by some of them, in particular, by water-resistance and chemical stability (is shown below). But in the form of twisted and non-twisted threads, rovings, roving cloth and discrete fibers, basalt ones represent an alternative and promising reinforcing element for composites. In addition, at solving of a series of specific problems, for example, for preparation of materials with predetermined strength and deformation characteristics in different directions of load application, the combination of glass, highstrength basalt, high-strength and high-modulus carbon fibers were used, that is to say, the production of composites, reinforced by hybrid fibers (HFRC) was organized [3-8].

Here we don't detail the properties of these and other types of reinforcing fibers. We have restricted ourselves to the comparison of glass, basalt and carbon fibers (Table 2).

© 2012 Chikhradze et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Chikhradze et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Properties of Basalt Plastics and of Composites Reinforced by Hybrid Fibers in Operating Conditions 245

presence of polymeric matrix in considered materials predetermines an impossibility of the evaluation of strength or deformability at room temperature without specifying of

 Directional locating of reinforcing fibers in the plane of reinforcement as well as a lamination of the structure in the direction perpendicular to mentioned plane, causes an anisotropy of mechanical and other properties. As a rule, a number of characteristics, necessary for determination of one or another properties of reinforced plastics, is considerably more than for isotropic materials. Moreover, the regularities of the behavior of reinforced plastics at mechanical testing depend on the direction of load application. For example, for oriented composites a tension diagram in the direction of reinforcement is governed by Hooke's law. At loading at an angle to the direction of reinforcement, this diagram becomes essentially non-linear. A lamination of the structure of polymeric composites predetermines their low resistance to interlayer shear and to transverse breaking off. Therefore, at bending, these materials may be destroyed because of the fact that tangential stresses will be higher than material's resistance to interlayer shear instead of the fact that normal stresses (extending or compressing) may

 Deformations, generated perpendicularly to reinforcing fibers, are mainly realized in matrix interlayers because of low rigidity of the latter in comparison with glass, basalt or carbon fibers; this fact leads to the formation of the cracks in the interlayers of a binder between the fibers or at phase boundaries. Low crack resistance is particularly characteristic of oriented plastics. The cracks have little or no effect on the values of characteristics, obtained as a result of short-term testing. However, such characteristics of a material as hermeticity, resistance to corrosive media, mechanical and electrotechnical properties in the conditions of long-term operation at the appearance and intergrowth of

 Relatively low value of elasticity modulus of reinforced plastics and composites leads to the fact that load-carrying ability of thin-wall structures is limited by deformability and stability instead of the strength. For complete use of high strength characteristics of the composites it is profitable to design the item and structure as three-layered or to provide the stiffening ribs. Designing must be carried out in such a way as to the material will operate on tension instead of compression, whenever possible. However, it should be noted that in some cases the low elasticity modulus is a definite advantage of reinforced polymers (for example, pipe-lines from mentioned materials without the

Considered peculiarities of reinforced polymers, generally, and of BP and HFRC, in particular, must be taken into account at designing and at the use of structures and items

Appearance of new generation of reinforced polymers – BP and HFRC is due to the quest for preparation of the materials, characterized by higher initial mechanical and other indexes and by higher stability of these indexes at the action of various operating factors.

time in the course of which the materials are in stressed state.

attain the limiting values.

the track are significantly impaired.

from mentioned materials.

compensators of temperature deformation and etc.)

**Table 1.** Mechanical properties of structural materials


Remark: Indexes are given for the production of the firms of various countries.

**Table 2.** Properties of reinforcing fibers

In parallel with the advantages, BP and HFRC, undoubtedly, are characterized by some disadvantages, which must be taken into account at the preparation and operation of structures and items with the use of BP and HFRC. These disadvantages involve:


presence of polymeric matrix in considered materials predetermines an impossibility of the evaluation of strength or deformability at room temperature without specifying of time in the course of which the materials are in stressed state.

244 Composites and Their Applications

**Metals**  Steel

Titanium

**Wood** 

**Plastics**  Polyethylene Vinyl plastic **Glass reinforced** 

**plastics**  Unidirectional Glass-cloth-base

laminate Randomly oriented

Aluminum alloy

Material Density

Kg.m-3

7800 2800 4500

960 1400

2000

1900

1400

gr. m-3

Remark: Indexes are given for the production of the firms of various countries.

**Table 1.** Mechanical properties of structural materials

Fiber Density

**Table 2.** Properties of reinforcing fibers

testing the dissipation increased.

Tensile strength, MPa

> 400 300 350

> > 20 60

1600

500

100

Failure stress, GPa

In parallel with the advantages, BP and HFRC, undoubtedly, are characterized by some disadvantages, which must be taken into account at the preparation and operation of

 Structural non-uniformity and inadequate stability of the technology of preparation leads to considerable dissipation of mechanical and other indexes, which may attain to 15-20% in relation to average values even at standard short-term testing. At long-term

 Polymeric nature of a matrix determines an enhanced sensitivity of materials to the prehistory of preparation and to temperature-time regime of further operation, which is responsible for determines strength and deformation properties of BP and HFRC. At moderate temperatures for traditional structural materials a temperature-time dependence of mechanical and other properties appears only slightly, whereas the

structures and items with the use of BP and HFRC. These disadvantages involve:

Glass 2.4-2.5 2.8-3.0 4.7-5.6 74-95 Basalt 2.6-2.8 1.9-2.6 3.5-4.5 70-90 Carbon 1.9-2.1 2.2-7.2 0.5-2.4 200-785

Oak 720 130 15 15.2 1750

Tensile modulus, GPa

> 200 72 115

0.5 3

56

30

8

Specific strength km

> 5.1 10.7 17.8

> > 2.1 4.3

80.0

26.2

6.7

Extension at failure, %

Specific rigidity km

> 2560 2580 2560

> > 52 210

2800

1570

530

Elasticity modulus GPa


Considered peculiarities of reinforced polymers, generally, and of BP and HFRC, in particular, must be taken into account at designing and at the use of structures and items from mentioned materials.

Appearance of new generation of reinforced polymers – BP and HFRC is due to the quest for preparation of the materials, characterized by higher initial mechanical and other indexes and by higher stability of these indexes at the action of various operating factors.

At the present time the volumes of the production and of the use of the composites, reinforced by high-strength and high-modulus fibers, are insignificant. The main consumers of mentioned materials are aviation and rocket-space engineering. The main barrier for widening of the fields of the use of such materials (for example, in wind power engineering, chemical production and etc.) is their high cost.

Properties of Basalt Plastics and of Composites Reinforced by Hybrid Fibers in Operating Conditions 247

determined by well-known three sigma rule by calculation of arithmetic mean and by rootmean-square deviation of the strength, which are defined on the basis of statistical analysis

Calculated resistances of the materials, operating at the joint action of static load and regimes, different from normal ones (elevated temperature, high humidity, corrosive medium and etc.) were determined by multiplying the long-term calculated resistances into

,, , *<sup>T</sup> <sup>w</sup> cor atm R RK R RK R RK R RK c cT c c w c c cor c c atm*

where *K*T, *K*w, *K*cor, *K*atm - coefficients of operating conditions of composites, service of which is provided, respectively, at elevated temperature, in water or at high humidity at the action of corrosive media, in atmospheric conditions, as well as at synchronous long-term action of load as well as of external factors. In some cases the coefficients of operating conditions were determined at the joint action of various factors, for example, of temperature, water

**BP-1.** Sheet basalt plastic. Thickness (δ)-1.5-2.5mm; density (ρ)-1360-1380 kg.m-3; Matrix – unsaturated polyester resin of Turkish production (65 mass%). Reinforcing element – chopped fiber, obtained by cutting of basalt roving of Georgian production with following characteristics: rectilinear density 600-4800 tex; elemental fiber diameter 10-16 μ; specific

**BP-2.** Basalt cloth – based laminate. δ = 0.7-5.0 mm; ρ = 1530-1560 kg.m-3 . Matrix-phenolformaldehyde resin of Ukrainian production (25-35 mass%). Reinforcing element – cloth from twisted threads of Georgian production with following characteristics: thickness 0.25- 0.35 mm; surface density 150-450 g/m2; density in warp 4-8 th/cm; density in weft 6-12 th/cm, or cloth from basalt roving with the indexes: thickness 0.4-0.9 mm; surface density

The mode of preparation: direct pressing, pressure 45-55 kgf/cm2, pressing temperature 413-

Expected field of application: shells of three–layered building panels (among them for

**BP-3.** Oriented basalt plastic. δ = 1.0-7.0 mm; ρ = 1520-1540 kg.m-3. Matrix-epoxy-phenol resin of Ukrainian production (25-32 mass%). Reinforcing element-permanently oriented

The mode of preparation: contact moulding (without pressure and temperature).

Expected field of application: light-transparent guarding building structure.

300-700 g/m2; density in warp – 1.7-3.5 th/cm; density in weft 2.9-4.0 th/cm;

of the results of mass testing of strength properties of BP and HFRC.

corresponding coefficients of operating conditions:

/humidity (*K*T,w).

The objects of investigations were:

**2.1. Basalt reinforced plastics** 

443K, holding time on 1 mm-5-12 min.

basalt fiber in the form of roving (data see in BP-1).

corrosive media).

tenacity 350-450 mN/tex.

In regard to the cost of BP and HFRC, it should be noted that the ways for their cost reduction, probably, are associated with a cheapening of initial materials as well as of mechanization of the production instead of the increase of the output, concentration and specialization of the production. In this connection, the problem of the cost reduction for composites by, if only for, partial replacement of expense and scarce carbon fiber by considerably cheaper (by an order) basalt one without significant impairment of main operating properties of the material is highly topical. Moreover, the share of reinforcing fibers as well as of a binder in the expenses of raw materials is distinct for the composites of various types. For the composites, in which the nonwoven reinforcing elements are used in the form of threads and mats, the expenses of reinforcing materials attain to 30-35% of all material expenses. At the same time the expenses of reinforcing materials in the form of the cloths may attain to 50-70% at the preparation of basalt plastics. Therefore an essential effect in the reduction of composite's cost may be attained by replacing of the cloths from twisted threads by nonwoven reinforcing materials and roving cloths.

Price cost reduction for BP and HFRC is also possible at the expense of introducing of efficient fillers-reinforcers into the matrix composition. This method allows a considerable decrease of fiber content without an essential reduction of characteristics of the resulting material.

One more way for enhancement of the efficiency of the use of BP and HFRC in action is a rational design and the use of the items from them with regard to the effect of real environment on the material. Below the primary attention is given to more or less detailed consideration of these problems.

## **2. General methodology of investigations**

At designing of structures and items from composite materials, primarily the values of their calculated resistances are necessary. By long-term calculated resistance (Rcl) of the material in normal conditions the product of normative resistance of the material by coefficient of longterm resistance and by coefficient of the uniformity of its mechanical characteristics is meant:

#### *R*cl=*R*nor*K*ℓ-t *K*<sup>u</sup>

Normative resistance (*R*nor) was determined a strength limit of the materials under study by the results of short-term testing of small samples, carried out in accordance with acting standards. Coefficient of long-term resistance (*K*ℓ-t) was determined by testing to failure of the series of the samples of the materials at long-term loading at the stresses comprising a definite part from a strength limit of the material. Uniformity coefficient (*K*u) was determined by well-known three sigma rule by calculation of arithmetic mean and by rootmean-square deviation of the strength, which are defined on the basis of statistical analysis of the results of mass testing of strength properties of BP and HFRC.

Calculated resistances of the materials, operating at the joint action of static load and regimes, different from normal ones (elevated temperature, high humidity, corrosive medium and etc.) were determined by multiplying the long-term calculated resistances into corresponding coefficients of operating conditions:

$$R\_{c\ell}^T = R\_{c\ell} \cdot K\_{T'} \qquad \qquad R\_{c\ell}^w = R\_{c\ell} \cdot K\_{w\prime} \qquad \qquad R\_{c\ell}^{cor} = R\_{c\ell} \cdot K\_{cor\prime} \qquad \qquad R\_{c\ell}^{atm} = R\_{c\ell} \cdot K\_{atm}$$

where *K*T, *K*w, *K*cor, *K*atm - coefficients of operating conditions of composites, service of which is provided, respectively, at elevated temperature, in water or at high humidity at the action of corrosive media, in atmospheric conditions, as well as at synchronous long-term action of load as well as of external factors. In some cases the coefficients of operating conditions were determined at the joint action of various factors, for example, of temperature, water /humidity (*K*T,w).

The objects of investigations were:

246 Composites and Their Applications

material.

consideration of these problems.

**2. General methodology of investigations** 

chemical production and etc.) is their high cost.

threads by nonwoven reinforcing materials and roving cloths.

At the present time the volumes of the production and of the use of the composites, reinforced by high-strength and high-modulus fibers, are insignificant. The main consumers of mentioned materials are aviation and rocket-space engineering. The main barrier for widening of the fields of the use of such materials (for example, in wind power engineering,

In regard to the cost of BP and HFRC, it should be noted that the ways for their cost reduction, probably, are associated with a cheapening of initial materials as well as of mechanization of the production instead of the increase of the output, concentration and specialization of the production. In this connection, the problem of the cost reduction for composites by, if only for, partial replacement of expense and scarce carbon fiber by considerably cheaper (by an order) basalt one without significant impairment of main operating properties of the material is highly topical. Moreover, the share of reinforcing fibers as well as of a binder in the expenses of raw materials is distinct for the composites of various types. For the composites, in which the nonwoven reinforcing elements are used in the form of threads and mats, the expenses of reinforcing materials attain to 30-35% of all material expenses. At the same time the expenses of reinforcing materials in the form of the cloths may attain to 50-70% at the preparation of basalt plastics. Therefore an essential effect in the reduction of composite's cost may be attained by replacing of the cloths from twisted

Price cost reduction for BP and HFRC is also possible at the expense of introducing of efficient fillers-reinforcers into the matrix composition. This method allows a considerable decrease of fiber content without an essential reduction of characteristics of the resulting

One more way for enhancement of the efficiency of the use of BP and HFRC in action is a rational design and the use of the items from them with regard to the effect of real environment on the material. Below the primary attention is given to more or less detailed

At designing of structures and items from composite materials, primarily the values of their calculated resistances are necessary. By long-term calculated resistance (Rcl) of the material in normal conditions the product of normative resistance of the material by coefficient of longterm resistance and by coefficient of the uniformity of its mechanical characteristics is meant:

*R*cl=*R*nor*K*ℓ-t *K*<sup>u</sup> Normative resistance (*R*nor) was determined a strength limit of the materials under study by the results of short-term testing of small samples, carried out in accordance with acting standards. Coefficient of long-term resistance (*K*ℓ-t) was determined by testing to failure of the series of the samples of the materials at long-term loading at the stresses comprising a definite part from a strength limit of the material. Uniformity coefficient (*K*u) was

## **2.1. Basalt reinforced plastics**

**BP-1.** Sheet basalt plastic. Thickness (δ)-1.5-2.5mm; density (ρ)-1360-1380 kg.m-3; Matrix – unsaturated polyester resin of Turkish production (65 mass%). Reinforcing element – chopped fiber, obtained by cutting of basalt roving of Georgian production with following characteristics: rectilinear density 600-4800 tex; elemental fiber diameter 10-16 μ; specific tenacity 350-450 mN/tex.

The mode of preparation: contact moulding (without pressure and temperature).

Expected field of application: light-transparent guarding building structure.

**BP-2.** Basalt cloth – based laminate. δ = 0.7-5.0 mm; ρ = 1530-1560 kg.m-3 . Matrix-phenolformaldehyde resin of Ukrainian production (25-35 mass%). Reinforcing element – cloth from twisted threads of Georgian production with following characteristics: thickness 0.25- 0.35 mm; surface density 150-450 g/m2; density in warp 4-8 th/cm; density in weft 6-12 th/cm, or cloth from basalt roving with the indexes: thickness 0.4-0.9 mm; surface density 300-700 g/m2; density in warp – 1.7-3.5 th/cm; density in weft 2.9-4.0 th/cm;

The mode of preparation: direct pressing, pressure 45-55 kgf/cm2, pressing temperature 413- 443K, holding time on 1 mm-5-12 min.

Expected field of application: shells of three–layered building panels (among them for corrosive media).

**BP-3.** Oriented basalt plastic. δ = 1.0-7.0 mm; ρ = 1520-1540 kg.m-3. Matrix-epoxy-phenol resin of Ukrainian production (25-32 mass%). Reinforcing element-permanently oriented basalt fiber in the form of roving (data see in BP-1).

The mode of preparation: production of veneer, its impregnation by a binder, direct pressing of semifinished item.

Properties of Basalt Plastics and of Composites Reinforced by Hybrid Fibers in Operating Conditions 249

that these effects may exert some influence not only to the variation of absolute values of mechanical properties of BP and HFRC, but, to some extent, they may reflect on the indexes of uniformity of strength properties of the materials. To check this suggestion the investigations were carried out to reveal the influence of preliminary action on the indexes of uniformity of strength properties of BP-1, BP-2, HFRC-2 and HFRC-4 at tension. In Table 4 the results of these testing are given. They involve the data necessary to calculate the uniformity coefficient (number of testing – n, arithmetic – mean value for strength - σav, mean square deviation - σ´ as well as variation coefficient – V). The regimes of preliminary action on the samples of the material were: №1 – holding in laboratory room; №2 – heating at 353K over 10 days; №3 – steeping over 1 day; №4 - steeping over 10 days; №5 – steeping

over 10 days by further drying over 10 days; №6 - steeping over 10 days at 353K.

terms "long-term resistance" and "durability" an equal meaning is assigned.

As is seen from Table 4, the variation of Ku is relatively small and maximum reduction of Ku comprises 9 % for BP and 6 % for HFRC. Hence, the value of Ku, obtained by testing in normal temperature- humid conditions, may be used by confidence at practical calculations. Under prolonged (long-term) strength of the solid the dependence of time duration up to its failure on the stress and temperature is meant. The coefficient of long-term resistance is a value, determined by testing of a series of the materials samples under prolonged loading to failure at the stresses, constituent a definite part from material strength limit. Thus, in the

**Figure 1.** Structure of composite intended for shell

**Figure 2.** Structure of composite intended for spar

Expected field of application- auxiliary structural elements and details.

**BP-4.** Pressed basalt plastic. δ = 2.0-8.0 mm; ρ = 1850-1950 kg.m-3. Matrix – modified phenolformaldehyde resin of Ukrainian production (25-35 mass%). Reinforcing element-chopped or permanently oriented basalt fiber (data see in BP-1, BP-2).

The mode of preparation: preliminary impregnation of reinforcing element, direct pressing at the temperatures of 140-1600C; pressure 250-350 kgf/cm2, holding time 2-5 min on 1 mm of material.

Expected field of application: auxiliary structural details for corrosive media.

## **2.2. Composites on the basis of hybrid fibers**

**HFRC-1** . Oriented bi-directional composite. δ = 1.5-2.5 mm; ρ = 1450-1550 kg.m-3. Matrix – epoxy resin of Ukrainian production (70-75 mass%). Reinforcing elements – glass and carbon fibers (GF, CF), located in the composite by the scheme, presented in Fig.1. Glass fibers of alkalineless composition are presented in the form of roving of Ukrainian production. Polyacrylonitrile carbon rovings of Russian production offer the strength 2.3 GPa and elasticity modulus 220 GPa. Ratio GF : CF = 0.3÷0.7 (by mass).

The mode of preparation: production of prepreg, its direct pressing.

Expected field of application: shell of wind turbine blade.

**HFRC-2**. The same, but 20% of carbon fiber is replaced by basalt one in the form of roving.

**HFRC-3.** Oriented composite. δ = 2-3 mm, ρ = 1450-1550 kg.m-3. Matrix – the same as in the case of HFRC-1 and HFRC-2; Reinforcing elements – the same as in the case of HFRC-1 and HFRC-2 . They are located by the scheme, shown in fig. 2.

The mode of preparation: the same as in the case of HFRC-1 and HFRC-2.

Expected field of application: the spar of wind turbine blade.

**HFRC-4.** The material similar to the composite HFRC–3, but 20% of carbon fiber is replaced by basalt one in the form of roving.

The results of determination of normative resistances at various types of stressed state (tension, bending, compressing, shear - ,,, *t b c sh R R RR nor nor nor nor* as well as of short-term elasticity modulus at tension, bending and compressing ( , , *t bc st st st E EE* ) and coefficients of uniformity of strength properties of the materials under study are given in Table 3.

Returning to the problem on uniformity coefficient of material, it should be noted that testing, carried out for its determination were performed at room temperature – humid conditions. Incidentally, in the course of operating of the structures by the use of plastic materials, they may undergo to various temperature- humid effects and it may be suggested

**Figure 2.** Structure of composite intended for spar

material.

pressing of semifinished item.

The mode of preparation: production of veneer, its impregnation by a binder, direct

**BP-4.** Pressed basalt plastic. δ = 2.0-8.0 mm; ρ = 1850-1950 kg.m-3. Matrix – modified phenolformaldehyde resin of Ukrainian production (25-35 mass%). Reinforcing element-chopped

The mode of preparation: preliminary impregnation of reinforcing element, direct pressing at the temperatures of 140-1600C; pressure 250-350 kgf/cm2, holding time 2-5 min on 1 mm of

**HFRC-1** . Oriented bi-directional composite. δ = 1.5-2.5 mm; ρ = 1450-1550 kg.m-3. Matrix – epoxy resin of Ukrainian production (70-75 mass%). Reinforcing elements – glass and carbon fibers (GF, CF), located in the composite by the scheme, presented in Fig.1. Glass fibers of alkalineless composition are presented in the form of roving of Ukrainian production. Polyacrylonitrile carbon rovings of Russian production offer the strength 2.3

**HFRC-2**. The same, but 20% of carbon fiber is replaced by basalt one in the form of roving.

**HFRC-3.** Oriented composite. δ = 2-3 mm, ρ = 1450-1550 kg.m-3. Matrix – the same as in the case of HFRC-1 and HFRC-2; Reinforcing elements – the same as in the case of HFRC-1 and

**HFRC-4.** The material similar to the composite HFRC–3, but 20% of carbon fiber is replaced

The results of determination of normative resistances at various types of stressed state (tension, bending, compressing, shear - ,,, *t b c sh R R RR nor nor nor nor* as well as of short-term

Returning to the problem on uniformity coefficient of material, it should be noted that testing, carried out for its determination were performed at room temperature – humid conditions. Incidentally, in the course of operating of the structures by the use of plastic materials, they may undergo to various temperature- humid effects and it may be suggested

uniformity of strength properties of the materials under study are given in Table 3.

*st st st E EE* ) and coefficients of

Expected field of application- auxiliary structural elements and details.

Expected field of application: auxiliary structural details for corrosive media.

GPa and elasticity modulus 220 GPa. Ratio GF : CF = 0.3÷0.7 (by mass).

The mode of preparation: the same as in the case of HFRC-1 and HFRC-2.

elasticity modulus at tension, bending and compressing ( , , *t bc*

The mode of preparation: production of prepreg, its direct pressing.

Expected field of application: shell of wind turbine blade.

HFRC-2 . They are located by the scheme, shown in fig. 2.

Expected field of application: the spar of wind turbine blade.

by basalt one in the form of roving.

or permanently oriented basalt fiber (data see in BP-1, BP-2).

**2.2. Composites on the basis of hybrid fibers** 

that these effects may exert some influence not only to the variation of absolute values of mechanical properties of BP and HFRC, but, to some extent, they may reflect on the indexes of uniformity of strength properties of the materials. To check this suggestion the investigations were carried out to reveal the influence of preliminary action on the indexes of uniformity of strength properties of BP-1, BP-2, HFRC-2 and HFRC-4 at tension. In Table 4 the results of these testing are given. They involve the data necessary to calculate the uniformity coefficient (number of testing – n, arithmetic – mean value for strength - σav, mean square deviation - σ´ as well as variation coefficient – V). The regimes of preliminary action on the samples of the material were: №1 – holding in laboratory room; №2 – heating at 353K over 10 days; №3 – steeping over 1 day; №4 - steeping over 10 days; №5 – steeping over 10 days by further drying over 10 days; №6 - steeping over 10 days at 353K.

As is seen from Table 4, the variation of Ku is relatively small and maximum reduction of Ku comprises 9 % for BP and 6 % for HFRC. Hence, the value of Ku, obtained by testing in normal temperature- humid conditions, may be used by confidence at practical calculations.

Under prolonged (long-term) strength of the solid the dependence of time duration up to its failure on the stress and temperature is meant. The coefficient of long-term resistance is a value, determined by testing of a series of the materials samples under prolonged loading to failure at the stresses, constituent a definite part from material strength limit. Thus, in the terms "long-term resistance" and "durability" an equal meaning is assigned.


Properties of Basalt Plastics and of Composites Reinforced by Hybrid Fibers in Operating Conditions 251

(1)

The equation of temperature-time dependence of the solids, as it well known, relates

<sup>0</sup> exp

material destruction; *k* – Boltzmann's constant; *γ* - average coefficient of overstresses.

0

*U kT* 

where τo - is a constant, approximately equal to 10-13 sec, which in order of a value is near to the period of thermal oscillations of atoms; *U*0 – initial activation energy of the process of

Physical meaning of the formula (1) may be explained by means of thermal fluctuation theory of strength. According to this theory, destruction is kinetic, thermally fluctuating process of permanent accumulation of damages, developed in the body since the load application to its destruction. Breaking of interatomic bonds, activated by applied stress, is

In the course of experiments it has been established that BP and HFRC under our study are, mainly, obey the temperature-time dependence. Along with it, it should be noted, that in relation to BP and HFRC, which are bi or more component composites, physical meaning of the values τo, *U*0 and γ is not reasonably evident. But it should be taken into account that the main goal of our investigations is to obtain the empirical relationships between long-term resistance (durability) of new types of structural materials and the conditions of their operation. In this case the question about physical meaning of above-mentioned values does

0

  0

(2)

(3)

lg lg *kT <sup>U</sup> e*

*const* we obtain

*U*0 

 *BT* 

Thus, the linear dependence between material strength and temperature at τ = const is in existence. At elevating of testing temperature, primarily, the adhesion bonds are broken at the boundaries of basalt (glass) – binder and in the matrix the cracks, parallel to the fiber, are formed, since U0 values for silicate fibers are equal to 350-385 kJ/mole and the values of activation energy of destruction of polymeric matrix comprise 125-190 kJ/mole. Intensity of breaking of adhesion bond: carbon-binder is of lesser importance, since U0 for

durability (*τ*), stress (σ) and temperature (*T*) to each other [9,10]:

an elementary act of destruction process.

not need to be posed.

where <sup>0</sup>

*B*

lg

*<sup>i</sup> K*

lg

*e*

From (1) the following is obtained:

If in formula (2) it is granted that , *<sup>i</sup>*

 

Remark: 1 BP-1. Resistances at shear are given in the direction, perpendicular to sheet plane.

2. BP-2. For efforts acting in the direction of the base of basalt cloth (δ=7mm).

3. BP-3. At the ratio between longitudinal and transverse fibers, equal to 1:1 for efforts, acting in the direction of fibers. 4. BP-4. In numerator and denominator at reinforcing by chopped and oriented fibers, respectively.

5. HFRC-1, HFRC-2, HFRC-3, HFRC-4. In numerator and denominator the values along and transversely to X axis, respectively (Fig. 1,2).

**Table 3.** Normative resistances, short-term elasticity modulus and uniformity coefficients for BP and HFRC


**Table 4.** Statistical processing of the result of testing to reveal the influence of preliminary action of various factors on uniformity indexes.

The equation of temperature-time dependence of the solids, as it well known, relates durability (*τ*), stress (σ) and temperature (*T*) to each other [9,10]:

$$
\tau = \tau\_0 \exp\left(\frac{\mathcal{U}\_0 - \mathcal{\chi}\sigma}{kT}\right) \tag{1}
$$

where τo - is a constant, approximately equal to 10-13 sec, which in order of a value is near to the period of thermal oscillations of atoms; *U*0 – initial activation energy of the process of material destruction; *k* – Boltzmann's constant; *γ* - average coefficient of overstresses.

Physical meaning of the formula (1) may be explained by means of thermal fluctuation theory of strength. According to this theory, destruction is kinetic, thermally fluctuating process of permanent accumulation of damages, developed in the body since the load application to its destruction. Breaking of interatomic bonds, activated by applied stress, is an elementary act of destruction process.

In the course of experiments it has been established that BP and HFRC under our study are, mainly, obey the temperature-time dependence. Along with it, it should be noted, that in relation to BP and HFRC, which are bi or more component composites, physical meaning of the values τo, *U*0 and γ is not reasonably evident. But it should be taken into account that the main goal of our investigations is to obtain the empirical relationships between long-term resistance (durability) of new types of structural materials and the conditions of their operation. In this case the question about physical meaning of above-mentioned values does not need to be posed.

From (1) the following is obtained:

$$
\sigma = \frac{\mathcal{U}\_0 - \frac{kT}{\lg e} \lg \frac{\tau}{\tau\_0}}{\gamma} \tag{2}
$$

If in formula (2) it is granted that , *<sup>i</sup> const* we obtain

$$
\sigma = \frac{\mathcal{U}\_0}{\mathcal{Y}} - BT \tag{3}
$$

where <sup>0</sup> lg lg *<sup>i</sup> K B e* 

250 Composites and Their Applications

*<sup>t</sup> Rnor* , MPa

69.0 250.8 480.6 85.0 560.0

195.6 163.1 292.5 228.2 455.4 6.9

132.2 85.6

*<sup>b</sup> Rnor* , MPa

145.0 130.0 750.8 130.0 260.0

480.2 270.3 567.2 351.4 718.1 19.9

415.7 95.9

*<sup>c</sup> Rnor* , MPa

105.6 105.5 410.2 110.0 210.5

261.1 219.1 410.2 319.9 420.8 8.0

160.2 107.7

Remark: 1 BP-1. Resistances at shear are given in the direction, perpendicular to sheet plane.

4. BP-4. In numerator and denominator at reinforcing by chopped and oriented fibers, respectively.

V, %

11.1 12.0 12.3 11.3 10.6 13.0

> 7.8 8.6 8.2 7.9 7.9 8.3

2. BP-2. For efforts acting in the direction of the base of basalt cloth (δ=7mm).

 ' , MPa

*sh Rnor* , MPa

55.0 75.0 190.0 -

10.2 8.1 12.2 10.2 24.8 1.2

> 8.8 2.4

3. BP-3. At the ratio between longitudinal and transverse fibers, equal to 1:1 for efforts, acting in the direction of fibers.

**Table 3.** Normative resistances, short-term elasticity modulus and uniformity coefficients for BP and HFRC

Ku Material

HFRC-2

HFRC-4

(δ=0.8mm)

(δ=1.5mm)

5. HFRC-1, HFRC-2, HFRC-3, HFRC-4. In numerator and denominator the values along and transversely to X axis,

0.67 0.64 0.63 0.66 0.68 0.61

0.77 0.74 0.72 0.80 0.76 0.74

**Table 4.** Statistical processing of the result of testing to reveal the influence of preliminary action of

*t s t E* , GPa

6.0 26.0 31.5 19.3 19.5

9.4 3.9 15.0 5.4 96.9 5.8

49.7 19.8

> Act. reg.

№1 №2 №3 №4 №5 №6

№1 №2 №3 №4 №5 №6

*b s t E* , GPa

> - - - -

14.5 3.4 23.4 5.4 78.6 5.2

58.8 16.4

n σav, MPa

 ' , MPa

*c s t E* , GPa

> - - - -

10.6 4.2 14.6 5.8 78.1 4.1

51.0

16.7 0.70

V, %

9.9 9.5 10.5 10.2 10.7 10.8

6.5 10.8 9.6 10.4 10.0 10.8 Ku

0.70 0.71 0.69 0.69 0.68 0.68

0.80 0.67 0.71 0.69 0.70 0.68

Ku

0.65 0.78 0.75 0.75

0.72

0.68

0.74

Material

BP - 1 BP - 2 BP - 3 BP - 4

HFRC-1

HFRC-2

HFRC-3

HFRC-4

respectively (Fig. 1,2).

Act. reg.

№1 №2 №3 №4 №5 №6

№1 №2 №3 №4 №5 №6 n σav, MPa

various factors on uniformity indexes.

Material

BP-1

BP-2

(δ=0.8mm)

(δ=1.5mm)

Thus, the linear dependence between material strength and temperature at τ = const is in existence. At elevating of testing temperature, primarily, the adhesion bonds are broken at the boundaries of basalt (glass) – binder and in the matrix the cracks, parallel to the fiber, are formed, since U0 values for silicate fibers are equal to 350-385 kJ/mole and the values of activation energy of destruction of polymeric matrix comprise 125-190 kJ/mole. Intensity of breaking of adhesion bond: carbon-binder is of lesser importance, since U0 for polyacrylonitrile is near to U0 for binder (200 kJ/mole). In spite of this fact, in materials under study, breaking of adhesion bond doesn't lead to their destruction since reinforcing element continues an operation as the bundle of non-bound fibers. In this case minimal breaking stress for uni-directional basalt plastics is estimated as a half of breaking stress, obtained by standard testing of the material at normal temperature.

## **3. Mechanical properties of BP and HFRC**

## **3.1. Effect of duration of static loading and temperature on strength**

Dependence of breaking stress of BP and HFRC on temperature was estimated by the coefficients of operating conditions *K*T = σT / σs-t, where σT and σs-t are breaking stresses for the samples after temperature action and at short-term testing, respectively. The values of *K*<sup>T</sup> are presented in Table 5.

If in formula (1) it is granted that

$$T = T\_i = \text{const} \,, \text{ then } \sigma = \frac{\mathcal{U}\_0}{\mathcal{Y}} - A \lg \frac{\tau}{\tau\_0} \tag{4}$$

Properties of Basalt Plastics and of Composites Reinforced by Hybrid Fibers in Operating Conditions 253

**Figure 3.** Curves of long-term strength of BP-3, BP-4 (tension): 1-BP-3; 2-BP-4, uni-directional; 3 – BP-

lg τ, min

To estimate a time dependence of the strength, the coefficients of operating conditions of the material were used: *K*<sup>τ</sup> = στ / σs-t, where σ*τ* breaking stress after the time interval, corresponding to service life of the structure or item. The values *K*τ for BP and HFRC are given in Table 6.

**Figure 4.** Curves of long-term strength of BP-1 at various temperatures (bending). 1 – 313K; 2 – 333K

lg τ, min

4, full strength.

where lg *i i kT <sup>A</sup> <sup>e</sup>* .


Remark: 1. Coefficients of operating conditions of materials in the structures at temperature 273 K are taken to be unity; 2. At intermediate temperatures *K*T may be determined by interpolation.

**Table 5.** Coefficients of operating condition KT in the structures, operating at elevated temperatures

In regard to material under study, the linear relationship between strength and durability logarithm is mainly obeyed at normal as well as at the temperatures of 313K and 333K. Mentioned temperatures are considerably less than temperature of forced elasticity of BP and HFRC and because of this fact the dependence σ – lg τ on tension hasn't a kink, characteristic of the case of the action of high (>350K) temperatures. Below these dependences are presented in the coordinates σ – lg τ in contrast to the coordinates lg τ - σ, used in the theory of the strength of the solids (Fig. 3, 4).

are presented in Table 5.

where

If in formula (1) it is granted that

lg *i*

*i kT <sup>A</sup> <sup>e</sup>* .

polyacrylonitrile is near to U0 for binder (200 kJ/mole). In spite of this fact, in materials under study, breaking of adhesion bond doesn't lead to their destruction since reinforcing element continues an operation as the bundle of non-bound fibers. In this case minimal breaking stress for uni-directional basalt plastics is estimated as a half of breaking stress,

Dependence of breaking stress of BP and HFRC on temperature was estimated by the coefficients of operating conditions *K*T = σT / σs-t, where σT and σs-t are breaking stresses for the samples after temperature action and at short-term testing, respectively. The values of *K*<sup>T</sup>

0

(4)

Compression Bending Shearing

lg *<sup>U</sup> <sup>A</sup>*

obtained by standard testing of the material at normal temperature.

Material Temperature, K

unity; 2. At intermediate temperatures *K*T may be determined by interpolation.

used in the theory of the strength of the solids (Fig. 3, 4).

Tension,

**3.1. Effect of duration of static loading and temperature on strength** 

*<sup>i</sup> T T const* , then <sup>0</sup>

313 333

Compression Bending Shearing Tension,

BP-1 0.65 0.85 0.67 0.60 0.79 0.63 BP-2, BP-3 0.88 0.79 0.78 0.77 0.72 0.72 BP-4 0.70 0.88 0.72 0.63 0.78 0.66 HFRC-1 0.72 0.88 0.77 0.70 0.85 0.72 HFRC-2 0.72 0.82 0.82 0.70 0.79 0.77 HFRC-3 0.74 0.86 0.88 0.71 0.81 0.80 HFRC-4 0.75 0.85 0.79 0.74 0.78 0.75 Remark: 1. Coefficients of operating conditions of materials in the structures at temperature 273 K are taken to be

**Table 5.** Coefficients of operating condition KT in the structures, operating at elevated temperatures

In regard to material under study, the linear relationship between strength and durability logarithm is mainly obeyed at normal as well as at the temperatures of 313K and 333K. Mentioned temperatures are considerably less than temperature of forced elasticity of BP and HFRC and because of this fact the dependence σ – lg τ on tension hasn't a kink, characteristic of the case of the action of high (>350K) temperatures. Below these dependences are presented in the coordinates σ – lg τ in contrast to the coordinates lg τ - σ,

**3. Mechanical properties of BP and HFRC** 

**Figure 3.** Curves of long-term strength of BP-3, BP-4 (tension): 1-BP-3; 2-BP-4, uni-directional; 3 – BP-4, full strength.

To estimate a time dependence of the strength, the coefficients of operating conditions of the material were used: *K*<sup>τ</sup> = στ / σs-t, where σ*τ* breaking stress after the time interval, corresponding to service life of the structure or item. The values *K*τ for BP and HFRC are given in Table 6.

**Figure 4.** Curves of long-term strength of BP-1 at various temperatures (bending). 1 – 313K; 2 – 333K


Properties of Basalt Plastics and of Composites Reinforced by Hybrid Fibers in Operating Conditions 255

The analysis of the data of Table 7 confirms the fact that the method of coefficients multiplying really leads to enhanced values of the coefficients of operating conditions and consequently to overstating of calculated resistances of BP. Thus, it was decided to determine the coefficients of operating conditions for the joint action of external factors and

Deformability of the materials under study, caused by force action, was estimated by shortterm and long-term elasticity and shear modulus (*E*s-t, *E* <sup>ℓ</sup>-t, *G*s-t, *G*ℓ-t) were determined by short-term static testing of small standard samples as a ratio between the increment of stress and the increment of relative deformation of a sample. *E* <sup>ℓ</sup>-t, *G* <sup>ℓ</sup>-t were obtained by long-term static testing of the samples at stresses equal to calculated long-term resistance of materials as a ratio between the stress and maximum relative deformation of the sample at damping of creeping. It should be noted that the term "long-term elasticity modulus" is conventional in this case, since deformations of polymeric composites at long-term loading, in reality,

At the temperatures, no greater than the temperature of beginning of binder destruction, reinforcing fibers act as linear-elastic materials. Binders are characterized by visco-elastic properties. Therefore, deformations of BP and HFRC, generally, depend significantly on

As might be expected, in uni–directional or orthogonally-reinforced BP and HFRC, the creeping is formed at the action of constant loading applied to the direction of reinforcement. But after a time, this process is practically terminated. This fact is quite clear since at first an effort is distributed between fibers and binder, but stresses in binder relax

At loading of BP and HFRC, randomly reinforced and oriented at angle to loading direction, creeping isn't damped and is continued up to material destruction. Creeping anisotropy of these materials is expressed to a considerable more extent than an anisotropy of elastic

The goal of experiments for determination of creeping of BP and HFRC was an establishment of functional relationship between stress, deformation and duration of loading action. Some

As is seen, experimental points of all curves, plotted for various levels of stresses in the coordinates ε – τ, fall on one curve, constructed in the coordinates ε / ε o – τ, which allows to consider the material under study as linearly visco-elastic. Isochrones, constructed for this reason, are straight lines, reflecting a linear relationship between deformations and stresses

**3.2. Effect of the time of loading action and temperature on deformation** 

loading.

**characteristics** 

aren't elastic.

duration and temperature of operation.

for each fixed instant of time τi.

and all stresses are progressively imparted to fibers.

properties and sharply enhances with temperature elevation.

results of the study of BP and HFRC creeping are given in Fig. 5.

**Table 6.** The values of the coefficient *K*τ at various types of stressed state

Direct experimental determination of στ is fraught with great difficulties: the maintenance of constant external conditions and predetermined stress over a long period of time is necessary. Therefore the values στ were determined for three values: 1, 102, 103 hours by extrapolating on the basis of equation (1), obtained curve and by assuming that external factors don't distort a linear character of temporal dependence of the strength.

Hence, we have, separately, the coefficients of operating conditions providing the temperature influence as well as considering the loading duration. Over many years the method of multiplying of these coefficients has been used to account the joint effect of these factors on long-term resistance. But as it was shown in [11], this method leads to considerable overstating of calculated resistances of glass plastics, especially at the temperatures close to glass transition temperature of a binder. To check this fact, a materials under study were subjected to the joint action of loading and temperature (313 K, 333 K), correlating the data, obtained in this case with the values of the coefficients of operating conditions *K*τ and *K*T (Table 7).


**Table 7.** Values of coefficients of operating conditions of BP at bending

The analysis of the data of Table 7 confirms the fact that the method of coefficients multiplying really leads to enhanced values of the coefficients of operating conditions and consequently to overstating of calculated resistances of BP. Thus, it was decided to determine the coefficients of operating conditions for the joint action of external factors and loading.

## **3.2. Effect of the time of loading action and temperature on deformation characteristics**

254 Composites and Their Applications

0.71 0.86 - 0.81

0.91 0.88 0.90 0.81

conditions *K*τ and *K*T (Table 7).

Coefficient Temperature,

313 333

313 333

313 333

313 333

*K*<sup>T</sup>

*K*τ

*K*T *·K*<sup>τ</sup>

*T K*

(τ = 5 years)

*TK K K*

*T*

0.65 0.75 0.68 0.77

0.79 0.73 0.76 0.72 0.60 0.68 0.56 0.70

0.69 0.66 0.71 0.62

**Table 6.** The values of the coefficient *K*τ at various types of stressed state

BP-1 BP-2 BP-3 BP-4

HFRC - 1 HFRC - 2 HFRC - 3 HFRC - 4

Material Tension Compression Bending

0.71 0.81 0.88 0.89

0.85 0.82 0.88 0.79

Direct experimental determination of στ is fraught with great difficulties: the maintenance of constant external conditions and predetermined stress over a long period of time is necessary. Therefore the values στ were determined for three values: 1, 102, 103 hours by extrapolating on the basis of equation (1), obtained curve and by assuming that external

Hence, we have, separately, the coefficients of operating conditions providing the temperature influence as well as considering the loading duration. Over many years the method of multiplying of these coefficients has been used to account the joint effect of these factors on long-term resistance. But as it was shown in [11], this method leads to considerable overstating of calculated resistances of glass plastics, especially at the temperatures close to glass transition temperature of a binder. To check this fact, a materials under study were subjected to the joint action of loading and temperature (313 K, 333 K), correlating the data, obtained in this case with the values of the coefficients of operating

<sup>K</sup>BP - 1 BP - 2 BP - 3 BP - 4

0.90 0.85

0.80 0.76

0.75 0.69

0.94 0.91 0.85 0.79

0.71 0.66

0.65 0.59

0.91 0.89

0.88 0.72

0.72 0.59

0.69 0.49

0.95 0.83

factors don't distort a linear character of temporal dependence of the strength.

0.84 0.65

0.44 0.34

0.41 0.28

0.93 0.82

**Table 7.** Values of coefficients of operating conditions of BP at bending

(τ = 5 years) 0.52 0.82 0.89 0.83

103h 104h 105h 103h 104h 105h 103h 10 4h 105h

0.68 0.67 0.77 0.78

0.76 0.71 0.77 0.70 0.58 0.59 0.61 0.51

0.62 0.59 0.68 0.62 0.68 0.83 0.87 0.78

0.78 0.80 0.82 0.80 0.56 0.72 0.74 0.72

0.69 0.63 0.66 0.63 0.45 0.55 0.59 0.63

0.55 0.51 0.59 0.49

Deformability of the materials under study, caused by force action, was estimated by shortterm and long-term elasticity and shear modulus (*E*s-t, *E* <sup>ℓ</sup>-t, *G*s-t, *G*ℓ-t) were determined by short-term static testing of small standard samples as a ratio between the increment of stress and the increment of relative deformation of a sample. *E* <sup>ℓ</sup>-t, *G* <sup>ℓ</sup>-t were obtained by long-term static testing of the samples at stresses equal to calculated long-term resistance of materials as a ratio between the stress and maximum relative deformation of the sample at damping of creeping. It should be noted that the term "long-term elasticity modulus" is conventional in this case, since deformations of polymeric composites at long-term loading, in reality, aren't elastic.

At the temperatures, no greater than the temperature of beginning of binder destruction, reinforcing fibers act as linear-elastic materials. Binders are characterized by visco-elastic properties. Therefore, deformations of BP and HFRC, generally, depend significantly on duration and temperature of operation.

As might be expected, in uni–directional or orthogonally-reinforced BP and HFRC, the creeping is formed at the action of constant loading applied to the direction of reinforcement. But after a time, this process is practically terminated. This fact is quite clear since at first an effort is distributed between fibers and binder, but stresses in binder relax and all stresses are progressively imparted to fibers.

At loading of BP and HFRC, randomly reinforced and oriented at angle to loading direction, creeping isn't damped and is continued up to material destruction. Creeping anisotropy of these materials is expressed to a considerable more extent than an anisotropy of elastic properties and sharply enhances with temperature elevation.

The goal of experiments for determination of creeping of BP and HFRC was an establishment of functional relationship between stress, deformation and duration of loading action. Some results of the study of BP and HFRC creeping are given in Fig. 5.

As is seen, experimental points of all curves, plotted for various levels of stresses in the coordinates ε – τ, fall on one curve, constructed in the coordinates ε / ε o – τ, which allows to consider the material under study as linearly visco-elastic. Isochrones, constructed for this reason, are straight lines, reflecting a linear relationship between deformations and stresses for each fixed instant of time τi.

Properties of Basalt Plastics and of Composites Reinforced by Hybrid Fibers in Operating Conditions 257

were constructed, by which the dependence of elasticity modulus

Creeping of HFRC has been investigated. The levels of relative stress, that is to say, ratio between acting stress and breaking one comprised 0.4; 0.5; 0.6; 0.7; 0.8; Experimental curves of creeping of the composite HFRC are presented in Fig. 6. By creeping curves the families

on time was found. After 104 hours the reduction of elasticity modulus comprised 10-12%.

**Figure 7.** Curves of BP-1 creeping at tension 1-70MPa; 2-65 MPa; 3-40 MPa; 4-20 MPa; 5-10MPa.

**Figure 8.** Curves of BP-1 creeping at bending for stress levels: 1-50MPa; 2-20 MPa.

action and on temperature variation.

indicative of the presence of power dependence of deformation creeping on time.

Creeping plots at the coordinates lgε - lgτ present a series of parallel straight lines, which is

In Table 8, 9 the values of the coefficients of operating conditions are given, considering the variation of deformation characteristics of BP and HFRC depending on duration of loading

Creeping of BP-1 exhibits non-damped character. Deformation of creeping at tension over 5·103-1·104 hours appears to be several times more than instantly-elastic ones (Fig.7). Similar

of isochronic curves

 

picture is observed for other types of stressed state (Fig.8).

**Figure 5.** Curves of creeping (a) and generalized curve of creeping (b) for basalt cloth-base laminate at compression on cloth weft. Stresses: 1-90 MPa, 2 – 85MPa; 3 – 65MPa; 4 – 50 MPa.

**Figure 6.** Creeping of the composite HFRC–4. 1,2,3,4,5, respectively, are the levels of relative stress: 0.4; 0.5; 0.6; 0.7; 0.8.

Creeping of HFRC has been investigated. The levels of relative stress, that is to say, ratio between acting stress and breaking one comprised 0.4; 0.5; 0.6; 0.7; 0.8; Experimental curves of creeping of the composite HFRC are presented in Fig. 6. By creeping curves the families of isochronic curves were constructed, by which the dependence of elasticity modulus on time was found. After 104 hours the reduction of elasticity modulus comprised 10-12%.

256 Composites and Their Applications

0.5; 0.6; 0.7; 0.8.

**Figure 5.** Curves of creeping (a) and generalized curve of creeping (b) for basalt cloth-base laminate at

**Figure 6.** Creeping of the composite HFRC–4. 1,2,3,4,5, respectively, are the levels of relative stress: 0.4;

lg τ, h

compression on cloth weft. Stresses: 1-90 MPa, 2 – 85MPa; 3 – 65MPa; 4 – 50 MPa.

ε, %

Creeping of BP-1 exhibits non-damped character. Deformation of creeping at tension over 5·103-1·104 hours appears to be several times more than instantly-elastic ones (Fig.7). Similar picture is observed for other types of stressed state (Fig.8).

**Figure 7.** Curves of BP-1 creeping at tension 1-70MPa; 2-65 MPa; 3-40 MPa; 4-20 MPa; 5-10MPa.

**Figure 8.** Curves of BP-1 creeping at bending for stress levels: 1-50MPa; 2-20 MPa.

Creeping plots at the coordinates lgε - lgτ present a series of parallel straight lines, which is indicative of the presence of power dependence of deformation creeping on time.

In Table 8, 9 the values of the coefficients of operating conditions are given, considering the variation of deformation characteristics of BP and HFRC depending on duration of loading action and on temperature variation.


Properties of Basalt Plastics and of Composites Reinforced by Hybrid Fibers in Operating Conditions 259

bench testing on natural ageing of BP and HFRC in environmental conditions of South

Ageing of BP and HFRC, intended for operation in atmospheric conditions, is a result of complex action of such factors as chain reaction of oxidation, temperature-humid deformation of a binder, penetration of moisture into material with further leaching of fiber,

Exposure of BP and HERC in unloaded state and under stresses, close to calculated resistances of materials, revealed a considerable difference in the character of development of ageing processes in loaded and unloaded composites, as well as a difference between the values of long-term resistance and creeping of the samples, tested in atmospheric and laboratory conditions. For example, in Fig 9 the behavior of the samples of BP-2, unloaded

**Figure 9.** Dependence of strength at BP-2 tension on ageing time at open air and on the level of action

Binder nature has a pronounced effect on atmospheric resistance of BP and HFRC. It is difficult to judge about atmospheric ageing of BP and HFRC on the basis of polyester matrix, since the process of binder hardening isn't finished; this leads to enhancement of elasticity modulus by 5-15%. True enough, the strength reduction by 8-17% still takes place. As a result of atmospheric ageing, mechanical characteristics of BP and HFRC on the basis of epoxy and phenol-formaldehyde matrixes are gradually decreased depending on material thickness and applied stress. Difference in the variation of mechanical indexes of loaded and unloaded samples is revealed to a greater extent than in BP and HFRC on the basis of polyester matrix. Ageing process of materials are developed, mainly, on the surface; in this connection their atmospheric resistance significantly depends on material thickness. Existence of stressed state has a pronounced effect on intensification of ageing of BP and

Caucasus.

abrasive action of dust.

and loaded by various intensity are shown.

stress: 1 - zero stress, 2 – 0.2 σs-t, 3 – 0.45 σs-t, 4 – 0.70 σs-t



**Table 9.** The values of the coefficients of operating conditions *K*T by deformation properties

## **4. Resistance of BP and HFRC to environment**

#### **4.1. Mechanical characteristics at atmospheric action**

It is well known that by selecting of corresponding regimes of accelerated testing on atmospheric resistance the reduction of mechanical characteristics of materials may be relatively readily attained. But the determination of reasonably accurate correlation between the results of natural and accelerated testing on ageing of polymeric composites was unsuccessful. So far as we know, this problem wasn't solved up till now in relation to inorganic as well as to organic materials. In this connection it was decided to perform the bench testing on natural ageing of BP and HFRC in environmental conditions of South Caucasus.

258 Composites and Their Applications

Material Index

BP-1 Et

BP-2 Et

BP-3 Et

BP-4 Et

HFRC - 1 Et

HFRC - 2 Et

HFRC - 3 Et

HFRC - 4 Et

Material Index

G

G

G

G

BP-1 Et

BP-2 Et

BP-3 Et

BP-4 Et

G

*G* 

*G* 

G

G

G

G

G

0.53 0.51

0.71 0.81

0.88 0.83

0.78 0.77

**4. Resistance of BP and HFRC to environment** 

**4.1. Mechanical characteristics at atmospheric action** 

0.72 0.69

0.91 0.89

0.95 0.72

0.91 0.85

0.92 0.85

0.88 0.79

0.95 0.91

0.89 0.81

*<sup>K</sup>*T at temperatures Material Index

0.39 HFRC-1 Et

0.74 HFRC-2 Et

0.74 HFRC-3 Et

0.85 HFRC-4 Et

**Table 8.** The values of the coefficients of operating conditions *K*τ by deformation properties

0.42

0.64

0.76

0.61

It is well known that by selecting of corresponding regimes of accelerated testing on atmospheric resistance the reduction of mechanical characteristics of materials may be relatively readily attained. But the determination of reasonably accurate correlation between the results of natural and accelerated testing on ageing of polymeric composites was unsuccessful. So far as we know, this problem wasn't solved up till now in relation to inorganic as well as to organic materials. In this connection it was decided to perform the

**Table 9.** The values of the coefficients of operating conditions *K*T by deformation properties

*K*τ**,** after hours 103 104 105

> 0.61 0.59

> 0.82 0.85

> 0.89 0.68

> 0.86 0.79

> 0.87 0.76

> 0.82 0.71

> 0.89 0.86

> 0.82 0.72

> > G

G

G

G

313K 333K 313K 333K

0.52 0.50

0.78 0.79

0.82 0.62

0.82 0.71

0.85 0.69

0.79 0.62

0.85 0.78

0.75 0.69

*K*T at temperatures

0.79 0.75

0.72 0.71

0.82 0.79

0.85 0.72

0.85 0.82

0.82 0.79

0.89 0.85

0.82 0.80 Ageing of BP and HFRC, intended for operation in atmospheric conditions, is a result of complex action of such factors as chain reaction of oxidation, temperature-humid deformation of a binder, penetration of moisture into material with further leaching of fiber, abrasive action of dust.

Exposure of BP and HERC in unloaded state and under stresses, close to calculated resistances of materials, revealed a considerable difference in the character of development of ageing processes in loaded and unloaded composites, as well as a difference between the values of long-term resistance and creeping of the samples, tested in atmospheric and laboratory conditions. For example, in Fig 9 the behavior of the samples of BP-2, unloaded and loaded by various intensity are shown.

**Figure 9.** Dependence of strength at BP-2 tension on ageing time at open air and on the level of action stress: 1 - zero stress, 2 – 0.2 σs-t, 3 – 0.45 σs-t, 4 – 0.70 σs-t

Binder nature has a pronounced effect on atmospheric resistance of BP and HFRC. It is difficult to judge about atmospheric ageing of BP and HFRC on the basis of polyester matrix, since the process of binder hardening isn't finished; this leads to enhancement of elasticity modulus by 5-15%. True enough, the strength reduction by 8-17% still takes place.

As a result of atmospheric ageing, mechanical characteristics of BP and HFRC on the basis of epoxy and phenol-formaldehyde matrixes are gradually decreased depending on material thickness and applied stress. Difference in the variation of mechanical indexes of loaded and unloaded samples is revealed to a greater extent than in BP and HFRC on the basis of polyester matrix. Ageing process of materials are developed, mainly, on the surface; in this connection their atmospheric resistance significantly depends on material thickness. Existence of stressed state has a pronounced effect on intensification of ageing of BP and HFRC on the basis of epoxy and phenol-formaldehyde binders in atmospheric conditions; in this case the effect of materials thickness is reflected to the greatest extent. Thus, a great number of BP-2 samples of 1.0 mm thickness, exposed at stress of 0.75 σs-t, were destructed immediately at the stand before expected exposure time, whereas the samples of 4.5 mm thickness weren't destroyed. The results of mechanical testing have shown a slight reduction of the strength of these samples (stresses in both cases were equal).

Properties of Basalt Plastics and of Composites Reinforced by Hybrid Fibers in Operating Conditions 261

of strength of fibers and of materials on their base at normal temperature is observed within first 200-240 hours, after which some stabilization of their strength indexes takes place. After maintenance in corrosive media the samples of threads were tested on the machine at relative humidity of air – 75-78% by determination of breaking load – P (P0 – breaking load of dry threads). Because of some reversibility of strength reduction in fibers at the action of

As is seen from the data of Table 11, 5-10% solutions of caustic soda have the most destructive effect on alkalineless threads. With increasing of the concentration of NaOH, the

With increasing of the temperature of alkaline solution the total solubility of glass fiber enhances. In this case maximum solubility is slightly smoothed, in doing so its displacement is observed to the realm of higher concentrations. For basalt threads, in principle, the same character of the strength dependence on temperature and solution concentration is

The most intensive strength reduction for glass threads is also observed at the action of 5-

Residual strength

*o p p*

1% 5% 10% 25% 45%\*\*

33 45

5 21

5 24

> 0.03 0.01

100%

56 67

16 31

17 38

> 0.03 0.01

59 72

18 42

19 42

2.33 1.49

corrosive media, the samples of threads didn't dried before testing on the machine.

stability of strength characteristics of threads enhanced.

Corrosive media\*

Caustic soda <sup>35</sup>

Sulphuric acid <sup>22</sup>

Nitric acid <sup>6</sup>

Mass loss, mg.cm-2, hour-1

alkalineless glass and from basalt.

45

27

21

\*\* maximum concentration of H2SO4 – 45%, of HNO3-60%.

\* reduction of glass threads in water comprised 40%, of basalt threads 15%.

0.03 0.01

observed, but the values of mass loss is significantly lower (Table 12).

10% NaOH. Residual strength of basalt threads is considerably higher (Fig10).

32 41

4 18

4 19

Remark: in numerator – indexes of threads from alkalineless glass; In denominator - indexes of basalt threads.

**Table 11.** Reduction of breaking strength of threads in corrosive media of various concentration

0.06 0.03

**Table 12.** Effect of temperature and caustic soda concentration on mass variation of fibers from

Temperature, K 313 323 333 343 363

Remark: in numerator – the values of glass threads of alkalineless composition; In denominator-the values for basalt threads.

As a result of performed investigations, the values of the coefficients of operating conditions of BP and HFRC in service, have been obtained (Table 10).


**Table 10.** Coefficients of operating conditions – *K*atm of BP and HFRC

## **4.2. Mechanical characteristics at the action of water and some corrosive liquid media**

Stability of mechanical properties of BP and HFRC is determined by resistance of reinforcing component of material, matrix and adhesion bond between them to aqueous and chemical media. An advantage of basalt fiber over other ones, in addition to higher thermal stability, must consist in water resistance and chemical endurance. In order to prove this fact, the action of alkali and mineral acids of various concentration (up to 60%) was studied on threads strength from alkalineless, alkaline and basalt glass, used in composites. Chemical composition of these glasses is the following (in mass%): aluminumborosilicate (alkalineless ) – SiO2-54; Al2O3 – 14; B2O3 – 10; CaO-16; MgO-4; Na2O – 2; sodiumcalciumsilicate (alkaline) - SiO2-71; Al2O3 – 3; CaO-8; MgO-3; Na2O – 15; basalt one: SiO2-49; Al2O3 – 16; Fe2O3 – 10; CaO – 9; MgO-7; Na2O-4; MnO<1; TiO2<1. It was studied the behavior of roving, offering the non-twisted strand with a diameter of elementary fiber of the order of 10-16μ.

Testing was carried out in water and in the media, most characteristic for chemical production: in caustic soda, sulphuric and nitric acids. Solution temperature comprised 291- 295K. Before testing the samples were preliminary conditioned. Duration of static action of corrosive medium on threads was taken to be 240 hours, since the most intensive reduction of strength of fibers and of materials on their base at normal temperature is observed within first 200-240 hours, after which some stabilization of their strength indexes takes place. After maintenance in corrosive media the samples of threads were tested on the machine at relative humidity of air – 75-78% by determination of breaking load – P (P0 – breaking load of dry threads). Because of some reversibility of strength reduction in fibers at the action of corrosive media, the samples of threads didn't dried before testing on the machine.

As is seen from the data of Table 11, 5-10% solutions of caustic soda have the most destructive effect on alkalineless threads. With increasing of the concentration of NaOH, the stability of strength characteristics of threads enhanced.

With increasing of the temperature of alkaline solution the total solubility of glass fiber enhances. In this case maximum solubility is slightly smoothed, in doing so its displacement is observed to the realm of higher concentrations. For basalt threads, in principle, the same character of the strength dependence on temperature and solution concentration is observed, but the values of mass loss is significantly lower (Table 12).

The most intensive strength reduction for glass threads is also observed at the action of 5- 10% NaOH. Residual strength of basalt threads is considerably higher (Fig10).


Remark: in numerator – indexes of threads from alkalineless glass; In denominator - indexes of basalt threads. \* reduction of glass threads in water comprised 40%, of basalt threads 15%.

\*\* maximum concentration of H2SO4 – 45%, of HNO3-60%.

260 Composites and Their Applications

**media** 

HFRC on the basis of epoxy and phenol-formaldehyde binders in atmospheric conditions; in this case the effect of materials thickness is reflected to the greatest extent. Thus, a great number of BP-2 samples of 1.0 mm thickness, exposed at stress of 0.75 σs-t, were destructed immediately at the stand before expected exposure time, whereas the samples of 4.5 mm thickness weren't destroyed. The results of mechanical testing have shown a slight

As a result of performed investigations, the values of the coefficients of operating conditions

**4.2. Mechanical characteristics at the action of water and some corrosive liquid** 

Stability of mechanical properties of BP and HFRC is determined by resistance of reinforcing component of material, matrix and adhesion bond between them to aqueous and chemical media. An advantage of basalt fiber over other ones, in addition to higher thermal stability, must consist in water resistance and chemical endurance. In order to prove this fact, the action of alkali and mineral acids of various concentration (up to 60%) was studied on threads strength from alkalineless, alkaline and basalt glass, used in composites. Chemical composition of these glasses is the following (in mass%): aluminumborosilicate (alkalineless ) – SiO2-54; Al2O3 – 14; B2O3 – 10; CaO-16; MgO-4; Na2O – 2; sodiumcalciumsilicate (alkaline) - SiO2-71; Al2O3 – 3; CaO-8; MgO-3; Na2O – 15; basalt one: SiO2-49; Al2O3 – 16; Fe2O3 – 10; CaO – 9; MgO-7; Na2O-4; MnO<1; TiO2<1. It was studied the behavior of roving, offering the

Testing was carried out in water and in the media, most characteristic for chemical production: in caustic soda, sulphuric and nitric acids. Solution temperature comprised 291- 295K. Before testing the samples were preliminary conditioned. Duration of static action of corrosive medium on threads was taken to be 240 hours, since the most intensive reduction

non-twisted strand with a diameter of elementary fiber of the order of 10-16μ.

BP-1 0.69 0.80 Presented coefficients

For long-term elasticity modulus Remark

are given for BP-1 of 1.5-3.0 mm thickness, for BP-2, BP-3 and BP-4 of 2.0-7.0 mm thickness and for all types of HFRC – 5.0- 8.0 mm of thickness.

reduction of the strength of these samples (stresses in both cases were equal).

resistances

BP-2 0.75 0.82 BP-3 0.79 0.83 BP-4 0.72 0.75 HFRC-1 0.82 0.85 HFRC-2 0.79 0.81 HFRC-3 0.85 0.88 HFRC-4 0.79 0.82

**Table 10.** Coefficients of operating conditions – *K*atm of BP and HFRC

of BP and HFRC in service, have been obtained (Table 10).

Material For calculated

**Table 11.** Reduction of breaking strength of threads in corrosive media of various concentration


Remark: in numerator – the values of glass threads of alkalineless composition; In denominator-the values for basalt threads.

**Table 12.** Effect of temperature and caustic soda concentration on mass variation of fibers from alkalineless glass and from basalt.

Properties of Basalt Plastics and of Composites Reinforced by Hybrid Fibers in Operating Conditions 263

, the comparison of which with *K*T·*K*τ·*K*W once again

*w*

*K K K* 

*w*

are coefficients of operating conditions in aqueous medium,

Similar character in discordance of the values of the coefficients of operating conditions was also found at accounting of one more factor – temperature. Diagrams of long-term resistance of BP-1 at air and in water at the temperatures of 293K, 313K and 333K, presented in Fig. 12,

As indicated earlier, the joint effect of environment and time of its action on long-term resistance of materials to destruction is every so often estimated by multiplying of corresponding coefficients of operating conditions. But as with separate accounting of the effect of duration of the action stresses and temperature, this method causes the considerable errors in direction of reduction of safety factor. This fact is evident by the data

BP-1 0.89 0.52 0.46 0.40 0.87 BP-2 0.79 0.82 0.65 0.59 0.91 BP-3 0.82 0.89 0.72 0.60 0.83 BP-4 0.85 0.83 0.71 0.66 0.93 HFRC-1 0.90 0.88 0.79 0.70 0.89 HFRC-2 0.83 0.83 0.69 0.62 0.90 HFRC-3 0.89 0.82 0.73 0.68 0.93 HFRC-4 0.83 0.79 0.66 0.61 0.92 **Table 13.** Comparison of the coefficients of operating conditions obtained by accounting of separate

**Figure 12.** Long-term resistance of HFRC-2 at air and in water at the temperatures 293K(1,4), 313K (2,5)

*WKT* 

and at the joint effect of water and duration of its action, respectively.

Material Kw K<sup>τ</sup> Kτ · Kw *<sup>w</sup> K*

and joint action of water and of duration of its action on materials (at τ = 104 hours).

convinces in incorrectness of the method of coefficients multiplying (Table 14).

as an example, permit to determine ,

of Table 13, where Kw and *<sup>w</sup> K*

and 333K (3,6). 1, 2, 3 - at air; 4, 5, 6 - in water

**Figure 10.** Strength reduction of threads from alkaline glass (1) and from basalt (2) in caustic soda.

**Figure 11.** Variation of strength of alkaline glass threads ( ) and basalt ones (---) in sulphuric (1) and nitric (2) acids.

Testing of glass and basalt threads in sulphuric and nitric acids has shown that a factor of concentration exerts a lesser influence on the variation of strength characteristics. By the example of behavior of alkaline glass threads it may be noted a some increased influence of sulphuric and nitric acids on them in concentration range of 5-10%. But effect of this influence is very limited. Especially it may be said in relation to basalt threads (Fig 11).

Action of acids in the range of higher (>20%) concentrations is different. Concentration factor of nitric acid doesn't effect on strength of glass threads as well as of basalt ones. At the action of sulphuric acid (40%) a sharp decrease of the strength of glass threads is observed and an effect on the strength of basalt threads is not so noticeable (Fig 11).

Data on strength reduction in threads from alkalineless glass and basalt threads in sulphuric and nitric acids are presented in Table 11. Sulphuric acid acts considerably more aggressively in concentration range of 5-10%. Concentration factor of nitric acid doesn't effect significantly on the value of strength reduction of glass threads. The character of acid action on basalt threads remains identical but a level of residual strength of these threads after exposure in the media remains higher in comparison with a level of the strength of alkalineless glass threads.

Similar character in discordance of the values of the coefficients of operating conditions was also found at accounting of one more factor – temperature. Diagrams of long-term resistance of BP-1 at air and in water at the temperatures of 293K, 313K and 333K, presented in Fig. 12, as an example, permit to determine , *WKT* , the comparison of which with *K*T·*K*τ·*K*W once again convinces in incorrectness of the method of coefficients multiplying (Table 14).

262 Composites and Their Applications

nitric (2) acids.

alkalineless glass threads.

**Figure 10.** Strength reduction of threads from alkaline glass (1) and from basalt (2) in caustic soda.

**Figure 11.** Variation of strength of alkaline glass threads ( ) and basalt ones (---) in sulphuric (1) and

Testing of glass and basalt threads in sulphuric and nitric acids has shown that a factor of concentration exerts a lesser influence on the variation of strength characteristics. By the example of behavior of alkaline glass threads it may be noted a some increased influence of sulphuric and nitric acids on them in concentration range of 5-10%. But effect of this influence is very limited. Especially it may be said in relation to basalt threads (Fig 11).

Action of acids in the range of higher (>20%) concentrations is different. Concentration factor of nitric acid doesn't effect on strength of glass threads as well as of basalt ones. At the action of sulphuric acid (40%) a sharp decrease of the strength of glass threads is observed

Data on strength reduction in threads from alkalineless glass and basalt threads in sulphuric and nitric acids are presented in Table 11. Sulphuric acid acts considerably more aggressively in concentration range of 5-10%. Concentration factor of nitric acid doesn't effect significantly on the value of strength reduction of glass threads. The character of acid action on basalt threads remains identical but a level of residual strength of these threads after exposure in the media remains higher in comparison with a level of the strength of

and an effect on the strength of basalt threads is not so noticeable (Fig 11).

As indicated earlier, the joint effect of environment and time of its action on long-term resistance of materials to destruction is every so often estimated by multiplying of corresponding coefficients of operating conditions. But as with separate accounting of the effect of duration of the action stresses and temperature, this method causes the considerable errors in direction of reduction of safety factor. This fact is evident by the data of Table 13, where Kw and *<sup>w</sup> K* are coefficients of operating conditions in aqueous medium, and at the joint effect of water and duration of its action, respectively.


**Table 13.** Comparison of the coefficients of operating conditions obtained by accounting of separate and joint action of water and of duration of its action on materials (at τ = 104 hours).

**Figure 12.** Long-term resistance of HFRC-2 at air and in water at the temperatures 293K(1,4), 313K (2,5) and 333K (3,6). 1, 2, 3 - at air; 4, 5, 6 - in water


Properties of Basalt Plastics and of Composites Reinforced by Hybrid Fibers in Operating Conditions 265

caustic soda after 240-hour maintenance shows that general character of strength variation is identical in all cases (Fig. 13). The greatest reduction of strength is observed in 5-10% solutions of caustic soda. In concentrated solutions the strength, practically, remains at initial level. Such character of strength variation is retained for all structural directions of BP and HFRC. In Fig.14 strength variation for main structural directions is presented at bending of HFRC-4 after 240 hour maintenance in the solution of caustic soda. It is evident that maximum reduction of strength limit, in all cases, takes place in the range of concentration of caustic soda of 5-10%.

**Figure 14.** Strength reduction at various structural directions at bending of BP-2 in caustic soda. 1-on

The character of strength variation for BP and HFRC, depending on acid concentration, is determined, mainly, by inertia of a binder and by its adhesion to reinforcing fiber. Polyester BP, in comparison with phenol-formaldehyde ones, exhibit better resistance to the action of mineral acids, their strength properties are more stable. In 5-10% solutions of sulphuric acid the penetration of liquid into phenol-formaldehyde BP takes place; this fact reduces an adhesion of a binder to basalt fiber and causes the swelling of the samples of BP-4. Its

**Figure 13.** Strength reduction at tension of BP in caustic soda

warp; 2-on weft; 3-at an angle of 450

**Table 14.** Comparison of the coefficients of operating conditions, calculated by accounting of separate and joint effects of water, temperature and duration of their action on materials (at τ=104 hours)

Analysis of obtained data permits to conclude that if at room temperature the physical character of water action on BP and HFRC is dominated, then by temperature elevation the chemical activity of aqueous medium becomes predominant. It may be also concluded that a long-term operation of materials under study don't cause a sharp decrease of their loadcarrying capacity and destruction, since the medium temperature (313K, 333K) is significantly lower then the glass transition temperature of the binders and reinforcing elements (basalt, glass, carbon) are sufficiently stable in these conditions.

Going to the problem of chemical resistance of BP and HFRC, first and foremost it should be noted that the character of variation of their strength in alkaline media to a large extent depends on the composition of reinforcing component of materials, whereas an acid effect depends, mainly, on acid resistance of a matrix. Correlation of strength indexes of materials with epoxy, phenol-formaldehyde and polyester binders depending on the concentration of caustic soda after 240-hour maintenance shows that general character of strength variation is identical in all cases (Fig. 13). The greatest reduction of strength is observed in 5-10% solutions of caustic soda. In concentrated solutions the strength, practically, remains at initial level. Such character of strength variation is retained for all structural directions of BP and HFRC. In Fig.14 strength variation for main structural directions is presented at bending of HFRC-4 after 240 hour maintenance in the solution of caustic soda. It is evident that maximum reduction of strength limit, in all cases, takes place in the range of concentration of caustic soda of 5-10%.

**Figure 13.** Strength reduction at tension of BP in caustic soda

264 Composites and Their Applications

Material Tempera-

BP-1 293

BP-2 293

BP-3 293

BP-4 293

HFRC-1 293

HFRC-2 293

HFRC-3 293

HFRC-4 293

313 333

313 333

313 333

313 333

313 333

313 333

313 333

313 333 0.95 0.85 0.72

0.96 0.87 0.73

0.95 0.83 0.70

0.97 0.82 0.74

0.98 0.85 0.78

1.00 0.90 0.81

1.00 0.88 0.80

1.00 0.84 0.72

ture, K KT Kw K<sup>τ</sup> *<sup>K</sup>*T · *K*w · *K*<sup>τ</sup> *<sup>T</sup>*,

0.52

0.82

0.89

0.83

0.88

0.83

0.82

0.79

**Table 14.** Comparison of the coefficients of operating conditions, calculated by accounting of separate and joint effects of water, temperature and duration of their action on materials (at τ=104 hours)

Analysis of obtained data permits to conclude that if at room temperature the physical character of water action on BP and HFRC is dominated, then by temperature elevation the chemical activity of aqueous medium becomes predominant. It may be also concluded that a long-term operation of materials under study don't cause a sharp decrease of their loadcarrying capacity and destruction, since the medium temperature (313K, 333K) is significantly lower then the glass transition temperature of the binders and reinforcing

Going to the problem of chemical resistance of BP and HFRC, first and foremost it should be noted that the character of variation of their strength in alkaline media to a large extent depends on the composition of reinforcing component of materials, whereas an acid effect depends, mainly, on acid resistance of a matrix. Correlation of strength indexes of materials with epoxy, phenol-formaldehyde and polyester binders depending on the concentration of

0.89 0.86 0.86

0.79 0.78 0.76

0.82 0.82 0.69

0.85 0.85 0.80

0.90 0.85 0.81

0.83 0.81 0.79

0.89 0.87 0.82

0.84 0.83 0.80

elements (basalt, glass, carbon) are sufficiently stable in these conditions.

*wK* 

0.42 0.30 0.20

0.61 0.35 0.27

0.67 0.43 0.28

0.65 0.57 0.30

0.77 0.54 0.33

0.66 0.54 0.32

0.70 0.57 0.33

0.61 0.43 0.27

0.44 0.38 0.32

0.62 0.56 0.45

0.69 0.61 0.43

0.68 0.58 0.49

0.78 0.64 0.56

0.69 0.61 0.53

0.73 0.63 0.54

0.66 0.55 0.46  , *T*

*T wK*

*KK K w* 

> 0.95 0.79 0.62

> 0.98 0.62 0.60

> 0.97 0.70 0.65

> 0.96 0.98 0.61

> 0.99 0.84 0.59

> 0.96 0.89 0.60

> 0.96 0.90 0.61

> 0.92 0.78 0.59

**Figure 14.** Strength reduction at various structural directions at bending of BP-2 in caustic soda. 1-on warp; 2-on weft; 3-at an angle of 450

The character of strength variation for BP and HFRC, depending on acid concentration, is determined, mainly, by inertia of a binder and by its adhesion to reinforcing fiber. Polyester BP, in comparison with phenol-formaldehyde ones, exhibit better resistance to the action of mineral acids, their strength properties are more stable. In 5-10% solutions of sulphuric acid the penetration of liquid into phenol-formaldehyde BP takes place; this fact reduces an adhesion of a binder to basalt fiber and causes the swelling of the samples of BP-4. Its strength limit at tension is gradually reduced and in the range of medium concentrations is practically unchanged (Fig. 15).

Properties of Basalt Plastics and of Composites Reinforced by Hybrid Fibers in Operating Conditions 267

*<sup>t</sup> K* on a logarithm of durability at the bending of BP-1.

0.64 0.36 0.20 0.18 0.21

4

**Table 15.** Coefficients of long-term resistances of BP-1 in water and in the solutions of caustic soda and

Processing of these and other above-presented results of investigations, for all materials, considered in this work, permitted to obtain the reference data on long-term calculated resistances of BP and HFRC. These data, by our opinion, may be beneficial at designing of

At present a sufficient experience is accumulated in world practice in the field of the technology of preparation of basalt plastics and composite materials with reinforcing structures from hybrid fibers. Development of the works along this line is determined by possibility of preparation of new generation of materials with a wide spectrum of properties. Along with it, a diversity of the requirements, imposed to structural materials, tended to the fact that none of newly elaborated materials can occupy the dominant place at current stage of technology development, at least, in the immediate future. Each type of materials may be optimal in certain specific cases, as shown in presented work. A wide spectrum of needed materials, apart from considered here, may be prepared by the use of a number of reinforcing fibers with various elastic and strength characteristics and combined

Proposed time of exploitation Up to 1 year To 3 years To 5 years To 10years

> 0.62 0.33 0.18 0.15 0.19

0.58 0.29 0.15 0.11 0.16

1 – water; 2 – H2SO4; 3 – HNO3; 4 – NaOH **Figure 16.** Dependence of *w cor*

> 0.67 0.42 0.22 0.20 0.25

structures and items by the use of BP and HFRC.

Operating conditions

Dry state Water 1% NaOH 1% H2SO4 1 % HNO3

**5. Conclusion** 

acids

Nitric acid is a powerful oxidizer and even at low temperatures causes the breakage of the surface of phenol-formaldehyde BP, with leads to definite losses in its mass. By increasing of acid concentration the swelling of the samples of BP-2 takes place but its strength in the range of low concentrations is varied moderately. By increasing of acid concentration strength drop is continued (Fig.15).

**Figure 15.** Strength variation at tension of BP-2 in sulphuric (1) and nitric (2) acids

At long-term action of sulphuric acid on polyester BP the breaking of the surface of the samples of BP-1 takes place accompanying by the loss of its mass and strength reduction. True enough, this process occurs only at low concentrations (up to 5%) and in the solutions of higher concentrations the strength remains at original level. Concentrated nitric acid depending on the time of action on polyester BP, causes an intensive swelling or washing-out of the samples. Strength of BP-1 is gradually decreased by increasing of the concentration of nitric acid.

The further stage of the work was the determination of long-term resistance of BP and HFRC in water and in 1 % solutions of caustic soda, sulphuric and nitric acids. Long-term resistance of BP and HFRC on bending was studied by the procedure, described in [12]. Long-term resistance of the materials, operating in water and corrosive liquid media, is nothing more nor less than the coefficient of their operating conditions, accounting the joint action of temporal factor and of water or anyone corrosive medium on the materials. For example, in fig.16, the dependence of *w cor <sup>K</sup><sup>t</sup>* on logarithm of durability for BP-1 is presented. At predetermined operating time for this material – 105 hours (11.4 years) conventional *w cor <sup>K</sup><sup>t</sup>* obtained by extrapolating of experimental data, depending on testing medium, comprises from 0.28 to 0.11. Results of testing presented in Fig. 16 , permit to propose the following coefficients of long-term resistance of BP-1 on bending at its assumed operation in stressed state in water and in 1% solutions of caustic soda, sulphuric and nitric acids (Table15).

1 – water; 2 – H2SO4; 3 – HNO3; 4 – NaOH

practically unchanged (Fig. 15).

strength drop is continued (Fig.15).

strength limit at tension is gradually reduced and in the range of medium concentrations is

Nitric acid is a powerful oxidizer and even at low temperatures causes the breakage of the surface of phenol-formaldehyde BP, with leads to definite losses in its mass. By increasing of acid concentration the swelling of the samples of BP-2 takes place but its strength in the range of low concentrations is varied moderately. By increasing of acid concentration

**Figure 15.** Strength variation at tension of BP-2 in sulphuric (1) and nitric (2) acids

At long-term action of sulphuric acid on polyester BP the breaking of the surface of the samples of BP-1 takes place accompanying by the loss of its mass and strength reduction. True enough, this process occurs only at low concentrations (up to 5%) and in the solutions of higher concentrations the strength remains at original level. Concentrated nitric acid depending on the time of action on polyester BP, causes an intensive swelling or washing-out of the samples.

Concentration, %

The further stage of the work was the determination of long-term resistance of BP and HFRC in water and in 1 % solutions of caustic soda, sulphuric and nitric acids. Long-term resistance of BP and HFRC on bending was studied by the procedure, described in [12]. Long-term resistance of the materials, operating in water and corrosive liquid media, is nothing more nor less than the coefficient of their operating conditions, accounting the joint action of temporal factor and of water or anyone corrosive medium on the materials. For example, in fig.16, the dependence of *w cor <sup>K</sup><sup>t</sup>* on logarithm of durability for BP-1 is presented. At predetermined operating time for this material – 105 hours (11.4 years) conventional *w cor <sup>K</sup><sup>t</sup>* obtained by extrapolating of experimental data, depending on testing medium, comprises from 0.28 to 0.11. Results of testing presented in Fig. 16 , permit to propose the following coefficients of long-term resistance of BP-1 on bending at its assumed operation in stressed

Strength of BP-1 is gradually decreased by increasing of the concentration of nitric acid.

state in water and in 1% solutions of caustic soda, sulphuric and nitric acids (Table15).



**Table 15.** Coefficients of long-term resistances of BP-1 in water and in the solutions of caustic soda and acids

Processing of these and other above-presented results of investigations, for all materials, considered in this work, permitted to obtain the reference data on long-term calculated resistances of BP and HFRC. These data, by our opinion, may be beneficial at designing of structures and items by the use of BP and HFRC.

## **5. Conclusion**

At present a sufficient experience is accumulated in world practice in the field of the technology of preparation of basalt plastics and composite materials with reinforcing structures from hybrid fibers. Development of the works along this line is determined by possibility of preparation of new generation of materials with a wide spectrum of properties. Along with it, a diversity of the requirements, imposed to structural materials, tended to the fact that none of newly elaborated materials can occupy the dominant place at current stage of technology development, at least, in the immediate future. Each type of materials may be optimal in certain specific cases, as shown in presented work. A wide spectrum of needed materials, apart from considered here, may be prepared by the use of a number of reinforcing fibers with various elastic and strength characteristics and combined with carbides and oxides of the binders, as well as of reinforcing schemes which permit a purposeful control of strength, rigidity and other properties of materials.

**Section 4** 

**Catalysts and Environmental Pollution** 

**Processing Composites** 

In parallel with it, it should be noted that at present the data for physical-mechanical properties of basalt plastics and composites on the basis of hybrid fibers as well as for variation of these properties in expected operating conditions are extremely limited, which retards their use as structural materials.

We hope that the engineers of various specialties may find in this work the practical recommendations on the approach of estimation of serviceability of materials in operating media, generally, as well as the data on calculated resistances of basalt plastics and composites on the basis of hybrid reinforcing fibers, in particular.

## **Author details**

N.M. Chikhradze, L.A. Japaridze and G.S. Abashidze *G. Tsulukidze Mining Institute, Georgia* 

## **6. References**


**Catalysts and Environmental Pollution Processing Composites** 

268 Composites and Their Applications

**Author details** 

**6. References** 

355-370.

Laboratories.

512 (in Rus.).

retards their use as structural materials.

*G. Tsulukidze Mining Institute, Georgia* 

and Exhibition. Long Beach, CA.

Chemical journal. v.XIV, №2: 56-74 (in Rus.)

Traus Tech Publications, Switzerland.

with carbides and oxides of the binders, as well as of reinforcing schemes which permit a

In parallel with it, it should be noted that at present the data for physical-mechanical properties of basalt plastics and composites on the basis of hybrid fibers as well as for variation of these properties in expected operating conditions are extremely limited, which

We hope that the engineers of various specialties may find in this work the practical recommendations on the approach of estimation of serviceability of materials in operating media, generally, as well as the data on calculated resistances of basalt plastics and

[1] J. M. Park, W. G. Shin, D.J. Yoon (1999) Composites Science and Technology, v. 59, 1.3:

[2] K.E. Perepelkin (2006) Polymer fibrous composites, their main types, production

[3] P. Bronds, H. Lilhopt, A. Lystrup (2005) Composite Materials for wind power turbine

[4] D.A. Griffin (2002) SAND 2002-1879, vol. I, Albuquerquer, NM: Sandia National

[5] D.A. Griffin, T.D. Aswill (2003) Proceedings of the 48 International SAMPE Symposium

[7] E.S. Zelenski et al (2001) Reinforced plastics-modern structural materials. Russian

[8] Carbon/glass hybrids used in composite wind turbine rotor blade design. By Karen

[9] S.N. Zhurkov, E.E. Tomashevski (1959) In: Some problems of the strength of the solid.

[10] V.R. Regel et al (1974). Kinetic nature of the strength of the solid. M. , "Nauka" (in Rus.). [11] V.I. Alperin et al (1975) – In: Hand book on plastic masses. v. II, M. "Khimia", pp. 442-

[12] G.S. Abashidze, F.D.S. Marquis, N.M. Chikhradze (2007). Basalt reinforced plastics: Some operating properties. Materials Science Forum Vols. 561-565, pp. 671-674. 2007

purposeful control of strength, rigidity and other properties of materials.

composites on the basis of hybrid reinforcing fibers, in particular.

principles and properties. Chemical fibers. №1: 41-50 (in Rus.).

blades. Annual Review of Materials research, vol. 35: 505-538.

[6] D.A. Griffin (2004) SAND 2004-0073, vol. II, Sandia National Laboratories.

Fisher Mason, Contributing Writer (2004) Composites Technology.

M., Publishing Hous of Academy of Sciences of USSR, p.61-66 (in Rus.)

N.M. Chikhradze, L.A. Japaridze and G.S. Abashidze

**Chapter 11** 

© 2012 Digel et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2012 Digel et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**Heterogeneous Composites on the Basis** 

Zulkhair Mansurov, Ilya Digel, Makhmut Biisenbaev, Irina Savitskaya,

The fact that microorganisms prefer to grow on liquid/solid phase surfaces rather than in the surrounding aqueous phase was noticed long time ago [1]. Virtually any surface – animal, mineral, or vegetable – is a subject for microbial colonization and subsequent biofilm formation. It would be adequate to name just a few notorious examples on microbial colonization of contact lenses, ship hulls, petroleum pipelines, rocks in streams and all kinds of biomedical implants. The propensity of microorganisms to become surface-bound is so profound and ubiquitous that it vindicates the advantages for attached forms over their free-ranging counterparts [2]. Indeed, from ecological and evolutionary standpoints, for many microorganisms the surface-bound state means dwelling in nutritionally favorable, non-hostile environments [3]. Therefore, in most of natural and artificial ecosystems surfaceassociated microorganisms vastly outnumber organisms in suspension and often organize into complex communities with features that differ dramatically from those of free cells [4].

Initially introduced as just an imitation of Mother Nature, artificial immobilization of cells and enzymes has now transformed itself into a valuable biotechnological instrument. Its growing practical application and development over years led to appearance of fascinating novel microbial and enzymatic technologies [5-7]. Research on the immobilized biocatalysts is currently conducted in many laboratories around the world. In Japan, USA and other countries immobilized microbial cells have been successfully applied for adsorption of heavy metals from dilute solutions [8, 9], for purification of sewage [10] as well as for intensification of microbiological technologies (production of antibiotics, organic acids, sugar syrups, fermented drinks, etc.) [11]. It was shown that immobilized cells allow

**of Microbial Cells and Nanostructured** 

Aida Kistaubaeva, Nuraly Akimbekov and Azhar Zhubanova

**Carbonized Sorbents** 

http://dx.doi.org/10.5772/47796

**1. Introduction** 

Additional information is available at the end of the chapter

**Chapter 11** 

## **Heterogeneous Composites on the Basis of Microbial Cells and Nanostructured Carbonized Sorbents**

Zulkhair Mansurov, Ilya Digel, Makhmut Biisenbaev, Irina Savitskaya, Aida Kistaubaeva, Nuraly Akimbekov and Azhar Zhubanova

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/47796

## **1. Introduction**

The fact that microorganisms prefer to grow on liquid/solid phase surfaces rather than in the surrounding aqueous phase was noticed long time ago [1]. Virtually any surface – animal, mineral, or vegetable – is a subject for microbial colonization and subsequent biofilm formation. It would be adequate to name just a few notorious examples on microbial colonization of contact lenses, ship hulls, petroleum pipelines, rocks in streams and all kinds of biomedical implants. The propensity of microorganisms to become surface-bound is so profound and ubiquitous that it vindicates the advantages for attached forms over their free-ranging counterparts [2]. Indeed, from ecological and evolutionary standpoints, for many microorganisms the surface-bound state means dwelling in nutritionally favorable, non-hostile environments [3]. Therefore, in most of natural and artificial ecosystems surfaceassociated microorganisms vastly outnumber organisms in suspension and often organize into complex communities with features that differ dramatically from those of free cells [4].

Initially introduced as just an imitation of Mother Nature, artificial immobilization of cells and enzymes has now transformed itself into a valuable biotechnological instrument. Its growing practical application and development over years led to appearance of fascinating novel microbial and enzymatic technologies [5-7]. Research on the immobilized biocatalysts is currently conducted in many laboratories around the world. In Japan, USA and other countries immobilized microbial cells have been successfully applied for adsorption of heavy metals from dilute solutions [8, 9], for purification of sewage [10] as well as for intensification of microbiological technologies (production of antibiotics, organic acids, sugar syrups, fermented drinks, etc.) [11]. It was shown that immobilized cells allow

© 2012 Digel et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Digel et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

conducting biotechnological process over extended periods of time, under strict control of the process kinetics, product quality and microbial activity [12].

Heterogeneous Composites on the Basis of Microbial Cells and Nanostructured Carbonized Sorbents 273

Concerning the biocatalyst viability/activity retaining, the immobilization by adsorption is probably the gentlest existing method [14]. Because the adsorptive fixation occurs under "standard" conditions, no changes of the cultivation parameters are necessary to produce the immobilized biocatalysts. Compared to cell entrapment in organic polymers it can generally be assumed that during adsorption also the enzymatic activity can be preserved at a high level. Very often the activity of only one enzyme is responsible of the catalytic process of interest. In such a process the stability is characterized by the half-life of the enzyme.

Though adsorbed biocatalyst systems are easy to run and used for many years, there is still enough space for optimization [13]. Development and probation of new types of heterogeneous composite materials, possessing advanced properties for biological catalysts, as carrier systems, as filters etc. on the basis of attached enzymes or whole microbial cells is of great importance for biotechnological processes. These and other tasks are addressed by *engineering enzymology* – a scientific and technical discipline combining principles, theoretical approaches and practical methods of chemical and enzymatic catalysis, microbiology, chemical technology and biochemistry. Recent efforts in engineering

development and optimization of immobilization methods leading to novel

search of materials satisfying strict requirements of biotechnological processes (such as

 construction of bio-composite materials based on individual enzymes, multi-enzyme complexes and whole cells, targeted on realization of specific industrial processes; development of methods for modification of surface properties aimed on fine tuning

In the light of these challenges, nanostructured carbonized materials appear as an attractive substrate for designing and production of cost-effective high-performance bio-composite

Adsorption properties of carbonaceous adsorbents are used in purification and recovery of valuable substances for very long time. Active carbons are used in oil processing, petroleum chemistry, wine making, butter production, etc. [19-21]. They are increasingly applied in medicine, for example, to remove toxins from physiological liquids [22]. The last years are characterized by the intensive studies on carbon nanotubes and nanostructured carbon

There are many methods suitable for synthesis of NCS, such as electric arc discharge, laser vaporization and chemical vapor deposition techniques [23-25]. In the Institute of Combustion Problems (Almaty, Kazakhstan) following methods are used for obtaining of NCS: flame carbonization, catalytic carbonization and synthesis of carbon nanotubes by

Enzymatic "half-lives" up to two years have been reported [18].

enzymology are focused (among others) on the following directions:

biotechnological and biomedical applications;

and better control of the "biocatalyst-carrier" interface

**2. Synthesis of nanostructured carbonized materials** 

non-toxicity, mechanical stability, etc.);

materials.

sorbents (NCS).

Immobilization of cells can be carried out mainly by two methods: by entrapment of the microorganisms into porous polymers or microcapsules or by binding to an organic or inorganic support matrix (adsorption methods). The latter is considered to be more suitable for retaining cell viability [13]. Adsorption is also one of the easiest methods of immobilization of microbial cells, especially those that adhere naturally to the surfaces of materials [14]. It should be noted here that rapid development of technology of receipt of the immobilized biocatalysts resulted in contradictory results. So, the first attempts of immobilization were related with adsorption of enzymes and cells on arboreal sawdust and coal. In these experiments, adsorption was accompanied by a considerable desorption. In this connection, regarding the simplicity and availability of adsorption immobilization it has been having a reputation like "easy come easy go". Though never forgotten, in the last decade adsorption methods of immobilization gained increasingly more interest caused by considerable expansion in assortment of carriers with outstanding absorption properties, by better understanding of mechanisms and approaches aimed on firm attachment of biocatalyst to a carrier and by development of new methods of surface conditioning [12].

The adhesion of microbial cells to surfaces is rendered mainly by Van der Waals forces, ionic and covalent interactions, with considerable contribution of various microbial exopolymers [13]. Traditionally, adsorption immobilization is regarded as consisting of several relatively distinct stages, including a) adsorption of dissolved macromolecules on the surface; b) diffusion and concentration of cells from the bulk phase to the surface; c) reversible attachment of cells; d) biosynthesis of anchoring polymers by the cells which leads to an irreversible attachment stabilized by covalent bonds and entropy-driven interactions.

Selection of an appropriate adsorbent, especially for industrial process is based on several criteria. Most important among them are: a) material's costs and availability in large amounts; b) simplicity and efficacy of the immobilization process; c) preservation of cell viability; d) adsorbent's specific surface (capacity). There is no an ideal material so far but many these requirements are met by inorganic (sand particles, ceramics, metallic hydroxides and porous glass) and organic (charcoal, wood shavings and cellulose, polyurethanes) carriers. For example, porous glass-based fixed-bed reactors are successfully used for of the aerobic [15] and anaerobic [16] biotechnological transformations.

The immobilization process can be characterized by several parameters: initial biomass loading, retainment of biomass, strength of the adhesion, retainment of the activity of the biocatalyst, effectiveness of mass transfer, engineering realization and general operational stability. When microorganisms are immobilized by adsorption the initial cell loading of the immobilization matrix is one of the limiting factors [17]. The cell loading on the adsorbent is influenced by the physical and chemical properties of the adsorption material, of the microorganism to be immobilized and by the composition and parameters of the surrounding medium. Another critical point for a system with the cells immobilized by adsorption is the retainment of the biomass on the surface. The retainment is generally ruled by the adhesion strength, which can be described in kinetic and in thermodynamic terms.

Concerning the biocatalyst viability/activity retaining, the immobilization by adsorption is probably the gentlest existing method [14]. Because the adsorptive fixation occurs under "standard" conditions, no changes of the cultivation parameters are necessary to produce the immobilized biocatalysts. Compared to cell entrapment in organic polymers it can generally be assumed that during adsorption also the enzymatic activity can be preserved at a high level. Very often the activity of only one enzyme is responsible of the catalytic process of interest. In such a process the stability is characterized by the half-life of the enzyme. Enzymatic "half-lives" up to two years have been reported [18].

272 Composites and Their Applications

conducting biotechnological process over extended periods of time, under strict control of

Immobilization of cells can be carried out mainly by two methods: by entrapment of the microorganisms into porous polymers or microcapsules or by binding to an organic or inorganic support matrix (adsorption methods). The latter is considered to be more suitable for retaining cell viability [13]. Adsorption is also one of the easiest methods of immobilization of microbial cells, especially those that adhere naturally to the surfaces of materials [14]. It should be noted here that rapid development of technology of receipt of the immobilized biocatalysts resulted in contradictory results. So, the first attempts of immobilization were related with adsorption of enzymes and cells on arboreal sawdust and coal. In these experiments, adsorption was accompanied by a considerable desorption. In this connection, regarding the simplicity and availability of adsorption immobilization it has been having a reputation like "easy come easy go". Though never forgotten, in the last decade adsorption methods of immobilization gained increasingly more interest caused by considerable expansion in assortment of carriers with outstanding absorption properties, by better understanding of mechanisms and approaches aimed on firm attachment of biocatalyst to a carrier and by development of new methods of surface conditioning [12].

The adhesion of microbial cells to surfaces is rendered mainly by Van der Waals forces, ionic and covalent interactions, with considerable contribution of various microbial exopolymers [13]. Traditionally, adsorption immobilization is regarded as consisting of several relatively distinct stages, including a) adsorption of dissolved macromolecules on the surface; b) diffusion and concentration of cells from the bulk phase to the surface; c) reversible attachment of cells; d) biosynthesis of anchoring polymers by the cells which leads to an

Selection of an appropriate adsorbent, especially for industrial process is based on several criteria. Most important among them are: a) material's costs and availability in large amounts; b) simplicity and efficacy of the immobilization process; c) preservation of cell viability; d) adsorbent's specific surface (capacity). There is no an ideal material so far but many these requirements are met by inorganic (sand particles, ceramics, metallic hydroxides and porous glass) and organic (charcoal, wood shavings and cellulose, polyurethanes) carriers. For example, porous glass-based fixed-bed reactors are successfully used for of the

The immobilization process can be characterized by several parameters: initial biomass loading, retainment of biomass, strength of the adhesion, retainment of the activity of the biocatalyst, effectiveness of mass transfer, engineering realization and general operational stability. When microorganisms are immobilized by adsorption the initial cell loading of the immobilization matrix is one of the limiting factors [17]. The cell loading on the adsorbent is influenced by the physical and chemical properties of the adsorption material, of the microorganism to be immobilized and by the composition and parameters of the surrounding medium. Another critical point for a system with the cells immobilized by adsorption is the retainment of the biomass on the surface. The retainment is generally ruled by the adhesion strength, which can be described in kinetic and in thermodynamic terms.

irreversible attachment stabilized by covalent bonds and entropy-driven interactions.

aerobic [15] and anaerobic [16] biotechnological transformations.

the process kinetics, product quality and microbial activity [12].

Though adsorbed biocatalyst systems are easy to run and used for many years, there is still enough space for optimization [13]. Development and probation of new types of heterogeneous composite materials, possessing advanced properties for biological catalysts, as carrier systems, as filters etc. on the basis of attached enzymes or whole microbial cells is of great importance for biotechnological processes. These and other tasks are addressed by *engineering enzymology* – a scientific and technical discipline combining principles, theoretical approaches and practical methods of chemical and enzymatic catalysis, microbiology, chemical technology and biochemistry. Recent efforts in engineering enzymology are focused (among others) on the following directions:


In the light of these challenges, nanostructured carbonized materials appear as an attractive substrate for designing and production of cost-effective high-performance bio-composite materials.

## **2. Synthesis of nanostructured carbonized materials**

Adsorption properties of carbonaceous adsorbents are used in purification and recovery of valuable substances for very long time. Active carbons are used in oil processing, petroleum chemistry, wine making, butter production, etc. [19-21]. They are increasingly applied in medicine, for example, to remove toxins from physiological liquids [22]. The last years are characterized by the intensive studies on carbon nanotubes and nanostructured carbon sorbents (NCS).

There are many methods suitable for synthesis of NCS, such as electric arc discharge, laser vaporization and chemical vapor deposition techniques [23-25]. In the Institute of Combustion Problems (Almaty, Kazakhstan) following methods are used for obtaining of NCS: flame carbonization, catalytic carbonization and synthesis of carbon nanotubes by

microwave plasma enhanced chemical vapor deposition (MPECVD). It was found that the transition metals like Fe, Ni, Co, their oxides and alloys are very effective catalysts for carbon nano-structuring. Another interesting approach used was the carbonization of walnut shells, grape seeds, apricot stones, wheat bran, rice husk, etc. in presence of activating agents. The samples were carbonized according to the procedure developed in the R.M. Mansurova Laboratory of Carbon Nanomaterials at the Institute of Combustion Problems, using a gas-flow setup **(Figure 1)** within temperature range of 250–900 °C in argon flow (50–90 cm3/min).

Heterogeneous Composites on the Basis of Microbial Cells and Nanostructured Carbonized Sorbents 275

300 25 12 1.8 250 500 30 13 2.3 770 600 30 16 2.4 780 700 30 16 2.3 800 800 28 14 1.7 830 850 29 15 2.4 800

300 18 12 3 200 600 22 14 6 500 700 27 15 7 530 800 25 13 5 540 850 26 14 6 500

**Table 1.** Specific surface and pore size of the samples carbonized at different temperatures

Electron microscopy images (**Figure 2**) show the meso- and macro-porous structure of the materials appeared as a result of flame carbonization. A drastic contrast is visible between the structures of the raw material and the material after temperature treatment. Interestingly, flame carbonization of the raw plant materials often led to formation of complex carbon nanostructures (**Figure 3**) of various size and morphology. Treatment at 500°C resulted in appearance of transparent thin membrane sheets of 20-40 m size. Prolonged heating (>30 min) at 600C cased the formed translucent films to roll into 1400 nm long tubular structures of a diameter 400-500 nm. Further increase in the carbonization temperature and duration initiated the appearance of variety of nanostructures of diverse

**Figure 2.** Electron microscopic images of rice shells in native state (A) and after carbonization at 650°C (B)

**Ssp, m2/g Macropores Mesopores Micropores**

**Raw** 

**Walnut Shells** 

**Grape Stones** 

morphologies.

**Material T, °C Size, μ<sup>m</sup>**

**Figure 1.** Pilot setup for flame carbonization of diverse raw plant materials.

During carbonization the major mass loss occurred within temperature range 150-500°C, where large amount of volatile and liquid products (65-75 % of total mass) were released. In the case of rice husk, the reduction of mass was found to be around 50% which is related to high content of silicon in the samples.

## **3. Surface structure and composition of the plant-derived carbonized sorbents**

Carbon surface has a unique character. It has a porous structure which determines its high adsorption capacity; it has a chemical composition which enables numerous interactions with both polar and nonpolar molecules. Besides, it has active sites in the form of edges, dislocations and discontinuities which facilitate its chemical reactions with many compounds and functional groups.

Carbonized sorbents obtained by us on the basis of plant materials possess extended macroand mesoporous structure, favorable for the adsorption of large molecules and cells [20, 22]. One can see in the **Table 1** that the specific surface (Ssp) and size of pores increased proportionally to the carbonization temperature up to 700 °C. However, further increase of temperature caused decrease of these parameters due to the increase of the density of the samples as reported also by Banerjee and coworkers [26].


argon flow (50–90 cm3/min).

high content of silicon in the samples.

compounds and functional groups.

samples as reported also by Banerjee and coworkers [26].

**sorbents** 

microwave plasma enhanced chemical vapor deposition (MPECVD). It was found that the transition metals like Fe, Ni, Co, their oxides and alloys are very effective catalysts for carbon nano-structuring. Another interesting approach used was the carbonization of walnut shells, grape seeds, apricot stones, wheat bran, rice husk, etc. in presence of activating agents. The samples were carbonized according to the procedure developed in the R.M. Mansurova Laboratory of Carbon Nanomaterials at the Institute of Combustion Problems, using a gas-flow setup **(Figure 1)** within temperature range of 250–900 °C in

**Figure 1.** Pilot setup for flame carbonization of diverse raw plant materials.

During carbonization the major mass loss occurred within temperature range 150-500°C, where large amount of volatile and liquid products (65-75 % of total mass) were released. In the case of rice husk, the reduction of mass was found to be around 50% which is related to

**3. Surface structure and composition of the plant-derived carbonized** 

Carbon surface has a unique character. It has a porous structure which determines its high adsorption capacity; it has a chemical composition which enables numerous interactions with both polar and nonpolar molecules. Besides, it has active sites in the form of edges, dislocations and discontinuities which facilitate its chemical reactions with many

Carbonized sorbents obtained by us on the basis of plant materials possess extended macroand mesoporous structure, favorable for the adsorption of large molecules and cells [20, 22]. One can see in the **Table 1** that the specific surface (Ssp) and size of pores increased proportionally to the carbonization temperature up to 700 °C. However, further increase of temperature caused decrease of these parameters due to the increase of the density of the **Table 1.** Specific surface and pore size of the samples carbonized at different temperatures

Electron microscopy images (**Figure 2**) show the meso- and macro-porous structure of the materials appeared as a result of flame carbonization. A drastic contrast is visible between the structures of the raw material and the material after temperature treatment. Interestingly, flame carbonization of the raw plant materials often led to formation of complex carbon nanostructures (**Figure 3**) of various size and morphology. Treatment at 500°C resulted in appearance of transparent thin membrane sheets of 20-40 m size. Prolonged heating (>30 min) at 600C cased the formed translucent films to roll into 1400 nm long tubular structures of a diameter 400-500 nm. Further increase in the carbonization temperature and duration initiated the appearance of variety of nanostructures of diverse morphologies.

**Figure 2.** Electron microscopic images of rice shells in native state (A) and after carbonization at 650°C (B)

Heterogeneous Composites on the Basis of Microbial Cells and Nanostructured Carbonized Sorbents 277

**Figure 4.** Major functional groups on the surface of carbonized adsorbents: 1) phenol (hydroxyl); 2)

Functional chemical groups on the NCS were analyzed by infrared spectroscopy using IRspectrophotometer UR-20 (Zeiss Co., Germany). The IR-spectra of the native (raw) plant materials were mainly composed of characteristic absorption bands of NH2 (3431.92 cm-1), ОН (3009.97 cm-1), С=О (1643.25 cm-1), С–О (1241.55 cm-1), С–ОН (1055.64-1157.28 cm-1), С=С, С=N (1662.55 cm-1) groups (**Figure 5a**). After carbonization at temperatures of 600–850 °C, a sharp (10-fold) drop of the intensity of characteristic bands of OH and NH groups was observed. In turn, the intensity of characteristic C–O–C bands increased. Also, bands related to CO32– groups appeared and their intensity increased substantially with temperature rise. We observed also the bands related to CO2 group in the region 2486.19 cm-1 (**Figure 5b**). Carbonization of apricot stones and rice husks proceeded similarly, but the latter displayed

In general, the higher was the temperature of the carbonization process the more intense were the characteristic absorption bands of the groups of NH2, СОН, С=О, ОН as well as valence vibrations of CH-group in the aromatic rings. Furthermore, the IR-spectra obtained after carbonization exhibited characteristic absorption bands at 883 and 1050 cm-1 corresponding to С=С deformation vibrations of the aromatic ring, also those related to valence vibrations of aromatic ring 1600, 1578 and 1510 cm-1 as well as –С-Н-vibrations at 3053 and 3030 cm-1. In the sorbents carbonized at 300-850C, the following polyaromatic hydrocarbons were identified: pyrene, (due to the presence of its characteristic absorption bands at 720 and 850 cm-1); coronene: 547 and 1320 cm-1; fluoranthene: 600, 740 and 820 cm-1. Thus, we established the appearance of multiple polyaromatic hydrocarbons structures after carbonization. Further increase of carbonization temperature led to increase in intensity of

quinone (carbonyl); 3) carboxyl; 4) ester; 5) enol; 6)-8) different kinds of lactone groups.

lower intensity of the corresponding bands.

absorption bands related to aromatic condensed systems.

**Figure 3.** Diverse micro- and nanoscale structures observed with electron microscopy in apricot stones carbonized at different temperatures: (A) at 500C; (B) at 600**°**C for 30 min; (C) at 700ºC; (D) at 750°C.

Together with flame carbonization, microwave plasma-enhanced chemical vapor deposition (MPECVD) is considered to be a very promising method for the carbon nanotubes synthesis due to the lower growth temperature, uniform heat distribution and the ability to control different growth parameters [27]. Carbon nanostructures having different shapes have been synthesized using this method: aligned and curly filaments, flat and coiled carbon nanosheets. We also investigated the impact of different growth parameters such as temperature, pressure and hydrogen/methane exchange rate on the morphology of the carbon nanotubes. The results showed that there is a strong dependence of the morphology of the carbon nanotubes on the experimental conditions. For example, the quality of the carbon nanotubes was greatly affected by nitrogen influx during the growth process. Moreover, the diameter of the carbon nanotubes became smaller as nitrogen concentration in the gas mixture dropped. This implies the potential way to control the diameter of the carbon nanotubes precisely. It was also found that the threshold field required for the field emission can be reduced if nitrogen gas was introduced.

Adsorption behavior of the NCSs cannot be interpreted on the basis of surface area, pore size and nanostructural features alone. Specificity, affinity and capacity of such materials are strongly determined by chemical groups on their surface. These groups mostly appear due to controlled oxidation of carbon material's surface and can be roughly classified as phenolic (hydroxyl), carbonyl, carboxyl, ester, lactone and other groups (**Figure 4**).

**Figure 3.** Diverse micro- and nanoscale structures observed with electron microscopy in apricot stones carbonized at different temperatures: (A) at 500C; (B) at 600**°**C for 30 min; (C) at 700ºC; (D) at 750°C.

Together with flame carbonization, microwave plasma-enhanced chemical vapor deposition (MPECVD) is considered to be a very promising method for the carbon nanotubes synthesis due to the lower growth temperature, uniform heat distribution and the ability to control different growth parameters [27]. Carbon nanostructures having different shapes have been synthesized using this method: aligned and curly filaments, flat and coiled carbon nanosheets. We also investigated the impact of different growth parameters such as temperature, pressure and hydrogen/methane exchange rate on the morphology of the carbon nanotubes. The results showed that there is a strong dependence of the morphology of the carbon nanotubes on the experimental conditions. For example, the quality of the carbon nanotubes was greatly affected by nitrogen influx during the growth process. Moreover, the diameter of the carbon nanotubes became smaller as nitrogen concentration in the gas mixture dropped. This implies the potential way to control the diameter of the carbon nanotubes precisely. It was also found that the threshold field required for the field

Adsorption behavior of the NCSs cannot be interpreted on the basis of surface area, pore size and nanostructural features alone. Specificity, affinity and capacity of such materials are strongly determined by chemical groups on their surface. These groups mostly appear due to controlled oxidation of carbon material's surface and can be roughly classified as phenolic

emission can be reduced if nitrogen gas was introduced.

(hydroxyl), carbonyl, carboxyl, ester, lactone and other groups (**Figure 4**).

**Figure 4.** Major functional groups on the surface of carbonized adsorbents: 1) phenol (hydroxyl); 2) quinone (carbonyl); 3) carboxyl; 4) ester; 5) enol; 6)-8) different kinds of lactone groups.

Functional chemical groups on the NCS were analyzed by infrared spectroscopy using IRspectrophotometer UR-20 (Zeiss Co., Germany). The IR-spectra of the native (raw) plant materials were mainly composed of characteristic absorption bands of NH2 (3431.92 cm-1), ОН (3009.97 cm-1), С=О (1643.25 cm-1), С–О (1241.55 cm-1), С–ОН (1055.64-1157.28 cm-1), С=С, С=N (1662.55 cm-1) groups (**Figure 5a**). After carbonization at temperatures of 600–850 °C, a sharp (10-fold) drop of the intensity of characteristic bands of OH and NH groups was observed. In turn, the intensity of characteristic C–O–C bands increased. Also, bands related to CO32– groups appeared and their intensity increased substantially with temperature rise. We observed also the bands related to CO2 group in the region 2486.19 cm-1 (**Figure 5b**). Carbonization of apricot stones and rice husks proceeded similarly, but the latter displayed lower intensity of the corresponding bands.

In general, the higher was the temperature of the carbonization process the more intense were the characteristic absorption bands of the groups of NH2, СОН, С=О, ОН as well as valence vibrations of CH-group in the aromatic rings. Furthermore, the IR-spectra obtained after carbonization exhibited characteristic absorption bands at 883 and 1050 cm-1 corresponding to С=С deformation vibrations of the aromatic ring, also those related to valence vibrations of aromatic ring 1600, 1578 and 1510 cm-1 as well as –С-Н-vibrations at 3053 and 3030 cm-1. In the sorbents carbonized at 300-850C, the following polyaromatic hydrocarbons were identified: pyrene, (due to the presence of its characteristic absorption bands at 720 and 850 cm-1); coronene: 547 and 1320 cm-1; fluoranthene: 600, 740 and 820 cm-1. Thus, we established the appearance of multiple polyaromatic hydrocarbons structures after carbonization. Further increase of carbonization temperature led to increase in intensity of absorption bands related to aromatic condensed systems.

Heterogeneous Composites on the Basis of Microbial Cells and Nanostructured Carbonized Sorbents 279

**4. Adsorption characteristics of the nanostructured carbonized materials** 

Activated carbons are known as excellent adsorbents. Their applications include the adsorptive removal of color, odor, taste, undesirable organic and inorganic pollutants from drinking and waste water; air purification in inhabited spaces; purification of many chemical, and pharmaceutical products, etc. [19-21, 28]. Their use in medicine and health applications to combat certain types of bacterial ailments and for the adsorptive removal of certain toxins and poisons, and for purification of blood, becomes increasingly popular [29, 30]. Studies in last years have brought data on high adsorption ability of carbonized materials in respect of mammalian cells [31], microbial cells [32] and enzymes [33, 34].

The samples we used for microbial adsorption had been carbonized according to the procedure developed at the Laboratory of Hybrid Technologies in the Institute of Combustion Problems, Almaty, Kazakhstan. A flow set-up was used with following parameters: temperature range 650-800°C in argon flow (50-90 cm³/min). Different temperatures and flow regimes caused alterations in the pore structure and therefore resulted in different properties of the activated carbon [35, 36]. The adsorbents obtained from plant material showed themselves as very versatile and efficient because of their extremely high surface area, multiple functional groups and the macro-pore structure which is highly suitable for bacterial adhesion. The interaction between the cell and the adsorbing surface is dictated by multiple physicochemical variables, reviewed in many brilliant works [37-39]. Obviously, an effective attachment depends on chemical and physical properties of both adsorbent and cells. The chemical groups on the surface of the carbonized materials were mentioned in the previous section. In this respect, microbial cells demonstrate even larger versatility. Their surfaces can be hydrophilic or hydrophobic, carry positively or negatively charges; expose various specialized chemical groups and even release polymers (adhesive glycoproteins,

**Figure 6.** Principal functional groups on the surface of microbial cells: 1) phosphate; 2) amine; 3)

Molecular biological and biochemical studies on cell adhesion focus predominantly on identification, isolation and structural analysis of attachment-responsible biological molecules and their genetic determinants. Physiological aspects of cellular adsorption

**in respect of microbial cells** 

polysaccharides, proteins, teichoic acids, etc. (**Figure 6**.).

carboxyl; 4) carbonyl; 5) hydroxyl.

**Figure 5.** IR-spectra of native (non-carbonized) (A) and carbonized at 800°C (B) apricot stone surfaces.

## **4. Adsorption characteristics of the nanostructured carbonized materials in respect of microbial cells**

278 Composites and Their Applications

**Figure 5.** IR-spectra of native (non-carbonized) (A) and carbonized at 800°C (B) apricot stone surfaces.

Activated carbons are known as excellent adsorbents. Their applications include the adsorptive removal of color, odor, taste, undesirable organic and inorganic pollutants from drinking and waste water; air purification in inhabited spaces; purification of many chemical, and pharmaceutical products, etc. [19-21, 28]. Their use in medicine and health applications to combat certain types of bacterial ailments and for the adsorptive removal of certain toxins and poisons, and for purification of blood, becomes increasingly popular [29, 30]. Studies in last years have brought data on high adsorption ability of carbonized materials in respect of mammalian cells [31], microbial cells [32] and enzymes [33, 34].

The samples we used for microbial adsorption had been carbonized according to the procedure developed at the Laboratory of Hybrid Technologies in the Institute of Combustion Problems, Almaty, Kazakhstan. A flow set-up was used with following parameters: temperature range 650-800°C in argon flow (50-90 cm³/min). Different temperatures and flow regimes caused alterations in the pore structure and therefore resulted in different properties of the activated carbon [35, 36]. The adsorbents obtained from plant material showed themselves as very versatile and efficient because of their extremely high surface area, multiple functional groups and the macro-pore structure which is highly suitable for bacterial adhesion.

The interaction between the cell and the adsorbing surface is dictated by multiple physicochemical variables, reviewed in many brilliant works [37-39]. Obviously, an effective attachment depends on chemical and physical properties of both adsorbent and cells. The chemical groups on the surface of the carbonized materials were mentioned in the previous section. In this respect, microbial cells demonstrate even larger versatility. Their surfaces can be hydrophilic or hydrophobic, carry positively or negatively charges; expose various specialized chemical groups and even release polymers (adhesive glycoproteins, polysaccharides, proteins, teichoic acids, etc. (**Figure 6**.).

**Figure 6.** Principal functional groups on the surface of microbial cells: 1) phosphate; 2) amine; 3) carboxyl; 4) carbonyl; 5) hydroxyl.

Molecular biological and biochemical studies on cell adhesion focus predominantly on identification, isolation and structural analysis of attachment-responsible biological molecules and their genetic determinants. Physiological aspects of cellular adsorption

concern mainly the influence of cultivation parameters (temperature, nutrition compounds, oxygen concentration, presence of antibiotics and vitamins) on bacterial adherence-related phenotype, adhesion molecules metabolism and surface structural organization [40]. Once in initial contact with a surface, microbes develop different types of attachment behaviors. Motile attachment behavior of *P. fluorescens* allows the flagellated cells to move along surfaces in a semi-attached condition within the hydrodynamic boundary layer, independent of the flow direction [41]. Reversible adhesion of *E. coli* cells with residence times of over several minutes on a surface has been described as "near-surface swimming"[42]. In the case that microbes can no longer move perpendicularly away from the surface the term "irreversible attachment" is used [14].

Heterogeneous Composites on the Basis of Microbial Cells and Nanostructured Carbonized Sorbents 281

Electron microscopy examinations suggested that there is strong bonding interaction between microbial cells and the NCSs. In case of optimal incubation parameters, the cell load reaches 62 %, corresponding to 108 colony-forming units (viable cells) per gram of NCS. The microbial cells were distributed on the surfaces not homogenously but rather formed clusters (micro-colonies). Taking into consideration potential intestinal and biomedical applications of the bio-composites, this fact is of particular importance because inter-cellular interactions and aggregation processes in the micro-colonies point out initial stages of biofilm formation, which in turn is an essential factor for bacterial survival and

**Figure 8** shows subsequent stages of rice husk colonization by Lactobacilli. It is clearly visible that the number of cells in a micro-colony varies between around 20 and 200 corresponding to the natural micro-colony structure in the epithelial layer of the intestine. The appeared bacterial colonies demonstrated almost irreversible adhesion in the absence of

**Figure 8.** Subsequent stages of colonization of NCSs by Lactobacilli. A: carbonized rice husk, initial adsorption; B: carbonized grape stones, initial adsorption, C and D – carbonized grape stones, micro-

adaptability.

colony formation

a competitive substrate (intestinal surface).

A net electrostatic charge on the NCS and the cell surfaces affects the distribution of ions in the surrounding interfacial region, resulting in an increased concentration of counter ions (ions of opposite charge to that of the particle) close to the surface that results in the formation of an electric double layer. This layer consists of two parts: an inner region (Stern layer) where the ions are strongly bound and an outer (diffuse) region where they are less firmly associated.

Thermodynamically, spontaneous cell adsorption onto a surface results in decrease of Gibbs free energy but sometimes there is a significant energy barrier due to electrostatic repulsion. Existing theoretical models predict that there are two regions where the strongest attraction forces between two surfaces occur (the "primary" and "secondary" minima, at distances of 0.5 nm and ~5 nm, correspondingly). Generally it is assumed that microbes adhere reversibly to the "secondary minimum" and irreversibly to the "primary minimum" with the aid of cell surface appendages that can pierce the repulsive energy barrier [12, 14].

Our previous experiments have shown that, together with electrostatic properties, the hydrophobicity of both cells and NCSs plays a crucial role in both adsorption capacity and biomass retainment on the surface. Hydrophobicity of the carbonized materials can be easily controlled by the activation of the surfaces by water steam. The nature of the exposed chemical groups enables formation of multiple covalent bonds between the surfaces (**Figure 7**). Large number of different interactions involved in the cellular attachment to the carbonized surfaces makes possible fine tuning of the immobilization process in order to achieve versatility and adaptability of the bio-composite materials for different applications.

**Figure 7.** Formation of covalent bonds between the surfaces of microbial cells and the carbonized materials considerably contributes to stability of the bio-composite materials.

Electron microscopy examinations suggested that there is strong bonding interaction between microbial cells and the NCSs. In case of optimal incubation parameters, the cell load reaches 62 %, corresponding to 108 colony-forming units (viable cells) per gram of NCS. The microbial cells were distributed on the surfaces not homogenously but rather formed clusters (micro-colonies). Taking into consideration potential intestinal and biomedical applications of the bio-composites, this fact is of particular importance because inter-cellular interactions and aggregation processes in the micro-colonies point out initial stages of biofilm formation, which in turn is an essential factor for bacterial survival and adaptability.

280 Composites and Their Applications

concern mainly the influence of cultivation parameters (temperature, nutrition compounds, oxygen concentration, presence of antibiotics and vitamins) on bacterial adherence-related phenotype, adhesion molecules metabolism and surface structural organization [40]. Once in initial contact with a surface, microbes develop different types of attachment behaviors. Motile attachment behavior of *P. fluorescens* allows the flagellated cells to move along surfaces in a semi-attached condition within the hydrodynamic boundary layer, independent of the flow direction [41]. Reversible adhesion of *E. coli* cells with residence times of over several minutes on a surface has been described as "near-surface swimming"[42]. In the case that microbes can no longer move perpendicularly away from

A net electrostatic charge on the NCS and the cell surfaces affects the distribution of ions in the surrounding interfacial region, resulting in an increased concentration of counter ions (ions of opposite charge to that of the particle) close to the surface that results in the formation of an electric double layer. This layer consists of two parts: an inner region (Stern layer) where the ions are strongly bound and an outer (diffuse) region where they are less firmly associated.

Thermodynamically, spontaneous cell adsorption onto a surface results in decrease of Gibbs free energy but sometimes there is a significant energy barrier due to electrostatic repulsion. Existing theoretical models predict that there are two regions where the strongest attraction forces between two surfaces occur (the "primary" and "secondary" minima, at distances of 0.5 nm and ~5 nm, correspondingly). Generally it is assumed that microbes adhere reversibly to the "secondary minimum" and irreversibly to the "primary minimum" with the aid of cell surface appendages that can pierce the repulsive energy barrier [12, 14].

Our previous experiments have shown that, together with electrostatic properties, the hydrophobicity of both cells and NCSs plays a crucial role in both adsorption capacity and biomass retainment on the surface. Hydrophobicity of the carbonized materials can be easily controlled by the activation of the surfaces by water steam. The nature of the exposed chemical groups enables formation of multiple covalent bonds between the surfaces (**Figure 7**). Large number of different interactions involved in the cellular attachment to the carbonized surfaces makes possible fine tuning of the immobilization process in order to achieve versatility and adaptability of the bio-composite materials for different applications.

**Figure 7.** Formation of covalent bonds between the surfaces of microbial cells and the carbonized

materials considerably contributes to stability of the bio-composite materials.

the surface the term "irreversible attachment" is used [14].

**Figure 8** shows subsequent stages of rice husk colonization by Lactobacilli. It is clearly visible that the number of cells in a micro-colony varies between around 20 and 200 corresponding to the natural micro-colony structure in the epithelial layer of the intestine. The appeared bacterial colonies demonstrated almost irreversible adhesion in the absence of a competitive substrate (intestinal surface).

**Figure 8.** Subsequent stages of colonization of NCSs by Lactobacilli. A: carbonized rice husk, initial adsorption; B: carbonized grape stones, initial adsorption, C and D – carbonized grape stones, microcolony formation

## **5. Performance of bio-composite carbonized materials in probiotic applications**

In our model experiments in vitro, NCSs showed outstanding compatibility with many bacterial strains, indicating their high potential in miscellaneous branches of biotechnology and medicine. One of such applications of great interest is design and approbation of new generation of probiotic preparations for preventions and correction of micro-ecological disorders in gastrointestinal tract of the humans and animals. Environmentally, nutritionally and infection-induced pathologic shifts of gastrointestinal tracts' micro-ecology often lead to the increase in amount of gram negative bacteria, particularly of *Enterobacteria*. It leads to the translocation of bacterial toxic products from bowels to other organs causing development of endotoxinemia and other pathologies.

Heterogeneous Composites on the Basis of Microbial Cells and Nanostructured Carbonized Sorbents 283

capsules and in liquid form without observing statistically significant difference in bacterial survival [46]. A specially designed tube with a reservoir containing probiotics has been suggested by Çaglar et al [47] with some encouraging results*.* However, the search for most suitable means of delivery and dosages of probiotics continues. One of our aims in this respect was to investigate the capacity of the carbonized materials as protective media for

The type strain of lactic acid bacteria, *Lactobacillus fermentum AK-2* was used in our probiotic studies. It possesses excellent probiotic potencies due to its high antagonistic and adhesive activities. Rice husk and grapes stones carbonized were produced in the Institute of Combustion Problems at the al-Farabi Kazakh National University in Almaty as described above. *Lactobacillus* cells were adsorbed onto the carrier for 24 hours. Unattached cells were rinsed away by the isotonic NaCl solution and the firmly attached bacteria were incubated for several more days for micro-colony formation. After that the prepared bio-composite

In bacteria survival experiments, gastric conditions were modeled in vitro by using gastric juice received from clinical gastroscopy. Different preparations of *L. fermentum* in MRS-1 medium were incubated in the gastric juice for 1 hour. After that the number of viable cells

In vivo experiments were conducted on 6-8 week old wild rats, previously subjected to an experimental dysbacteriosis induced by the antibiotic ciprofloxacin. The animals were divided into several experimental groups. The control group received only the antibiotic in therapeutic dose of 5 mg/ kg body mass; the first group, in addition, was fed with liquid suspension of *L. fermentum* AK-2; the second and the third groups received, after the induced dysbacteriosis, the same amounts of *L. fermentum* but the bacteria were

As an indicator of the probiotic activity, the number of viable *Enterobacteria* in different parts of the rat intestine was measured. Changes in detected amounts of gram-negative *Enterobacteria* such as *Escherichia coli, Klebsiella pneumoniae, Proteus vulgaris, Proteus mirabilis, Enterobacter aerogenes, Salmonella typhimurium, Shigella zonnei* and *Shigella fleexneri* were considered as a measure of the antagonistic action strength of the preparations. For *Enterobacteria* quantification, suspended gut content was incubated on Petri dishes with Endo agar. The analyses were conducted for 15 days, every day starting from a day of antibiotic treatment. Finally, the amount of *Lactobacillus* cells attached to the rat intestinal

Twenty four hours after immobilization *Lactobacillus* displayed very good growth rate and began forming micro-colonies on the NCS. The data on gastric juice resistance of suspended

material was examined microscopically to ensure successful settlement of bacteria.

immobilized on grape stones and rice husk, correspondingly.

epithelium was directly counted as described elsewhere [48].

and immobilized preparations of *Lactobacillus* are shown in **Table 2.**

probiotic bacteria immobilized in their pores.

**6. Biological objects** 

was quantified.

**7. Results** 

Probiotic is a viable mono- or mixed culture of beneficial microorganisms applied to animals or humans that sustainably improves properties of the indigenous microflora. The term "probiotics" was first coined by Lilley and Stillwell in 1965 [43]. R. Fuller later defined probiotics as "A live microbial feed supplement which beneficially affects the host animal by improving its intestinal microbial balance." [44]. Over years, the term "probiotics" has undergone several more definitions arriving at the final one, officially adopted by the International Scientific Association for Probiotics and Prebiotics, outlining the breadth and scope of probiotics as they are known today: "Live microorganisms, which when administered in adequate amounts, confer a health benefit on the host" [45]. Mechanisms of probiotic action are numerous and include:


Over past decades, probiotics have been extensively studied for their health-promoting effects and have been successfully used to control gastro-intestinal diseases. As shown above, the mechanisms of probiotic action appear to link with colonization resistance and immune modulation. Since *Bifidobacterium* and *Lactobacillus* species belong to normal intestinal microflora of humans, majority of probiotics was created on the basis of these bacteria. Lactic acid bacteria can produce numerous antimicrobial components such as organic acids, hydrogen peroxide, carbon peroxide, diacetyl, bacteriocins, as well as adhesion inhibitors, which strongly affect microflora.

Many probiotic preparations serve for an improvement of micro-ecological situations in bowels. Therefore, to reach the destination place, probiotic preparations have to pass through the stomach and the small intestine, which is unavoidably connected with significant reduction probiotic bacteria viability. To reduce this undesirable effect, several approaches have been suggested so far. Montalto et al. administered probiotic mix both in capsules and in liquid form without observing statistically significant difference in bacterial survival [46]. A specially designed tube with a reservoir containing probiotics has been suggested by Çaglar et al [47] with some encouraging results*.* However, the search for most suitable means of delivery and dosages of probiotics continues. One of our aims in this respect was to investigate the capacity of the carbonized materials as protective media for probiotic bacteria immobilized in their pores.

## **6. Biological objects**

282 Composites and Their Applications

of endotoxinemia and other pathologies.

probiotic action are numerous and include:

Prevention of adhesion of pathogen to host tissues;

adhesion inhibitors, which strongly affect microflora.

**applications** 

**5. Performance of bio-composite carbonized materials in probiotic** 

In our model experiments in vitro, NCSs showed outstanding compatibility with many bacterial strains, indicating their high potential in miscellaneous branches of biotechnology and medicine. One of such applications of great interest is design and approbation of new generation of probiotic preparations for preventions and correction of micro-ecological disorders in gastrointestinal tract of the humans and animals. Environmentally, nutritionally and infection-induced pathologic shifts of gastrointestinal tracts' micro-ecology often lead to the increase in amount of gram negative bacteria, particularly of *Enterobacteria*. It leads to the translocation of bacterial toxic products from bowels to other organs causing development

Probiotic is a viable mono- or mixed culture of beneficial microorganisms applied to animals or humans that sustainably improves properties of the indigenous microflora. The term "probiotics" was first coined by Lilley and Stillwell in 1965 [43]. R. Fuller later defined probiotics as "A live microbial feed supplement which beneficially affects the host animal by improving its intestinal microbial balance." [44]. Over years, the term "probiotics" has undergone several more definitions arriving at the final one, officially adopted by the International Scientific Association for Probiotics and Prebiotics, outlining the breadth and scope of probiotics as they are known today: "Live microorganisms, which when administered in adequate amounts, confer a health benefit on the host" [45]. Mechanisms of

Stimulation and modulation of the mucosal immune system by reducing the production

Many probiotic preparations serve for an improvement of micro-ecological situations in bowels. Therefore, to reach the destination place, probiotic preparations have to pass through the stomach and the small intestine, which is unavoidably connected with significant reduction probiotic bacteria viability. To reduce this undesirable effect, several approaches have been suggested so far. Montalto et al. administered probiotic mix both in

 Improvement of intestinal barrier integrity and up-regulation of mucin production; Killing or inhibiting the growth of pathogens through the production of bactriocins or other products such as acids or peroxides, which are antagonistic toward pathogenic bacteria. Over past decades, probiotics have been extensively studied for their health-promoting effects and have been successfully used to control gastro-intestinal diseases. As shown above, the mechanisms of probiotic action appear to link with colonization resistance and immune modulation. Since *Bifidobacterium* and *Lactobacillus* species belong to normal intestinal microflora of humans, majority of probiotics was created on the basis of these bacteria. Lactic acid bacteria can produce numerous antimicrobial components such as organic acids, hydrogen peroxide, carbon peroxide, diacetyl, bacteriocins, as well as

of pro-inflammatory cytokines through action on NF-kB pathways;

The type strain of lactic acid bacteria, *Lactobacillus fermentum AK-2* was used in our probiotic studies. It possesses excellent probiotic potencies due to its high antagonistic and adhesive activities. Rice husk and grapes stones carbonized were produced in the Institute of Combustion Problems at the al-Farabi Kazakh National University in Almaty as described above. *Lactobacillus* cells were adsorbed onto the carrier for 24 hours. Unattached cells were rinsed away by the isotonic NaCl solution and the firmly attached bacteria were incubated for several more days for micro-colony formation. After that the prepared bio-composite material was examined microscopically to ensure successful settlement of bacteria.

In bacteria survival experiments, gastric conditions were modeled in vitro by using gastric juice received from clinical gastroscopy. Different preparations of *L. fermentum* in MRS-1 medium were incubated in the gastric juice for 1 hour. After that the number of viable cells was quantified.

In vivo experiments were conducted on 6-8 week old wild rats, previously subjected to an experimental dysbacteriosis induced by the antibiotic ciprofloxacin. The animals were divided into several experimental groups. The control group received only the antibiotic in therapeutic dose of 5 mg/ kg body mass; the first group, in addition, was fed with liquid suspension of *L. fermentum* AK-2; the second and the third groups received, after the induced dysbacteriosis, the same amounts of *L. fermentum* but the bacteria were immobilized on grape stones and rice husk, correspondingly.

As an indicator of the probiotic activity, the number of viable *Enterobacteria* in different parts of the rat intestine was measured. Changes in detected amounts of gram-negative *Enterobacteria* such as *Escherichia coli, Klebsiella pneumoniae, Proteus vulgaris, Proteus mirabilis, Enterobacter aerogenes, Salmonella typhimurium, Shigella zonnei* and *Shigella fleexneri* were considered as a measure of the antagonistic action strength of the preparations. For *Enterobacteria* quantification, suspended gut content was incubated on Petri dishes with Endo agar. The analyses were conducted for 15 days, every day starting from a day of antibiotic treatment. Finally, the amount of *Lactobacillus* cells attached to the rat intestinal epithelium was directly counted as described elsewhere [48].

## **7. Results**

Twenty four hours after immobilization *Lactobacillus* displayed very good growth rate and began forming micro-colonies on the NCS. The data on gastric juice resistance of suspended and immobilized preparations of *Lactobacillus* are shown in **Table 2.**


Heterogeneous Composites on the Basis of Microbial Cells and Nanostructured Carbonized Sorbents 285

suppression in *Enterobacteria* proliferation and spread. Being immobilized on NCS, probiotic bacteria effectively inhibited growth of unhealthy bacterial forms, this counteracting development of dysbacteriosis. The measured inhibitory effects were much higher than those shown by suspended probiotic preparation. This effect can have been brought by different mechanisms, including better survival of probiotic bacteria (as was demonstrated above), by their increased antagonistic metabolic activity, and possibly also by exchange of

The possibility that some exchange between the cells adsorbed in different locations indeed could take place has been demonstrated by counting of lactic acid bacteria cells attached on the surface of intestinal epithelium after NCS-adsorbed *Lactobacillus* cells were brought in

**Figure 9.** Colonization of cultured intestinal epithelial cells by Lactobacillus initially immobilized on

As shown in the Figure 9, increase in concentration of the applied bio-composite material resulted in corresponding rise in the number of *Lactobacillus* cells firmly attached to the intestinal epithelium. Most active adhesion of probiotic cells occurs within the first two hours of incubation. Our calculations also showed that around 50% of the cells detached from the carbonized adsorbent later strongly attach to the surface of the epithelial cells. Since attachment to the recipient's cells is one of the most important indicators of a probiotic preparation activity, the obtained data suggest that the created bio-composite probiotic

We suppose that all the above-mentioned mechanisms (better survival, shifts in physiological activity, etc.) could contribute to the increased activity of immobilized probiotic strains. Our previous data suggest that the immobilization of *Lactobacillus* on carbonized materials (rice husk, grape stones) increased their physiological activity and the quantity of the antibacterial metabolites by 25-60%, which consequently would lead

the carbonized rice husk as a function of the applied bio-composite material.

preparations successfully performed their functions.

the bacteria adsorbed on NCS and the bacteria attached to the intestinal cell walls.

contact with cultured intestinal cells (**Figure 9**).

**Table 2.** Influence of in-vitro gastric juice treatment on viability of suspended and immobilized cells of Lactobacillus fermentum AK-2

In the suspended *Lactobacillus* culture after the gastric juice treatment the concentration of living cells decreased more than 7000 times. In contrast to that, the cells being a part of the bio-composite materials showed significantly (500 times) better survival rate. The obtained data strongly suggested the protective action of NCSs on the immobilized *Lactobacillus* cells. These results look very encouraging in respect of construction of highly efficient biocomposite materials having extended probiotic activities.

The next series of experiments was devoted to comparative analysis of the antagonistic activity of suspended and immobilized probiotic preparations. After induced dysbacteriosis, intestinal microflora of rats was observed for the period of 15 days. The data are presented in the **Table 3**.


\*GS: grape stone based carbonized adsorbent, \*\*RH: rice husk-based carbonized adsorbent.

**Table 3.** Influence of the probiotic bio-composites containing L. fermentum АК-2 on the quantity of Enterobacteria in the intestine of rats after ciprofloxacin-induced dysbacteriosis.

The data in the table show that after ciprofloxacin-induced dysbacteriosis, significant increase (2 orders) of the undesirable *Enterobacteria-*group microflora was observed, manifesting even more during the following 15 days after the antibiotic administration. This occurred both in the gut lumen and in its walls. Application of probiotics in the biocomposite forms, using carbonized rice husk and carbonized grape stones led to significant suppression in *Enterobacteria* proliferation and spread. Being immobilized on NCS, probiotic bacteria effectively inhibited growth of unhealthy bacterial forms, this counteracting development of dysbacteriosis. The measured inhibitory effects were much higher than those shown by suspended probiotic preparation. This effect can have been brought by different mechanisms, including better survival of probiotic bacteria (as was demonstrated above), by their increased antagonistic metabolic activity, and possibly also by exchange of the bacteria adsorbed on NCS and the bacteria attached to the intestinal cell walls.

284 Composites and Their Applications

Lactobacillus fermentum AK-2

in the **Table 3**.

Experimental group

composite materials having extended probiotic activities.

Experimental group Concentration of viable cells, ml-1

Suspended culture 3.7 109 5.2 105

**Table 2.** Influence of in-vitro gastric juice treatment on viability of suspended and immobilized cells of

In the suspended *Lactobacillus* culture after the gastric juice treatment the concentration of living cells decreased more than 7000 times. In contrast to that, the cells being a part of the bio-composite materials showed significantly (500 times) better survival rate. The obtained data strongly suggested the protective action of NCSs on the immobilized *Lactobacillus* cells. These results look very encouraging in respect of construction of highly efficient bio-

The next series of experiments was devoted to comparative analysis of the antagonistic activity of suspended and immobilized probiotic preparations. After induced dysbacteriosis, intestinal microflora of rats was observed for the period of 15 days. The data are presented

**Before treatment with ciprofloxacin** The control (3.0±0.3) 104 (6.9±0.7) 106 (1.1±0.2)102 (1.5±0.4)103 **1 day after treatment with ciprofloxacin** Without probiotics (2.9±0.5) 105 (7.9±0.6) 107 (2.9±0.3) 104 (1.2±0.4) 105 Probiotics on GS\* (9.7±0.6) 104 (1.2±0.3) 107 (7.8±0.8) 102 (8.9±0.2) 103 Probiotics on RH\*\* (6.9±0.4) 104 (9.5±0.2) 106 (0.9±0.3) 102 (5.3±0.8) 103 **15 days after treatment with ciprofloxacin** Without probiotics (2.4±0.4) 105 (2.1±0.3) 108 (8.4±0.2) 104 (9.5±0.8) 105 Probiotics on GS\* (1.2±0.7) 105 (9.6±0.6) 107 (2.9±0.4) 103 (2.8±0.4) 104 Probiotics on RH\*\* (3.4±0.4) 104 (8.5±0.7) 106 (1.2±0.3) 103 (1.2±0.7) 103

**Table 3.** Influence of the probiotic bio-composites containing L. fermentum АК-2 on the quantity of

The data in the table show that after ciprofloxacin-induced dysbacteriosis, significant increase (2 orders) of the undesirable *Enterobacteria-*group microflora was observed, manifesting even more during the following 15 days after the antibiotic administration. This occurred both in the gut lumen and in its walls. Application of probiotics in the biocomposite forms, using carbonized rice husk and carbonized grape stones led to significant

\*GS: grape stone based carbonized adsorbent, \*\*RH: rice husk-based carbonized adsorbent.

Enterobacteria in the intestine of rats after ciprofloxacin-induced dysbacteriosis.

Number of bacteria in 1g Large intestine Small intestine wall lumen wall lumen

Grape stone-based bio-composite 1.6 109 3.1 106 Rice husk-based bio-composite 1.1 109 8.2 107

Before treatment After treatment

The possibility that some exchange between the cells adsorbed in different locations indeed could take place has been demonstrated by counting of lactic acid bacteria cells attached on the surface of intestinal epithelium after NCS-adsorbed *Lactobacillus* cells were brought in contact with cultured intestinal cells (**Figure 9**).

**Figure 9.** Colonization of cultured intestinal epithelial cells by Lactobacillus initially immobilized on the carbonized rice husk as a function of the applied bio-composite material.

As shown in the Figure 9, increase in concentration of the applied bio-composite material resulted in corresponding rise in the number of *Lactobacillus* cells firmly attached to the intestinal epithelium. Most active adhesion of probiotic cells occurs within the first two hours of incubation. Our calculations also showed that around 50% of the cells detached from the carbonized adsorbent later strongly attach to the surface of the epithelial cells. Since attachment to the recipient's cells is one of the most important indicators of a probiotic preparation activity, the obtained data suggest that the created bio-composite probiotic preparations successfully performed their functions.

We suppose that all the above-mentioned mechanisms (better survival, shifts in physiological activity, etc.) could contribute to the increased activity of immobilized probiotic strains. Our previous data suggest that the immobilization of *Lactobacillus* on carbonized materials (rice husk, grape stones) increased their physiological activity and the quantity of the antibacterial metabolites by 25-60%, which consequently would lead to increase of the antagonistic activity of *Lactobacillus*. High in-vitro and in-vivo efficiency of the immobilized probiotics can be also ascribed by the specific microenvironmental physicochemical conditions on the interface "sorbent/microbe" [14]. Moreover, besides delivery of bacteria in intestine the NCSs can possibly contribute to detoxification by absorption of intestinal toxins by the active sites on the surface not occupied by microbial cells. All these considerations suggest synergistic summation of multiple beneficial effects.

Heterogeneous Composites on the Basis of Microbial Cells and Nanostructured Carbonized Sorbents 287

behavior as a component of bio-composite materials. *Spirulina platensis* is a blue-green alga (photosynthesizing cyanobacterium) having diverse biological activities. Due to high content of highly valuable proteins, indispensable amino acids, vitamins, beta-carotene and other pigments, mineral substances, indispensable fatty acids and polysaccharides, *Spirulina* has been found suitable for use as bioactive additive [49]. *Spirulina* produces an immunestimulating effect by enhancing the resistance of humans, mammals, chickens and fish to infections, has capacity of influencing hemopoiesis, stimulating the production of antibodies and cytokines [50]. Moreover, *Spirulina* preparations are regarded as functional products contributing to the preservation of the resident intestinal microflora, especially lactic acid bacilli and bifidobacteria, and to a decrease in the level of undesirable microorganisms like

In our experiments, both NCSs and *Spirulina* cells (the strain СALU-532m) applied alone to cultured rat epithelial cells, (IEC-6) at concentrations 5-50 µg/mL stimulated their proliferation and regeneration (**Figure 10**). Remarkably, being combined together in a biocomposite material, they showed a distinct synergy in their action, seemingly enhancing

**Figure 10.** Stimulation of growth of cultured intestinal epithelial rat cells by carbonized materials (rice

The epithelial cells treated by the NCS-Spirulina bio-composite reached confluence after 30 hours of incubation, whereas the control group required 48 h. The number of viable cells per

square centimeter was found to be 9100±4.6 (SD) and 8180±3.5(SD), respectively.

husk) and Spirulina platensis cells applied alone and in combination.

*Candida albicans* [51].

each other's activities.

The collected evidences clearly demonstrate that the use of the nano-structured carbonized sorbents as delivery vehicles for the oral administration of probiotic microorganisms has a very big potential for improving functionality, safety and stability of probiotic preparations. A novel probiotic preparation named "Riso-Lact" has been recently developed at the al-Farabi Kazakh National University. The preparation consists of the *Lactobacillus fermentum AK-2* cells immobilized on rice husk under well-defined optimized laboratory conditions and will possibly find its application in treatment of dysbacteriosis in humans and animals. The great binding strength and capacity of the material in respect of cells and dissolved compounds are mainly conditioned by the extended network of nanotubes but appears also due to high hydrophobicity of the surface. Although many more studies and tests are necessary, and a lot of work needs yet to be done, we can now envision the creation of a new generation of NCS-based probiotic preparations, effectively normalizing the intestinal microflora, bringing relief to millions of patients around the world.

## **8. Future prospects for biomedical and environmental engineering applications**

In the finalizing part of this chapter we would like to give a short overview of possible further applications of the bio-composite materials based of nanostructured carbonized adsorbents. Without any doubt, the field of future applications of such materials is vast and hardly foreseeable. The topics presented bellow will underline mostly biomedical and environmental applications where certain preliminary experimental material has been collected by our and other working groups.

## **8.1. Bio-composite material on the basis of carbonized rice husk and micro-algae**  *Spirulina*

As we have shown above, NCSs with immobilized *Lactobacillus* cells have a good potential as future probiotic preparations. One of key elements of their probiotic action is the involvement of the immobilized cells into the physiological processes on the surface of the intestinal epithelium. The NCS themselves also are able to adsorb significant amounts of gram-negative cells and their toxins, thus contributing to the beneficial effects of the preparations.

Together with known probiotic strains, we have recently attempted to apply the approaches previously had been probed on *Lactobacillus*, on micro-algae *Spirulina* in order to check its behavior as a component of bio-composite materials. *Spirulina platensis* is a blue-green alga (photosynthesizing cyanobacterium) having diverse biological activities. Due to high content of highly valuable proteins, indispensable amino acids, vitamins, beta-carotene and other pigments, mineral substances, indispensable fatty acids and polysaccharides, *Spirulina* has been found suitable for use as bioactive additive [49]. *Spirulina* produces an immunestimulating effect by enhancing the resistance of humans, mammals, chickens and fish to infections, has capacity of influencing hemopoiesis, stimulating the production of antibodies and cytokines [50]. Moreover, *Spirulina* preparations are regarded as functional products contributing to the preservation of the resident intestinal microflora, especially lactic acid bacilli and bifidobacteria, and to a decrease in the level of undesirable microorganisms like *Candida albicans* [51].

286 Composites and Their Applications

multiple beneficial effects.

**applications** 

*Spirulina*

preparations.

collected by our and other working groups.

to increase of the antagonistic activity of *Lactobacillus*. High in-vitro and in-vivo efficiency of the immobilized probiotics can be also ascribed by the specific microenvironmental physicochemical conditions on the interface "sorbent/microbe" [14]. Moreover, besides delivery of bacteria in intestine the NCSs can possibly contribute to detoxification by absorption of intestinal toxins by the active sites on the surface not occupied by microbial cells. All these considerations suggest synergistic summation of

The collected evidences clearly demonstrate that the use of the nano-structured carbonized sorbents as delivery vehicles for the oral administration of probiotic microorganisms has a very big potential for improving functionality, safety and stability of probiotic preparations. A novel probiotic preparation named "Riso-Lact" has been recently developed at the al-Farabi Kazakh National University. The preparation consists of the *Lactobacillus fermentum AK-2* cells immobilized on rice husk under well-defined optimized laboratory conditions and will possibly find its application in treatment of dysbacteriosis in humans and animals. The great binding strength and capacity of the material in respect of cells and dissolved compounds are mainly conditioned by the extended network of nanotubes but appears also due to high hydrophobicity of the surface. Although many more studies and tests are necessary, and a lot of work needs yet to be done, we can now envision the creation of a new generation of NCS-based probiotic preparations, effectively normalizing the intestinal

microflora, bringing relief to millions of patients around the world.

**8. Future prospects for biomedical and environmental engineering** 

In the finalizing part of this chapter we would like to give a short overview of possible further applications of the bio-composite materials based of nanostructured carbonized adsorbents. Without any doubt, the field of future applications of such materials is vast and hardly foreseeable. The topics presented bellow will underline mostly biomedical and environmental applications where certain preliminary experimental material has been

**8.1. Bio-composite material on the basis of carbonized rice husk and micro-algae** 

As we have shown above, NCSs with immobilized *Lactobacillus* cells have a good potential as future probiotic preparations. One of key elements of their probiotic action is the involvement of the immobilized cells into the physiological processes on the surface of the intestinal epithelium. The NCS themselves also are able to adsorb significant amounts of gram-negative cells and their toxins, thus contributing to the beneficial effects of the

Together with known probiotic strains, we have recently attempted to apply the approaches previously had been probed on *Lactobacillus*, on micro-algae *Spirulina* in order to check its In our experiments, both NCSs and *Spirulina* cells (the strain СALU-532m) applied alone to cultured rat epithelial cells, (IEC-6) at concentrations 5-50 µg/mL stimulated their proliferation and regeneration (**Figure 10**). Remarkably, being combined together in a biocomposite material, they showed a distinct synergy in their action, seemingly enhancing each other's activities.

**Figure 10.** Stimulation of growth of cultured intestinal epithelial rat cells by carbonized materials (rice husk) and Spirulina platensis cells applied alone and in combination.

The epithelial cells treated by the NCS-Spirulina bio-composite reached confluence after 30 hours of incubation, whereas the control group required 48 h. The number of viable cells per square centimeter was found to be 9100±4.6 (SD) and 8180±3.5(SD), respectively.

## **8.2. Nanostructured carbonized materials for treatment of chronic wounds and sores**

Heterogeneous Composites on the Basis of Microbial Cells and Nanostructured Carbonized Sorbents 289

Our studies have demonstrated that the use of NCS indeed can develop into an outstanding method for stimulation of wound healing. We produced in rats infected injuries, which healing typically occurs in 10-12 days. In the case the NCS were applied directly after the injury, an improvement and acceleration in wound healing was systematically observed

**Figure 12.** Dynamics of infected wound healing in rats. A: Nanostructured carbonized sorbents were

Multiple data obtained on rats with different levels of bacterial contamination suggest that NCSs may offer multiple specific advantages in topical wound management through their high adsorption ability in respect of both gram-positive and gram-negative bacteria as well as bacterial toxins. High adsorbing activity in respect of bacterial lipopolysaccharides has been measured by our group in a model studies. The other possible mechanism of beneficial action of the NCS, such as stimulation of tissue regeneration and binding of inflammation

Bioremediation is the use of microorganisms, their structures and their metabolic pathways to remove pollutants. Bioremediation is the most promising and cost effective technology widely used nowadays to clean up both soils and wastewaters containing organic or inorganic contaminants [9]. Discharge of pollutant-containing wastes has led to destruction of many agricultural lands and water bodies. Utilization of various microbes and their products to adsorb, transform and inactivate pollutants enhances the efficiency of the environment decontamination significantly. For bioremediation purposes, microbial cells (bacteria, fungi, algae, etc.) can be applied alone or in combination with some adsorbent, which can greatly enhance the viability and activity of the biological component. Such biocomposite sorbent, unlike mono-functional ion exchange resins, contains variety of functional sites including carboxyl, imidazole, sulphydryl, amino, phosphate, sulfate,

applied after injury. B: Wound healing in the control group.

thioether, phenol, carbonyl, amide and hydroxyl moieties.

mediators, are yet need to be studied.

**8.3. NCS in bioremediation** 

(**Figure 12**).

Problem of intractable wounds is one of persisting challenges in current clinical practice. In spite of modern antibiotics, hormonal and anti-inflammatory drugs, some chronic wounds and sores resist any treatment for weeks and months. The problem is especially serious in case of diabetic patients. The contributing factors are well-known and include high acidic wound environment, high concentration of bacteria (typically over 105 cells per gram tissue) and their toxins, continuous production of inflammatory cytokines, products of tissue necrosis and high osmotic pressure.

All chronic wounds are colonized by bacteria. The delayed closure for many chronic and acute wounds is associated with high levels of bacteria in the wounded tissues. Even at lower levels bacteria hinder wound healing due to toxin secretion either directly from viable cells (exotoxins) or as a result of cell lysis (endotoxins). These toxins tend to cause local necrosis and disrupt the delicate balance of critical mediators such as cytokines and proteases necessary for healing progression. The swelling of the surrounding tissues (edema) often causes disturbances in oxygen delivery, which in turn leads to gangrenous and secondary necrotic processes. Therefore, control and removal of toxins and bacteria should be considered as key elements of a successful wound-healing therapy.

Taking these circumstances into account, it becomes obvious that chemical (pharmacological) treatment alone is rather inefficient in treatment of such wounds. A common topical agent used to combat bacterial burden in chronic wounds is disperse silver [52]. Recent comparative evaluation of various therapeutic methods has shown that the application of carbonized adsorbing materials to the necrosis zones is even more efficient: it lowers intoxication, stabilizes the blood level of glucose, improves indices of immunological reactivity, promotes a more dynamic course of a wound process, and reduces the time of treatment [53]. Some possible factors contributing to the efficiency of the NCS in wound healing are presented in **Figure 11**.

**Figure 11.** Hypothetical mechanisms of beneficial effects of NCS in wound healing processes: 1) stimulation of tissue regeneration; 2) binding of microorganisms and their toxins; 3) adsorption of inflammation factors and products of necrosis; 4) direct antimicrobial action; 5) capillary drainage.

Our studies have demonstrated that the use of NCS indeed can develop into an outstanding method for stimulation of wound healing. We produced in rats infected injuries, which healing typically occurs in 10-12 days. In the case the NCS were applied directly after the injury, an improvement and acceleration in wound healing was systematically observed (**Figure 12**).

**Figure 12.** Dynamics of infected wound healing in rats. A: Nanostructured carbonized sorbents were applied after injury. B: Wound healing in the control group.

Multiple data obtained on rats with different levels of bacterial contamination suggest that NCSs may offer multiple specific advantages in topical wound management through their high adsorption ability in respect of both gram-positive and gram-negative bacteria as well as bacterial toxins. High adsorbing activity in respect of bacterial lipopolysaccharides has been measured by our group in a model studies. The other possible mechanism of beneficial action of the NCS, such as stimulation of tissue regeneration and binding of inflammation mediators, are yet need to be studied.

## **8.3. NCS in bioremediation**

288 Composites and Their Applications

tissue necrosis and high osmotic pressure.

healing are presented in **Figure 11**.

**sores** 

**8.2. Nanostructured carbonized materials for treatment of chronic wounds and** 

Problem of intractable wounds is one of persisting challenges in current clinical practice. In spite of modern antibiotics, hormonal and anti-inflammatory drugs, some chronic wounds and sores resist any treatment for weeks and months. The problem is especially serious in case of diabetic patients. The contributing factors are well-known and include high acidic wound environment, high concentration of bacteria (typically over 105 cells per gram tissue) and their toxins, continuous production of inflammatory cytokines, products of

All chronic wounds are colonized by bacteria. The delayed closure for many chronic and acute wounds is associated with high levels of bacteria in the wounded tissues. Even at lower levels bacteria hinder wound healing due to toxin secretion either directly from viable cells (exotoxins) or as a result of cell lysis (endotoxins). These toxins tend to cause local necrosis and disrupt the delicate balance of critical mediators such as cytokines and proteases necessary for healing progression. The swelling of the surrounding tissues (edema) often causes disturbances in oxygen delivery, which in turn leads to gangrenous and secondary necrotic processes. Therefore, control and removal of toxins and bacteria

Taking these circumstances into account, it becomes obvious that chemical (pharmacological) treatment alone is rather inefficient in treatment of such wounds. A common topical agent used to combat bacterial burden in chronic wounds is disperse silver [52]. Recent comparative evaluation of various therapeutic methods has shown that the application of carbonized adsorbing materials to the necrosis zones is even more efficient: it lowers intoxication, stabilizes the blood level of glucose, improves indices of immunological reactivity, promotes a more dynamic course of a wound process, and reduces the time of treatment [53]. Some possible factors contributing to the efficiency of the NCS in wound

**Figure 11.** Hypothetical mechanisms of beneficial effects of NCS in wound healing processes: 1) stimulation of tissue regeneration; 2) binding of microorganisms and their toxins; 3) adsorption of inflammation factors and products of necrosis; 4) direct antimicrobial action; 5) capillary drainage.

should be considered as key elements of a successful wound-healing therapy.

Bioremediation is the use of microorganisms, their structures and their metabolic pathways to remove pollutants. Bioremediation is the most promising and cost effective technology widely used nowadays to clean up both soils and wastewaters containing organic or inorganic contaminants [9]. Discharge of pollutant-containing wastes has led to destruction of many agricultural lands and water bodies. Utilization of various microbes and their products to adsorb, transform and inactivate pollutants enhances the efficiency of the environment decontamination significantly. For bioremediation purposes, microbial cells (bacteria, fungi, algae, etc.) can be applied alone or in combination with some adsorbent, which can greatly enhance the viability and activity of the biological component. Such biocomposite sorbent, unlike mono-functional ion exchange resins, contains variety of functional sites including carboxyl, imidazole, sulphydryl, amino, phosphate, sulfate, thioether, phenol, carbonyl, amide and hydroxyl moieties.

Compared to "classical" sorbents, the bio-sorbents are cheaper, more effective alternatives for the removal of metallic elements, especially heavy metals from aqueous solution. Therefore, the bio-composite sorbents are increasingly widely used for heavy pollutants removal. This is now a field of intensive investigations focusing on microbial cellular structure, biosorption performance, material pretreatment, modification, regeneration/reuse, modeling of biosorption (isotherm and kinetic models), the development of novel biosorbents, their evaluation, potential application and future. A potent supportive discipline in bioremediation studies is molecular biotechnology, capable to elucidate the mechanisms at molecular level and to construct engineered organisms with higher biosorption capacity and selectivity.

Heterogeneous Composites on the Basis of Microbial Cells and Nanostructured Carbonized Sorbents 291

Summarizing, we would like to emphasize that further studies and better understanding of the interactions between CNS and microbial cells are necessary. The future use of living cells as biocatalysts, especially in the environmental field, needs more systematic investigations of the microbial adsorption phenomenon. For this purpose it is necessary to develop and expand interdisciplinary collaboration networks connecting biologists, chemists, physicists

This newly gained interdisciplinary knowledge could significantly stimulate development of novel immobilized bio-catalysts possessing high activity, selectivity and stability. Taking into account the wide spectrum of abilities of microorganisms and carbonized surfaces carriers, this ambitious mission does not look like an impossible one. Undoubtedly, in the coming years we will see the expanding of the application spheres of CNS-based

Zulkhair Mansurov, Makhmut Biisenbaev, Irina Savitskaya, Aida Kistaubaeva, Nuraly

The authors thank Prof. Dr. Gerhard Artmann and Prof. Dr. Dr. Aysegül Temiz Artmann (Institute of Bioengineering, Aachen University of Applied Sciences) for their all-round

[1] Zobell, C.E., *The Effect of Solid Surfaces upon Bacterial Activity.* J Bacteriol, 1943. 46(1): p.

[2] John, D.E. and J.B. Rose, *Review of factors affecting microbial survival in groundwater.*

[4] Stoodley, P., et al., *Biofilms as complex differentiated communities.* Annu Rev Microbiol,

[5] Kannan, A.M., et al., *Bio-batteries and bio-fuel cells: leveraging on electronic charge transfer* 

[6] Shibasaki, S., H. Maeda, and M. Ueda, *Molecular display technology using yeast--arming* 

[7] Willner, I., B. Willner, and E. Katz, *Biomolecule-nanoparticle hybrid systems for bioelectronic* 

[3] Costerton, J.W., et al., *Microbial biofilms.* Annu Rev Microbiol, 1995. 49: p. 711-45.

*Al-Farabi Kazakh National University, Microbiology Department, Almaty, Kazakhstan* 

*Aachen University of Applied Sciences, Institute of Bioengineering, Jülich, Germany* 

and biochemical engineers.

**Author details** 

**Acknowledgement** 

**9. References** 

39-56.

2002. 56: p. 187-209.

Ilya Digel

heterogeneous composite biomaterials.

Akimbekov and Azhar Zhubanova

support in performing these studies.

Environ Sci Technol, 2005. 39(19): p. 7345-56.

*technology.* Anal Sci, 2009. 25(1): p. 41-9.

*proteins.* J Nanosci Nanotechnol, 2009. 9(3): p. 1665-78.

*applications.* Bioelectrochemistry, 2007. 70(1): p. 2-11.

**Figure 13.** Electron microphotograph of the heterogeneous bio-composite bioremediation material created on the basis of NCS and bacterial cells Pseudomonas aeruginosa.

Due to their remarkable properties, nanostructured carbon materials such as carbonized grape stones and rice husk can be used as sorbents for extraction of toxic and radioactive elements. Current joint research conducted at the al-Farabi Kazakh National University (Microbiology Dept. of the Biology Faculty together with the Institute of Combustion problems) is aimed to create cost-effective and sustainable bio-composite materials on the basis of microbial cells adsorbed NCS of plant origin. Electron microscopy observations confirmed that multiple bioremediation-valuable cells can successfully attach, survive and proliferate inside the porous network of the NCS (**Figure 13**). The resulting heterogeneous biological composite materials possess outstanding pollutant-binding and transforming properties accompanied by high specificity, depending on the particular microbial strain used. In our model experiments, the obtained materials specifically adsorbed up to 95% metals from solutions. For cleaning of oil-polluted soils, we are currently developing a heterogeneous composite on the basis of carbonized sorbent and an immobilized microbial consortium consisting of bacterial strains with high oil-oxidizing activity. First encouraging results were obtained in the field experiments on oil-polluted soils.

Summarizing, we would like to emphasize that further studies and better understanding of the interactions between CNS and microbial cells are necessary. The future use of living cells as biocatalysts, especially in the environmental field, needs more systematic investigations of the microbial adsorption phenomenon. For this purpose it is necessary to develop and expand interdisciplinary collaboration networks connecting biologists, chemists, physicists and biochemical engineers.

This newly gained interdisciplinary knowledge could significantly stimulate development of novel immobilized bio-catalysts possessing high activity, selectivity and stability. Taking into account the wide spectrum of abilities of microorganisms and carbonized surfaces carriers, this ambitious mission does not look like an impossible one. Undoubtedly, in the coming years we will see the expanding of the application spheres of CNS-based heterogeneous composite biomaterials.

## **Author details**

Zulkhair Mansurov, Makhmut Biisenbaev, Irina Savitskaya, Aida Kistaubaeva, Nuraly Akimbekov and Azhar Zhubanova *Al-Farabi Kazakh National University, Microbiology Department, Almaty, Kazakhstan* 

Ilya Digel

290 Composites and Their Applications

and selectivity.

Compared to "classical" sorbents, the bio-sorbents are cheaper, more effective alternatives for the removal of metallic elements, especially heavy metals from aqueous solution. Therefore, the bio-composite sorbents are increasingly widely used for heavy pollutants removal. This is now a field of intensive investigations focusing on microbial cellular structure, biosorption performance, material pretreatment, modification, regeneration/reuse, modeling of biosorption (isotherm and kinetic models), the development of novel biosorbents, their evaluation, potential application and future. A potent supportive discipline in bioremediation studies is molecular biotechnology, capable to elucidate the mechanisms at molecular level and to construct engineered organisms with higher biosorption capacity

**Figure 13.** Electron microphotograph of the heterogeneous bio-composite bioremediation material

Due to their remarkable properties, nanostructured carbon materials such as carbonized grape stones and rice husk can be used as sorbents for extraction of toxic and radioactive elements. Current joint research conducted at the al-Farabi Kazakh National University (Microbiology Dept. of the Biology Faculty together with the Institute of Combustion problems) is aimed to create cost-effective and sustainable bio-composite materials on the basis of microbial cells adsorbed NCS of plant origin. Electron microscopy observations confirmed that multiple bioremediation-valuable cells can successfully attach, survive and proliferate inside the porous network of the NCS (**Figure 13**). The resulting heterogeneous biological composite materials possess outstanding pollutant-binding and transforming properties accompanied by high specificity, depending on the particular microbial strain used. In our model experiments, the obtained materials specifically adsorbed up to 95% metals from solutions. For cleaning of oil-polluted soils, we are currently developing a heterogeneous composite on the basis of carbonized sorbent and an immobilized microbial consortium consisting of bacterial strains with high oil-oxidizing activity. First encouraging

created on the basis of NCS and bacterial cells Pseudomonas aeruginosa.

results were obtained in the field experiments on oil-polluted soils.

*Aachen University of Applied Sciences, Institute of Bioengineering, Jülich, Germany* 

## **Acknowledgement**

The authors thank Prof. Dr. Gerhard Artmann and Prof. Dr. Dr. Aysegül Temiz Artmann (Institute of Bioengineering, Aachen University of Applied Sciences) for their all-round support in performing these studies.

## **9. References**


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**Chapter 12** 

© 2012 Ranđelović et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

© 2012 Ranđelović et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**New Composite Materials in** 

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/48390

**1. Introduction** 

**the Technology for Drinking Water** 

**Purification from Ionic and Colloidal Pollutants** 

Marjan S. Ranđelović, Aleksandra R. Zarubica and Milovan M. Purenović

Composite materials (composites) are inherently heterogeneous and represent a defined combination of chemically and structurally different constituent materials, ensuring the required properties such as mechanical strength, stiffness, low density, or other specific characteristics depending on their purpose. Therefore, composite material is a system composed of two or more physically distinct phases whose combination produces a synergistic effect and aggregate properties that are different from those of its constituents. Favorable characteristics of composite materials were known to the people even in the period BC (before Christ-Century) and were used in order to improve the quality of human daily life. For example, it is known that in the ancient period, people made bricks that were reinforced with straw, and thus secured greater longevity and durability of their buildings. The incorporation of the straw improves the strength, toughness and thermal insulation properties of these composites. In principle, the degree of reinforcement (volume fraction of straw) and the level of alignment of the straw stalks (and their lengths) may be adjusted so that not only the properties but their anisotropy may be optimised differently in various parts of the structure [1]. Significant development and application of composites began in the second half of the 20th century, wherein their diversity and areas of application are constantly increasing. Development of composite materials is resulted mainly from the increasing need for materials with better mechanical characteristics that would be used as components in various constructions. For this purpose, such composites should have an adequate strength, stiffness, good oxidation resistance and low weight. Intensive study of composite materials and their processing methods has caused that these materials replace metals and alloys and become indispensable in the manufacture of parts for automobiles, spacecrafts, sports equipment etc. In terms of exploiting modern engineering composites


## **New Composite Materials in the Technology for Drinking Water Purification from Ionic and Colloidal Pollutants**

Marjan S. Ranđelović, Aleksandra R. Zarubica and Milovan M. Purenović

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/48390

## **1. Introduction**

294 Composites and Their Applications

51(1): p. 64-73.

19(15): p. S32-6.

CRC Press. xiii, 312 p.

Scand, 2006. 64(5): p. 314-8.

1997, London: Taylor & Francis.

783-6.

[45] Guarner, F., et al., *Should yoghurt cultures be considered probiotic?* Br J Nutr, 2005. 93(6): p.

[46] Montalto, M., et al., *Probiotic treatment increases salivary counts of lactobacilli: a double-*

[47] Caglar, E., et al., *Salivary mutans streptococci and lactobacilli levels after ingestion of the probiotic bacterium Lactobacillus reuteri ATCC 55730 by straws or tablets.* Acta Odontol

[48] Sadykov, R., et al., *Oral lead exposure induces dysbacteriosis in rats.* J Occup Health, 2009.

[49] Gershwin, M.E. and A. Belay, *Spirulina in human nutrition and health*. 2008, Boca Raton:

[50] Deng, R. and T.J. Chow, *Hypolipidemic, antioxidant, and antiinflammatory activities of* 

[51] Vonshak, A., *Spirulina platensis (arthrospira) : physiology, cell-biology and biotechnology*.

[52] Elliott, C., *The effects of silver dressings on chronic and burns wound healing.* Br J Nurs, 2010.

[53] Kuliev, R.A. and R.F. Babaev, [Physical factors in the comprehensive therapy of purulent wounds in diabetes mellitus]. Probl Endokrinol (Mosk), 1991. 37(5): p. 24-6.

*blind, randomized, controlled study.* Digestion, 2004. 69(1): p. 53-6.

*microalgae Spirulina.* Cardiovasc Ther, 2010. 28(4): p. e33-45.

Composite materials (composites) are inherently heterogeneous and represent a defined combination of chemically and structurally different constituent materials, ensuring the required properties such as mechanical strength, stiffness, low density, or other specific characteristics depending on their purpose. Therefore, composite material is a system composed of two or more physically distinct phases whose combination produces a synergistic effect and aggregate properties that are different from those of its constituents. Favorable characteristics of composite materials were known to the people even in the period BC (before Christ-Century) and were used in order to improve the quality of human daily life. For example, it is known that in the ancient period, people made bricks that were reinforced with straw, and thus secured greater longevity and durability of their buildings. The incorporation of the straw improves the strength, toughness and thermal insulation properties of these composites. In principle, the degree of reinforcement (volume fraction of straw) and the level of alignment of the straw stalks (and their lengths) may be adjusted so that not only the properties but their anisotropy may be optimised differently in various parts of the structure [1]. Significant development and application of composites began in the second half of the 20th century, wherein their diversity and areas of application are constantly increasing. Development of composite materials is resulted mainly from the increasing need for materials with better mechanical characteristics that would be used as components in various constructions. For this purpose, such composites should have an adequate strength, stiffness, good oxidation resistance and low weight. Intensive study of composite materials and their processing methods has caused that these materials replace metals and alloys and become indispensable in the manufacture of parts for automobiles, spacecrafts, sports equipment etc. In terms of exploiting modern engineering composites

© 2012 Ranđelović et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Ranđelović et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

this remains a central principle. Modern composites can be said to have "designed microand nanostructures" which means that the constituents of composites have much more finely divided structures and tend to have sizes in the micrometre or nanometre range. Basic factors affecting properties of composites are as follows:

New Composite Materials in the Technology

for Drinking Water Purification from Ionic and Colloidal Pollutants 297

composition determine the most dominant features of the composite as a unit. However, it should be noted here that the composite does not possess properties of a single component but exhibits qualitatively new features, because of which it is considered as a new material. In addition to the dominant use of composites as structural elements, important application of composite materials is in the water purification technologies. In this field of application, composites usually have the role of adsorbent, electrochemically active materials, catalysts, photocatalysts etc. Bearing in mind that the material efficiency in the removal of harmful substances from water is higher if greater is its surface area, there are tends of scientists to develop these materials with required and defined nanostructures. In addition to the specific surface area increasing, nanostructured materials exhibit a qualitatively new properties compared to the related structure at the micro or macro scale. In this manner, it is developed specific procedure for certain metal hydroxides and natural organic matter layering onto alumosilicate matrix as well as procedures of microalloying which both lead to significant changes of the surface acido-basic and electrical properties of the alumosilicate matrix. The nano-scale composites provide an opportunity to study the phase boundaries and phenomena occurring at the surface, interface boundaries and within intergranular area

during composites synthesis or during their interaction with aqueous solutions.

relatively isolated and not well discussed.

**and coating/layering in the composite synthesis** 

[7].

**2. An overview and trends in use of composites in industrial plants** 

Nanocomposites based on polymers represent an area of significant scientific interest and developing industrial practice. Despite the proven benefits of polymer based nanocomposites in the scope of their mechanical properties, and some distinctive combination/synergism of improved structural features, the real application remains still

An insight in the historical (re)view on polymer nano-composites showed on the first type used based on the combination of natural fillers and polymers in the 90s [3-6] up to estimated 145 million USD spent at huge market of polymer based nano-composites in 2013

**3. The concepts of interphase boundaries modification, microalloying** 

Methods and techniques for managing properties of composite materials include the selection and modification of constituent materials as well as changing the interface boundaries within the composite. Some composites are most commonly fabricated by impregnation (infiltration) of the matrix or matrix precursor in the liquid state into the appropriate filler preform. The connection between the constituents depends on the microstructure and chemistry of the interface boundary. The matrix and filler are connected by chemical bonds, interdiffusion, van der Waals forces and mechanical interlocking [2]. The first three interactions require very close filler-matrix contact that can be achieved if the matrix or matrix precursor wetting the surface of filler during the infiltration of matrix or matrix precursors in the filler preform. Effective wetting means that the liquid is evenly


Good bonding (adhesion) between matrix and dispersed phase provides a high level of mechanical properties of the composite via the interface. In addition, interfaces are responsible for numerous processes of electron transfers and play crucial role in redox processes, heterogeneous catalysis, adsorption etc. Usually, there are three forms of interface between the two phases within the composite:


Current challenges in the field of composite materials are associated with the extension of their application area from structural composites to functional and multifunctional composites. In this respect, a great improvement of composite materials through processing has been made enabling the development of composite materials for electrical, thermal and other functional applications that are relevant to current technological needs. Examples of functions are joining, repair, sensing, actuation, deicing (as needed for aircraft and bridges), energy conversion (as needed to generate clean energy), electrochemical electrodes, electrical connection, thermal contact improvement and heat dissipation (*i.e.*, cooling, as needed for microelectronics and aircrafts) [2]. Modern processing includes the use of additives (which may be introduced as liquids or solids), the combined use of fillers at the micrometer and nanometer scales, the formation of hybrids, the modification of the interfaces in a composite and control over the microstructure. Therefore, it can be said that the development of composite materials for current technological needs must be application driven and process oriented. The conventional composites engineering approach, which is focused on mechanics and purely structural applications, is in contrast to mentioned modern practice.

On the contemporary level of science development it is known that materials of certain characteristics can be obtained only by strictly defined procedures of processing and depend on their chemical composition and structure. Since composites are heterogeneous systems, as already has been noted, the matrix is of great importance whose structure and chemical composition determine the most dominant features of the composite as a unit. However, it should be noted here that the composite does not possess properties of a single component but exhibits qualitatively new features, because of which it is considered as a new material. In addition to the dominant use of composites as structural elements, important application of composite materials is in the water purification technologies. In this field of application, composites usually have the role of adsorbent, electrochemically active materials, catalysts, photocatalysts etc. Bearing in mind that the material efficiency in the removal of harmful substances from water is higher if greater is its surface area, there are tends of scientists to develop these materials with required and defined nanostructures. In addition to the specific surface area increasing, nanostructured materials exhibit a qualitatively new properties compared to the related structure at the micro or macro scale. In this manner, it is developed specific procedure for certain metal hydroxides and natural organic matter layering onto alumosilicate matrix as well as procedures of microalloying which both lead to significant changes of the surface acido-basic and electrical properties of the alumosilicate matrix. The nano-scale composites provide an opportunity to study the phase boundaries and phenomena occurring at the surface, interface boundaries and within intergranular area during composites synthesis or during their interaction with aqueous solutions.

296 Composites and Their Applications

 Properties of phases; Amount of phases;

reinforcement;

constituents;

modern practice.

factors affecting properties of composites are as follows:

Bonding and the interface between the phases;

between the two phases within the composite:

this remains a central principle. Modern composites can be said to have "designed microand nanostructures" which means that the constituents of composites have much more finely divided structures and tend to have sizes in the micrometre or nanometre range. Basic

Size, distribution and shape (particles, flakes, fibers, laminates) of the dispersed phase -

Good bonding (adhesion) between matrix and dispersed phase provides a high level of mechanical properties of the composite via the interface. In addition, interfaces are responsible for numerous processes of electron transfers and play crucial role in redox processes, heterogeneous catalysis, adsorption etc. Usually, there are three forms of interface

1. Direct bonding with no intermediate layer. In this case adhesion ("wetting") is

2. Intermediate layer in form of solid solution of the matrix and dispersed phases

Current challenges in the field of composite materials are associated with the extension of their application area from structural composites to functional and multifunctional composites. In this respect, a great improvement of composite materials through processing has been made enabling the development of composite materials for electrical, thermal and other functional applications that are relevant to current technological needs. Examples of functions are joining, repair, sensing, actuation, deicing (as needed for aircraft and bridges), energy conversion (as needed to generate clean energy), electrochemical electrodes, electrical connection, thermal contact improvement and heat dissipation (*i.e.*, cooling, as needed for microelectronics and aircrafts) [2]. Modern processing includes the use of additives (which may be introduced as liquids or solids), the combined use of fillers at the micrometer and nanometer scales, the formation of hybrids, the modification of the interfaces in a composite and control over the microstructure. Therefore, it can be said that the development of composite materials for current technological needs must be application driven and process oriented. The conventional composites engineering approach, which is focused on mechanics and purely structural applications, is in contrast to mentioned

On the contemporary level of science development it is known that materials of certain characteristics can be obtained only by strictly defined procedures of processing and depend on their chemical composition and structure. Since composites are heterogeneous systems, as already has been noted, the matrix is of great importance whose structure and chemical

Orientation of the dispersed phase - reinforcement (random or preferred).

provided by either covalent bonding or van der Waals force;

3. Intermediate layer (interphase) in form of a third bonding phase (adhesive).

## **2. An overview and trends in use of composites in industrial plants**

Nanocomposites based on polymers represent an area of significant scientific interest and developing industrial practice. Despite the proven benefits of polymer based nanocomposites in the scope of their mechanical properties, and some distinctive combination/synergism of improved structural features, the real application remains still relatively isolated and not well discussed.

An insight in the historical (re)view on polymer nano-composites showed on the first type used based on the combination of natural fillers and polymers in the 90s [3-6] up to estimated 145 million USD spent at huge market of polymer based nano-composites in 2013 [7].

## **3. The concepts of interphase boundaries modification, microalloying and coating/layering in the composite synthesis**

Methods and techniques for managing properties of composite materials include the selection and modification of constituent materials as well as changing the interface boundaries within the composite. Some composites are most commonly fabricated by impregnation (infiltration) of the matrix or matrix precursor in the liquid state into the appropriate filler preform. The connection between the constituents depends on the microstructure and chemistry of the interface boundary. The matrix and filler are connected by chemical bonds, interdiffusion, van der Waals forces and mechanical interlocking [2]. The first three interactions require very close filler-matrix contact that can be achieved if the matrix or matrix precursor wetting the surface of filler during the infiltration of matrix or matrix precursors in the filler preform. Effective wetting means that the liquid is evenly distributed over the surface of filler, while a poor wetting means that the liquid drops formed on the surface. Wettability can be increased by applying the coatings, adding wetting agents or by chemical surface functionalization (the introduction of functional groups on the surface that increase wettability) thereby changing the surface energy. If the filler is carbon fiber, surface treatments involve oxidation treatments and the use of coupling agents, wetting agents, and/or coatings. Often, metals or ceramics are used as coatings for carbon fillers. Metallic coatings are usually formed by coating carbon fiber reinforcements with metals *i.e.* Ni, Cu and Ag. Examples of ceramic coatings are TiC, SiC, B4C, TiB2, TiN which are distributed by using Chemical Vapor Deposition (CVD) technique or by solution coating methods starting from organometalic compounds. Therefore, these are examples of application of coatings on carbon materials to illustrate the method of modification of surface properties.

In the case of metal-ceramic composites, certain liquid metals react with ceramic preform during infiltration. For instances, composites based on the Al–Al2O3 system can be obtained by Reactive Metal Penetration (RMP) method which is based on infiltration of ceramic preforms by a liquid metal, generally aluminium or aluminium alloys [8,9]. During the process, a liquid metal simultaneously reacts and penetrates the ceramic preform, usually silica or a silicate, resulting in a metal-ceramic composite characterized by two phases that are interpenetrated. Another example is the reaction between SiC and Al during the infiltration of molten aluminum in a preheated preform:

$$4\text{Al} + 3\text{SiC} \rightarrow \text{Al} \text{Cl} \rightarrow 3\text{Si} \tag{1}$$

New Composite Materials in the Technology

for Drinking Water Purification from Ionic and Colloidal Pollutants 299

conductivity, and dielectric properties of matrix. Microalloying, as a known modern procedure for changing the intrinsic semiconductor properties, by authors' original works (Purenovic et al.), get more and more important role in the control of some structurally sensitive properties of metals, alloys, ceramics, composites and other materials. It is known that the nature of matter is determined by its composition and structure. There are many structurally sensitive properties of materials, but among the most sensitive are the conductivity, electrode potential, magnetic, catalytic and mechanical properties. Microalloying means adding certain elements in small (ppm) quantities, thereby modified structure results in a significant change in the value of conductivity and the electrode potential. Conducted own investigation and the results obtained showed an excellent rational electrochemical behavior of composites such as microalloyed aluminum, microalloyed magnesium, as well as composite ceramics and quartz sand microalloyed with aluminum and magnesium, in contact with aqueous solutions of electrolytes or water which contain harmful ingredients in ionic, molecular and colloidal state. Microalloyed and structurally modified composite ceramics have high porosity (30%), with the macro-, meso-, micro- and submicropores. There is direct relationship between porosity and structure of these composite materials, especially when it comes to nanostructured fragmented crystals. It is worth to emphasize the domination of amorphous phases with crystalline substructure, which is impossible to be removed, and it would be inappropriate to be removed, because the contact of crystals with amorphous layer is responsible for numerous processes of electrons exchange. By certain processes and reactions in the solid phase, the amorphous microalloyed aluminum, microalloyed amorphous magnesium, amorphous-crystalline structure of composite microalloyed ceramics and amorphous-crystalline structure of microalloyed quartz sand could be obtained. Many metals, alloys and composite electrode materials manifested significant differences in the reversible thermodynamic potential and

The manufacturing processes used to make composite ceramics can cause the development of liquid phases during sintering, and their retention as remnant glass at triple junctions and along grain boundaries and interphase boundaries after cooling to room temperature. Formed thin intergranular films are relevant to creep behavior at high temperatures, and also responsible for the strength of the bonding at interfaces. However, the heat treatment at elevated temperatures which is used for joining constituent materials and establishing the cohesive forces shows a disadvantage because cooling can lead to disturbance of established bonds between phases. Namely, during the cooling, differences in coefficients of thermal expansion could result in unequal contraction by which established bonds are broken. This problem is particularly evident in metal-ceramic composites, where high temperatures are

Processing of nanocomposites based on layered silicates is rather challenging activity to achieve the full technical and engineering potential, which is the field with the largest growth forecast [13-16]. The modification of silicates by use of organic components is

the steady corrosion potential.

usually applied during synthesis.

**4. Preparation of modern nano-composites** 

From the equation it can be seen that Si is generated during the reaction which is then dissolved in molten aluminum, while Al4C3 occurs at the SiC-Al interfacial boundary. The degree of reaction increases with increasing temperature. On the contrary, there are metals that in liquid state difficult wet the surface of the ceramic resulting in metal infiltration hindering. The difficulty of wetting and bonding of liquid metals to ceramic surfaces is related to atomic bonding in the ceramic lattice and can be improved by application of coatings. Coated particles (composite particles) are composed of solid phase covered with thinner or thicker layer of another material [10.11]. These coatings - layers on the surface are important for several reasons. In such way, the surface characteristics of the initial solid phase are modified and sintering conditions as well as molten metal infiltration can be better controlled.

As can be seen from examples, the processing of composite materials often involves high temperature and pressure to cause the joining of constituent materials forming a cohesive material. Generally, the matrix dictates the required temperature, pressure and processing time during composite synthesis. Sintering is an important factor in achieving the desired microstructure of ceramic based composites and includes very complex processes. In addition to surface coatings, an important influence on sintering has been exhibited by an addition of microalloying components, which significantly determine a microstructure and properties of ceramics [12]. The presence of small amounts of impurities in the starting material can vastly influence their mechanical, optical, electrical, color, diffusivity, electrical conductivity, and dielectric properties of matrix. Microalloying, as a known modern procedure for changing the intrinsic semiconductor properties, by authors' original works (Purenovic et al.), get more and more important role in the control of some structurally sensitive properties of metals, alloys, ceramics, composites and other materials. It is known that the nature of matter is determined by its composition and structure. There are many structurally sensitive properties of materials, but among the most sensitive are the conductivity, electrode potential, magnetic, catalytic and mechanical properties. Microalloying means adding certain elements in small (ppm) quantities, thereby modified structure results in a significant change in the value of conductivity and the electrode potential. Conducted own investigation and the results obtained showed an excellent rational electrochemical behavior of composites such as microalloyed aluminum, microalloyed magnesium, as well as composite ceramics and quartz sand microalloyed with aluminum and magnesium, in contact with aqueous solutions of electrolytes or water which contain harmful ingredients in ionic, molecular and colloidal state. Microalloyed and structurally modified composite ceramics have high porosity (30%), with the macro-, meso-, micro- and submicropores. There is direct relationship between porosity and structure of these composite materials, especially when it comes to nanostructured fragmented crystals. It is worth to emphasize the domination of amorphous phases with crystalline substructure, which is impossible to be removed, and it would be inappropriate to be removed, because the contact of crystals with amorphous layer is responsible for numerous processes of electrons exchange. By certain processes and reactions in the solid phase, the amorphous microalloyed aluminum, microalloyed amorphous magnesium, amorphous-crystalline structure of composite microalloyed ceramics and amorphous-crystalline structure of microalloyed quartz sand could be obtained. Many metals, alloys and composite electrode materials manifested significant differences in the reversible thermodynamic potential and the steady corrosion potential.

The manufacturing processes used to make composite ceramics can cause the development of liquid phases during sintering, and their retention as remnant glass at triple junctions and along grain boundaries and interphase boundaries after cooling to room temperature. Formed thin intergranular films are relevant to creep behavior at high temperatures, and also responsible for the strength of the bonding at interfaces. However, the heat treatment at elevated temperatures which is used for joining constituent materials and establishing the cohesive forces shows a disadvantage because cooling can lead to disturbance of established bonds between phases. Namely, during the cooling, differences in coefficients of thermal expansion could result in unequal contraction by which established bonds are broken. This problem is particularly evident in metal-ceramic composites, where high temperatures are usually applied during synthesis.

## **4. Preparation of modern nano-composites**

298 Composites and Their Applications

surface properties.

better controlled.

distributed over the surface of filler, while a poor wetting means that the liquid drops formed on the surface. Wettability can be increased by applying the coatings, adding wetting agents or by chemical surface functionalization (the introduction of functional groups on the surface that increase wettability) thereby changing the surface energy. If the filler is carbon fiber, surface treatments involve oxidation treatments and the use of coupling agents, wetting agents, and/or coatings. Often, metals or ceramics are used as coatings for carbon fillers. Metallic coatings are usually formed by coating carbon fiber reinforcements with metals *i.e.* Ni, Cu and Ag. Examples of ceramic coatings are TiC, SiC, B4C, TiB2, TiN which are distributed by using Chemical Vapor Deposition (CVD) technique or by solution coating methods starting from organometalic compounds. Therefore, these are examples of application of coatings on carbon materials to illustrate the method of modification of

In the case of metal-ceramic composites, certain liquid metals react with ceramic preform during infiltration. For instances, composites based on the Al–Al2O3 system can be obtained by Reactive Metal Penetration (RMP) method which is based on infiltration of ceramic preforms by a liquid metal, generally aluminium or aluminium alloys [8,9]. During the process, a liquid metal simultaneously reacts and penetrates the ceramic preform, usually silica or a silicate, resulting in a metal-ceramic composite characterized by two phases that are interpenetrated. Another example is the reaction between SiC and Al during the

From the equation it can be seen that Si is generated during the reaction which is then dissolved in molten aluminum, while Al4C3 occurs at the SiC-Al interfacial boundary. The degree of reaction increases with increasing temperature. On the contrary, there are metals that in liquid state difficult wet the surface of the ceramic resulting in metal infiltration hindering. The difficulty of wetting and bonding of liquid metals to ceramic surfaces is related to atomic bonding in the ceramic lattice and can be improved by application of coatings. Coated particles (composite particles) are composed of solid phase covered with thinner or thicker layer of another material [10.11]. These coatings - layers on the surface are important for several reasons. In such way, the surface characteristics of the initial solid phase are modified and sintering conditions as well as molten metal infiltration can be

As can be seen from examples, the processing of composite materials often involves high temperature and pressure to cause the joining of constituent materials forming a cohesive material. Generally, the matrix dictates the required temperature, pressure and processing time during composite synthesis. Sintering is an important factor in achieving the desired microstructure of ceramic based composites and includes very complex processes. In addition to surface coatings, an important influence on sintering has been exhibited by an addition of microalloying components, which significantly determine a microstructure and properties of ceramics [12]. The presence of small amounts of impurities in the starting material can vastly influence their mechanical, optical, electrical, color, diffusivity, electrical

4Al + 3SiC → Al4C3 + 3Si (1)

infiltration of molten aluminum in a preheated preform:

Processing of nanocomposites based on layered silicates is rather challenging activity to achieve the full technical and engineering potential, which is the field with the largest growth forecast [13-16]. The modification of silicates by use of organic components is needed to allow intercalation, and also in order to improve compatibility/nano-distribution some additional ingredients have to be applied. The thermal treatment as step in processing sequence helps proper stabilisation of nanocomposites that has to take into consideration the oxidative stability of the polymer substrate, the influence of the nano-filler and the impact of modifiers and compatibilisers.

New Composite Materials in the Technology

for Drinking Water Purification from Ionic and Colloidal Pollutants 301

vinylpyrrolidone) in the form of gradient copolymers are applied with unmodified montmorillonite for processing PP nano-composites. Such obtained nano-composites show partial exfoliation, the final visual appearance is similar to the classical ammonium modified systems, however better thermal and thermo-oxidative stability is proven [23]. The most important improvement is achieved in the mechanical vales comparing to the conventional

**6. Nanocomposites use in a competitive environment of the materials** 

be potential factors/elements of the interaction [24].

an affirmative effect in nano-composites for long-term stability.

Nanocomposites materials are very attractive from the scientific and practical point of view, although some other materials are also interesting, such as plastics, fillers, blends, and different additives fulfilling the specified product profile. In such competence, the lowest cost solution comprising acceptable material structure and properties/resistances would dominate. Even more, competitive (nano)composite materials would benefit from nanocomposites developments and keep their application fields with improved features. Most of nanocomposites materials applications are intended for long-term and outdoor use. This is important aspect on the need for relevant nanocomposites stability. Namely, it is known that inorganic fillers often show a negative effect on the oxidative stability to a varying extent. The interactions of the filler and the stabilizers over adsorption/desorption mechanisms are mainly responsible for the impact. The specific surface area of the filler and pore volumes, surface functionality, hydrophilicity, thermal and photo-sensation properties of the filler and transition metal content (ex. manganese, titanium, iron) have been found to

Polypropylene/montmorillonite nanocomposites, additionally stabilized with antioxidant, degrade much faster under photo-oxidative conditions than pure polypropylene [25,26].This phenomenon is attributed to active species/sites in the clay generated by photolysis or photo-oxidation, and by consequence interaction between antioxidant, montmorillonite and maleic anhydride modified polypropylene. In natural clay present iron may additionally play an active role in the dramatic modification of material oxidation conditions [27], and nanoparticles also catalyze the decomposition process [28]. The use of so-called filler deactivators or coupling agents is potential solution for diminishing the negative influence of fillers on the (photo)oxidative stability by blocking active sites on the filler surface. Amphiphilic modifiers with reactive chemical groups in the form of polymers, olygomers or low molecular weight molecules such as bisstearylamide or dodecenylsuccinic anhydride have been proposed [29].Thus, stabilizer systems containing filler deactivators should have

**7. Nano-composites materials for water treatments: State-of-the-art and** 

Clean drinking water is essential to human health, and also so-called technical water is a critical feedstock in a variety of key industries including electronics, pharmaceuticals and

polymer system.

**perspectives** 

Montmorillonite of natural origin is among the most used nano-fillers. Traditional nano-fillers contain metal ions and other contaminants that may influence the thermooxidative stability and features of the nanocomposites. Organic modification of the (natural/traditional) clay is usually realized by cation exchange with a long-chain amines or quaternary ammonium salts. Content of such involved organic material content within the clay may be up to 40 mas.%. Therefore, the total thermal resistance of the composite material highly depends on the thermal stability of the organic ingredient. The thermal stability of the ammonium salts is limited at the processing temperatures applied (ex. extrusion, injection molding, etc.). Namely, thermal degradation of ammonium salts starts at 180°C and may be even tentatively reduced by catalytically active sites on the alumosilicate layer [17].

The compatibiliser applied as organically modified filler is often polypropylene-g-maleic anhydride in amount from 5 to 25% in the final composite formulation. The inferior stability of such low molecular weight filler comparing to the parent polymer affects the total stability of the final polymer based nanocomposites.

## **5. An improvement of composites stability**

Nanocomposites may show higher stability due to increased barrier to oxygen, or lower stability because of undergone to hydrolysis through entrapped water [18,19]. In conventional practice stabilizer systems based on phenolic antioxidants and phosphites are applied, and in recent investigations new found components of filler degradation deactivators has been tested [20].

A traditional state-of-art polypropylene (PP) nanocomposite consisting of maleated PP and nano-clay is traditionally stabilized by a proven combination of phenolic antioxidant and phosphites. The polymer degradation may be completely prevented even after 5 extrusion cycles by using the patented stabilizer system AO-2 (based on oxazoline, oxazolone, oxirane, oxazine and isocyanate groups) [20], additionally improving mechanical properties of the resulting nano-composites and discoloration during processing and application.

The underlined thermal instability of the usual ammonium organic modifiers can be diminished by using the phosphonium, imidazolium, pyridinium, tropylium ions [21]. An alternative way to produce thermally stable nano-composites is the use of unmodified clays in combination with selected copolymers playing role of dispersants, intercalants, exfoliants and compatibilisers for PP nano-composites. In current processing of nano-composites different structures are identified such as polyethyleneoxide based nonionic surfactants [22] and amphiphilic copolymers based on long-chain acrylates [23]. Recently, more specifically poly(octadecylacrylate-co-maleic anhydride) and poly(octadecylacrylate-co-N-

vinylpyrrolidone) in the form of gradient copolymers are applied with unmodified montmorillonite for processing PP nano-composites. Such obtained nano-composites show partial exfoliation, the final visual appearance is similar to the classical ammonium modified systems, however better thermal and thermo-oxidative stability is proven [23]. The most important improvement is achieved in the mechanical vales comparing to the conventional polymer system.

300 Composites and Their Applications

impact of modifiers and compatibilisers.

by catalytically active sites on the alumosilicate layer [17].

stability of the final polymer based nanocomposites.

**5. An improvement of composites stability** 

deactivators has been tested [20].

needed to allow intercalation, and also in order to improve compatibility/nano-distribution some additional ingredients have to be applied. The thermal treatment as step in processing sequence helps proper stabilisation of nanocomposites that has to take into consideration the oxidative stability of the polymer substrate, the influence of the nano-filler and the

Montmorillonite of natural origin is among the most used nano-fillers. Traditional nano-fillers contain metal ions and other contaminants that may influence the thermooxidative stability and features of the nanocomposites. Organic modification of the (natural/traditional) clay is usually realized by cation exchange with a long-chain amines or quaternary ammonium salts. Content of such involved organic material content within the clay may be up to 40 mas.%. Therefore, the total thermal resistance of the composite material highly depends on the thermal stability of the organic ingredient. The thermal stability of the ammonium salts is limited at the processing temperatures applied (ex. extrusion, injection molding, etc.). Namely, thermal degradation of ammonium salts starts at 180°C and may be even tentatively reduced

The compatibiliser applied as organically modified filler is often polypropylene-g-maleic anhydride in amount from 5 to 25% in the final composite formulation. The inferior stability of such low molecular weight filler comparing to the parent polymer affects the total

Nanocomposites may show higher stability due to increased barrier to oxygen, or lower stability because of undergone to hydrolysis through entrapped water [18,19]. In conventional practice stabilizer systems based on phenolic antioxidants and phosphites are applied, and in recent investigations new found components of filler degradation

A traditional state-of-art polypropylene (PP) nanocomposite consisting of maleated PP and nano-clay is traditionally stabilized by a proven combination of phenolic antioxidant and phosphites. The polymer degradation may be completely prevented even after 5 extrusion cycles by using the patented stabilizer system AO-2 (based on oxazoline, oxazolone, oxirane, oxazine and isocyanate groups) [20], additionally improving mechanical properties of the

The underlined thermal instability of the usual ammonium organic modifiers can be diminished by using the phosphonium, imidazolium, pyridinium, tropylium ions [21]. An alternative way to produce thermally stable nano-composites is the use of unmodified clays in combination with selected copolymers playing role of dispersants, intercalants, exfoliants and compatibilisers for PP nano-composites. In current processing of nano-composites different structures are identified such as polyethyleneoxide based nonionic surfactants [22] and amphiphilic copolymers based on long-chain acrylates [23]. Recently, more specifically poly(octadecylacrylate-co-maleic anhydride) and poly(octadecylacrylate-co-N-

resulting nano-composites and discoloration during processing and application.

## **6. Nanocomposites use in a competitive environment of the materials**

Nanocomposites materials are very attractive from the scientific and practical point of view, although some other materials are also interesting, such as plastics, fillers, blends, and different additives fulfilling the specified product profile. In such competence, the lowest cost solution comprising acceptable material structure and properties/resistances would dominate. Even more, competitive (nano)composite materials would benefit from nanocomposites developments and keep their application fields with improved features. Most of nanocomposites materials applications are intended for long-term and outdoor use. This is important aspect on the need for relevant nanocomposites stability. Namely, it is known that inorganic fillers often show a negative effect on the oxidative stability to a varying extent. The interactions of the filler and the stabilizers over adsorption/desorption mechanisms are mainly responsible for the impact. The specific surface area of the filler and pore volumes, surface functionality, hydrophilicity, thermal and photo-sensation properties of the filler and transition metal content (ex. manganese, titanium, iron) have been found to be potential factors/elements of the interaction [24].

Polypropylene/montmorillonite nanocomposites, additionally stabilized with antioxidant, degrade much faster under photo-oxidative conditions than pure polypropylene [25,26].This phenomenon is attributed to active species/sites in the clay generated by photolysis or photo-oxidation, and by consequence interaction between antioxidant, montmorillonite and maleic anhydride modified polypropylene. In natural clay present iron may additionally play an active role in the dramatic modification of material oxidation conditions [27], and nanoparticles also catalyze the decomposition process [28]. The use of so-called filler deactivators or coupling agents is potential solution for diminishing the negative influence of fillers on the (photo)oxidative stability by blocking active sites on the filler surface. Amphiphilic modifiers with reactive chemical groups in the form of polymers, olygomers or low molecular weight molecules such as bisstearylamide or dodecenylsuccinic anhydride have been proposed [29].Thus, stabilizer systems containing filler deactivators should have an affirmative effect in nano-composites for long-term stability.

## **7. Nano-composites materials for water treatments: State-of-the-art and perspectives**

Clean drinking water is essential to human health, and also so-called technical water is a critical feedstock in a variety of key industries including electronics, pharmaceuticals and

food processing industries. Taking into consideration that available supplies of fresh water are limited (due to population growth, extended deficiency, stringent health regulations, and competing demands from a variety of users/consumers) the world is facing with challenges to satisfy demands on high water quality standards and quantities (volumes). Benefits and trends in nano-scale science, chemistry and engineering impose that many of the current problems regarding green chemistry may be resolved using nano-sorbents, nano-catalysts, nanoparticles and nanostructured catalytic membranes. Nano-materials are characterized by a number of key physicochemical properties being particularly attractive for water purification treatments. Nanomaterials have much large specific surface area than bulk respect particles (mass to volume ratio), also they can be functionalized with reactive chemical groups specific in affinity to a given model compound. These materials may possess redox features and take part in shape- and structural-dependent catalyzed reactions of water purification. In aqueous solutions, they can serve as sorbents/catalysts for toxic metal ions, radionuclides, organic and inorganic solutes/anions [30]. Moreover, nano-materials can be used in selective targeting of biochemically constituents of aquatic bacteria and viruses. The nano-materials seems to be key components in future environmental friendly and cost-effective functional materials to desalinate public and polluted waters world-wide, for purification of water contaminated by pesticides, pharmaceuticals, phenol and other aromatics. The presence of heavy metals in water exhibits a variety of harmful effects on the living organisms in polluted ecosystems. The removal of heavy metals from water includes the following procedures: chemical precipitation, coagulation/flocculation, membrane processes, ion exchange, adsorption, electrochemical precipitation, etc. [31,32]. However, the application of composite materials in the controlling of pollutants in the environment and drinking water is significant [33,34], as described in further text.

New Composite Materials in the Technology

for Drinking Water Purification from Ionic and Colloidal Pollutants 303

species and polyelectrolytes molecules over hydrogen bonding (amino/amidic groups of the polyelectrolyte, and the –OH and –H groups of Al species are involved) and electrostatic forces/interactions. This resulted in new composite material. The main advantage of composite coagulants is lower residual aluminium concentration that remains in the treated sample, and more efficient treatments of waters (organic matter removal) can be realized [36]. Additional benefit is in cost effective process in the absence of specific equipment for handling the polyelectrolyte (ex. pumping system, etc.). Taking into account faster flocculation, increased efficiency and cost effectiveness, such new

Porous ceramic composites can be prepared by silver nanoparticles-decoration using a silver nanoparticle colloidal solution and an aminosilane coupling agent [37]. The interaction between the nanoparticles and the ceramics comprises the coordination bonds between the –NH2 group and the silver atoms on the surface of the nanoparticles. The composite can be stored for long periods without losing of nanoparticles, also being highly resistance to ultrasonic irradiation and washing. Such composite has shown high sterilization property as an antibacterial water filter [37]. This low cost composite, bearing in mind commonly available synthesis, simple preparation, the use of cheap and non-toxic reagents in the procedure, may be imposed as a potential solution for widespread use in

Ultrafine AgO particles-decorated porous ceramic composites are prepared based on the main ingredient, cristoballite. The results on composite structure show that silver(II)oxide decorated diatomite-based porous ceramic composites possess crystal structure, and are composed of tetragonal cristoballite, monoclinic silver(II)oxide and cubic silver(I)oxide [38]. Such AgO-decorated porous ceramic composites show a strong antimicrobial activity and an algal-inhibition capacity. As the extension time is longer, the antibacterial effects are

Actual nanostructured composite materials based on multi-walled carbon nanotubes (MWCNT) and titania exhibited strong interphase structure between MWCNT and titania. This contact and interaction facilitated a homogeneous deposition/coverage of titania over MWCNT [39]. The photo-catalytic activity of the prepared composite materials was tested in the conversion of phenol from model watery solution under UV or visible light. The results showed higher photo-catalytic activity of the composite MWCNT and titania than over mechanical mixture proving an assumption on the existence of the interphase structure

Nanocomposite membranes based on silica/titania nanotubes over porous alumina supports membranes were prepared [40]. An inserting of amorphous silica into nanophase titania caused the surpressed of phase transformation from anatase to rutile, and decreased the titania particle size. Good photo-catalytic activity of organic contaminants degradation, and wettability of composite membrane under UV-irradiation, helped to obtain high permeate

composite material seems to be promising one.

water treatments.

enhanced up to 99.9% [38].

flux across the composite membrane [40].

effect [39].

The use of zeolites, natural or synthetic ones in waste water treatments is highly limited due to low adsorption capacity in the case of former and relatively small grain size in latter. Modification of natural or synthetic zeolites toward composite material which would satisfy both essential properties is a challenging task. Tailoring synthetic zeolite resulted in a composite porous host supporting microcrystalline active phase of vermiculite matrix [35]. The vermiculite-based composite showed the same hydraulic properties as natural clinoptilolite with similar grain size (2-5 mm), while the rate of adsorption and maximal adsorption capacity was improved four times. In other words, cation exchange capacity is increased when compared to natural zeolite with a comparative grain size, ion-exchange kinetics are substantially improved in comparison to natural zeolite, and hydraulic conductivity is considerably higher that synthetic powdered zeolite [35].

The development of new composite material based on use of inorganic polymeric flocculants as a combination of anionic and cationic poly-aluminium chloride (PACl) in one unique polyelectrolyte is proposed [36]. The incorporation of the anionic polyelectrolyte into PACl structure noticeably affects its initial properties (*i.e.* turbidity, Al species distribution, pH and conductivity). Interactions are taking place between Al species and polyelectrolytes molecules over hydrogen bonding (amino/amidic groups of the polyelectrolyte, and the –OH and –H groups of Al species are involved) and electrostatic forces/interactions. This resulted in new composite material. The main advantage of composite coagulants is lower residual aluminium concentration that remains in the treated sample, and more efficient treatments of waters (organic matter removal) can be realized [36]. Additional benefit is in cost effective process in the absence of specific equipment for handling the polyelectrolyte (ex. pumping system, etc.). Taking into account faster flocculation, increased efficiency and cost effectiveness, such new composite material seems to be promising one.

302 Composites and Their Applications

water is significant [33,34], as described in further text.

powdered zeolite [35].

food processing industries. Taking into consideration that available supplies of fresh water are limited (due to population growth, extended deficiency, stringent health regulations, and competing demands from a variety of users/consumers) the world is facing with challenges to satisfy demands on high water quality standards and quantities (volumes). Benefits and trends in nano-scale science, chemistry and engineering impose that many of the current problems regarding green chemistry may be resolved using nano-sorbents, nano-catalysts, nanoparticles and nanostructured catalytic membranes. Nano-materials are characterized by a number of key physicochemical properties being particularly attractive for water purification treatments. Nanomaterials have much large specific surface area than bulk respect particles (mass to volume ratio), also they can be functionalized with reactive chemical groups specific in affinity to a given model compound. These materials may possess redox features and take part in shape- and structural-dependent catalyzed reactions of water purification. In aqueous solutions, they can serve as sorbents/catalysts for toxic metal ions, radionuclides, organic and inorganic solutes/anions [30]. Moreover, nano-materials can be used in selective targeting of biochemically constituents of aquatic bacteria and viruses. The nano-materials seems to be key components in future environmental friendly and cost-effective functional materials to desalinate public and polluted waters world-wide, for purification of water contaminated by pesticides, pharmaceuticals, phenol and other aromatics. The presence of heavy metals in water exhibits a variety of harmful effects on the living organisms in polluted ecosystems. The removal of heavy metals from water includes the following procedures: chemical precipitation, coagulation/flocculation, membrane processes, ion exchange, adsorption, electrochemical precipitation, etc. [31,32]. However, the application of composite materials in the controlling of pollutants in the environment and drinking

The use of zeolites, natural or synthetic ones in waste water treatments is highly limited due to low adsorption capacity in the case of former and relatively small grain size in latter. Modification of natural or synthetic zeolites toward composite material which would satisfy both essential properties is a challenging task. Tailoring synthetic zeolite resulted in a composite porous host supporting microcrystalline active phase of vermiculite matrix [35]. The vermiculite-based composite showed the same hydraulic properties as natural clinoptilolite with similar grain size (2-5 mm), while the rate of adsorption and maximal adsorption capacity was improved four times. In other words, cation exchange capacity is increased when compared to natural zeolite with a comparative grain size, ion-exchange kinetics are substantially improved in comparison to natural zeolite, and hydraulic conductivity is considerably higher that synthetic

The development of new composite material based on use of inorganic polymeric flocculants as a combination of anionic and cationic poly-aluminium chloride (PACl) in one unique polyelectrolyte is proposed [36]. The incorporation of the anionic polyelectrolyte into PACl structure noticeably affects its initial properties (*i.e.* turbidity, Al species distribution, pH and conductivity). Interactions are taking place between Al Porous ceramic composites can be prepared by silver nanoparticles-decoration using a silver nanoparticle colloidal solution and an aminosilane coupling agent [37]. The interaction between the nanoparticles and the ceramics comprises the coordination bonds between the –NH2 group and the silver atoms on the surface of the nanoparticles. The composite can be stored for long periods without losing of nanoparticles, also being highly resistance to ultrasonic irradiation and washing. Such composite has shown high sterilization property as an antibacterial water filter [37]. This low cost composite, bearing in mind commonly available synthesis, simple preparation, the use of cheap and non-toxic reagents in the procedure, may be imposed as a potential solution for widespread use in water treatments.

Ultrafine AgO particles-decorated porous ceramic composites are prepared based on the main ingredient, cristoballite. The results on composite structure show that silver(II)oxide decorated diatomite-based porous ceramic composites possess crystal structure, and are composed of tetragonal cristoballite, monoclinic silver(II)oxide and cubic silver(I)oxide [38]. Such AgO-decorated porous ceramic composites show a strong antimicrobial activity and an algal-inhibition capacity. As the extension time is longer, the antibacterial effects are enhanced up to 99.9% [38].

Actual nanostructured composite materials based on multi-walled carbon nanotubes (MWCNT) and titania exhibited strong interphase structure between MWCNT and titania. This contact and interaction facilitated a homogeneous deposition/coverage of titania over MWCNT [39]. The photo-catalytic activity of the prepared composite materials was tested in the conversion of phenol from model watery solution under UV or visible light. The results showed higher photo-catalytic activity of the composite MWCNT and titania than over mechanical mixture proving an assumption on the existence of the interphase structure effect [39].

Nanocomposite membranes based on silica/titania nanotubes over porous alumina supports membranes were prepared [40]. An inserting of amorphous silica into nanophase titania caused the surpressed of phase transformation from anatase to rutile, and decreased the titania particle size. Good photo-catalytic activity of organic contaminants degradation, and wettability of composite membrane under UV-irradiation, helped to obtain high permeate flux across the composite membrane [40].

## **8. New alumosilicate based composites chemically modified by coatings/thin layers – Tested in the removal of colloidal and ionic forms of harmful heavy metals from water**

New Composite Materials in the Technology

for Drinking Water Purification from Ionic and Colloidal Pollutants 305

2Al + 3SnO → Al2O3 + 3Sn (2)

ΔG° = RTlnPO2 (3)

4/3Al + O2→ 2/3Al2O3 (4)

'

(5)

) is created. Taking in mind that the

During sintering a microalloying of composite by Sn occurred causing crystal grain surface layer amorphization and a creation of non-stoichiometric phases of Al2O3 with a metal excess [42,43]. In this way, microalloying causes electrochemical activity, which manifests itself in contact with the aqueous solutions of electrolytes and harmful substances in water. Therefore, the ceramics is unstable in contact with water and susceptible to corrosion because surface electrochemical processes taking place. The composite influence redox properties of water and electrochemically

Alumosilicate matrix, whose particles are coated with Al/Sn oxides, was filled with a metal phase which is mostly aluminum with a small quantity of tin as a microalloying component. During the thermal treatment, liquid aluminium simultaneously reacts and penetrates the ceramics preform, resulting in metal/ceramic composite, where the all phases are interpenetrated forming a porous structure. In fact, the reduction of tin(II) occurred

The first reaction step is the reduction of Sn(II) to elemental Sn and its dispersion from the ceramics into the melt. Therefore, during the reaction, Sn is liberated into the liquid metal and diffuses towards the Al source. Moreover, oxygen partial pressure within the composite, at the Al-Al2O3 interface, can be estimated on the basis of thermodynamic

at 900°C, given by Ellingham diagram [44] is -869 KJ/mol, and corresponding oxygen partial pressure: PO2 = 2.02 ∙ 10-39 Pa. Therefore, this low oxygen partial pressure during sintering provides reducing environment and the formation of nonstoichiometric oxide phases, with the metal excess, or with vacancies in oxygen sublattice. Nevertheless, Al2O3 belongs to the oxides of stoichiometric composition or with a negligible deviation from stoichiometry, it can occur as an amorphous and nonstoichiometric oxide with a metal excess during oxidation of aluminium. Common nonstoichiometric reactions occur at low oxygen partial pressures when one of the components (oxygen in this case) leaves the crystal [45,42]. A

(oxygen in this case) leaves the crystal [45,42]. A corresponding defect reaction is [45]:

2 O <sup>1</sup> () V 2 <sup>2</sup> *<sup>x</sup> O Og e <sup>O</sup>*

oxygen is to be presented in neutral form, two resulting electrons would be easily excited

interacts with ionic and colloidal forms of manganese in synthetic water systems.

parameters and calculated using the following equation [44]:

according to the following reaction:

The standard free energy of the reaction:

corresponding defect reaction is [45]:

into the conduction band.

As the oxygen atom escapes, an oxygen vacancy ( VO

Without new materials, there are no new technologies. Having in mind this fact, electrochemically active and structurally modified composites were obtained through microalloying and certain metals hydroxides layering, starting from bentonite as alumosilicate precursor. The composites have prognosed electrochemical, ion-exchanging and adsorption properties, as very sensitive structural and surface properties of materials. After the series of experiments, including composites interaction with synthetic waters, the obtained results are presented, analyzed and then systematized in the form of appropriate models of interactions.

## **8.1. Alumosilicate composite ceramic microalloyed by Sn for the removal of ionic and colloidal forms of Mn**

Usually, manganese does not present a health hazard in the household water supply. However, it can affect the flavor and color of water because it typically causes brownishblack staining of laundry, dishes and glassware [32]. Although manganese is one of the elements that are at least toxic, concentrations of manganese much higher than the maximum allowed concentration during long-term exposure can cause health damage. A number of known procedures for the manganese removal are not suitable for an elimination of its all chemical species due to reversible release of manganese into water systems. Therefore, some of these used procedures are at the edge of techno-economical viability. In order to remove ionic and colloidal forms of manganese, a new aluminosilicate-based ceramic composite with defined electrochemical activity was synthesized [41]. Synthesis procedure of the composite material consists of two phases. Firstly, composite particles were synthesized by applying Al/Sn oxide coating on the bentonite particles in an aqueous suspension. In the second phase, aluminium powder was added to the previously obtained plastic mass and after shaping in the form of spheres 1 cm in diameter and drying, sintering was performed at 900°C. Fig. 1 a), b) and c) presents the microstructure of composite by using different magnifications.

**Figure 1.** SEM images of the composite recorded at: a) low, b) medium and b) high magnifications.

During sintering a microalloying of composite by Sn occurred causing crystal grain surface layer amorphization and a creation of non-stoichiometric phases of Al2O3 with a metal excess [42,43]. In this way, microalloying causes electrochemical activity, which manifests itself in contact with the aqueous solutions of electrolytes and harmful substances in water. Therefore, the ceramics is unstable in contact with water and susceptible to corrosion because surface electrochemical processes taking place. The composite influence redox properties of water and electrochemically interacts with ionic and colloidal forms of manganese in synthetic water systems.

Alumosilicate matrix, whose particles are coated with Al/Sn oxides, was filled with a metal phase which is mostly aluminum with a small quantity of tin as a microalloying component. During the thermal treatment, liquid aluminium simultaneously reacts and penetrates the ceramics preform, resulting in metal/ceramic composite, where the all phases are interpenetrated forming a porous structure. In fact, the reduction of tin(II) occurred according to the following reaction:

$$\text{2Al} + \text{3SnO} \rightarrow \text{AlAlO} + \text{3Sn} \tag{2}$$

The first reaction step is the reduction of Sn(II) to elemental Sn and its dispersion from the ceramics into the melt. Therefore, during the reaction, Sn is liberated into the liquid metal and diffuses towards the Al source. Moreover, oxygen partial pressure within the composite, at the Al-Al2O3 interface, can be estimated on the basis of thermodynamic parameters and calculated using the following equation [44]:

$$
\Delta \mathbf{G}^{\odot} = \text{RTlnPO2} \tag{3}
$$

The standard free energy of the reaction:

304 Composites and Their Applications

models of interactions.

**ionic and colloidal forms of Mn** 

using different magnifications.

**of harmful heavy metals from water** 

**8. New alumosilicate based composites chemically modified by** 

**coatings/thin layers – Tested in the removal of colloidal and ionic forms** 

Without new materials, there are no new technologies. Having in mind this fact, electrochemically active and structurally modified composites were obtained through microalloying and certain metals hydroxides layering, starting from bentonite as alumosilicate precursor. The composites have prognosed electrochemical, ion-exchanging and adsorption properties, as very sensitive structural and surface properties of materials. After the series of experiments, including composites interaction with synthetic waters, the obtained results are presented, analyzed and then systematized in the form of appropriate

**8.1. Alumosilicate composite ceramic microalloyed by Sn for the removal of** 

**Figure 1.** SEM images of the composite recorded at: a) low, b) medium and b) high magnifications.

Usually, manganese does not present a health hazard in the household water supply. However, it can affect the flavor and color of water because it typically causes brownishblack staining of laundry, dishes and glassware [32]. Although manganese is one of the elements that are at least toxic, concentrations of manganese much higher than the maximum allowed concentration during long-term exposure can cause health damage. A number of known procedures for the manganese removal are not suitable for an elimination of its all chemical species due to reversible release of manganese into water systems. Therefore, some of these used procedures are at the edge of techno-economical viability. In order to remove ionic and colloidal forms of manganese, a new aluminosilicate-based ceramic composite with defined electrochemical activity was synthesized [41]. Synthesis procedure of the composite material consists of two phases. Firstly, composite particles were synthesized by applying Al/Sn oxide coating on the bentonite particles in an aqueous suspension. In the second phase, aluminium powder was added to the previously obtained plastic mass and after shaping in the form of spheres 1 cm in diameter and drying, sintering was performed at 900°C. Fig. 1 a), b) and c) presents the microstructure of composite by

$$\text{4/3Al} + \text{Oz} \xrightarrow{} \text{2/3AlzOz} \tag{4}$$

at 900°C, given by Ellingham diagram [44] is -869 KJ/mol, and corresponding oxygen partial pressure: PO2 = 2.02 ∙ 10-39 Pa. Therefore, this low oxygen partial pressure during sintering provides reducing environment and the formation of nonstoichiometric oxide phases, with the metal excess, or with vacancies in oxygen sublattice. Nevertheless, Al2O3 belongs to the oxides of stoichiometric composition or with a negligible deviation from stoichiometry, it can occur as an amorphous and nonstoichiometric oxide with a metal excess during oxidation of aluminium. Common nonstoichiometric reactions occur at low oxygen partial pressures when one of the components (oxygen in this case) leaves the crystal [45,42]. A corresponding defect reaction is [45]:

(oxygen in this case) leaves the crystal [45,42]. A corresponding defect reaction is [45]:

$$\text{O}\_{\text{O}}^{x} \overset{\text{I}}{\underset{\text{2}}{\rightleftharpoons}} \text{O}\_{2}(\text{g}) + \text{ V}\_{\text{O}}^{\bullet \bullet} + 2e^{\cdot} \tag{5}$$

As the oxygen atom escapes, an oxygen vacancy ( VO ) is created. Taking in mind that the oxygen is to be presented in neutral form, two resulting electrons would be easily excited into the conduction band.

Al–Sn alloys show a great activity compared to the thermodynamic Al3+/Al potential of −1.66V vs. NHE, which stands for a pure aluminium. The activation is manifested by a shifting of the pitting potential in the negative direction and significant reducing of the passive potential region [43,46]. The addition of microalloying Sn to aluminium produced a considerable shift of the open circuit potential (OCP) in the negative direction [46].

During the process of composite ceramics sintering, significant changes in the structure of alumosilicate matrix were occurred. Namely, the polycrystaline alumosilicate matrix with amorphised grain and sub-grain boundary were obtained, where a main role possesses metallic aluminum itself, then a microalloyed tin and nonstoichiometric excess of these elements in ceramics, creating macro-, meso- and micro- pores with the reduced mobility of grain boundaries and termination of grain growth [47]. Aluminum and tin in conjunction with other admixtures present in composite ceramics cause drastic changes in the structure-sensitive properties and electrochemical activity. An active composite ceramics in contact with synthetic water containing manganese reduce and deposit the manganese in the macro-, meso- and micro- pores (eq. 6). Electrochemical activity is provided by electrochemical potential of Al atoms and free electrons that participate in redox processes.

$$2\text{Al} + 3\text{Mn}^{2+} \rightarrow 2\text{Al}^{3+} + 3\text{Mn} \tag{6}$$

New Composite Materials in the Technology

for Drinking Water Purification from Ionic and Colloidal Pollutants 307

**Figure 2.** Redox potential of water dependence on pH during interaction of the composite with distilled

**Figure 3.** Percentage removal of Mn2+ (A) and colloidal MnO2 (B) from synthetic waters (the composite dosage, 2 g/dm3; contacting time, 20 min; initial Mn concentrations in range 0.25 – 10 mg/dm3; initial pH

Average initial pH of the synthetic waters was 5.75. After 20 min of contact with the

During the interactions of composite with synthetic waters, the colloidal MnO2 was removed to a lesser degree than Mn2+. The authors imposed that colloidal manganese

{m[MnO2]nSO42- 2(n-x)K+}2xK+ (7)

water.

5.75 ± 0.1; temperature, 20 ± 0.5°C).

composite material average pH was 6.70.

possesses the following structure of micelles:

The deposited manganese on microcathode parts of the structure can further form separate clusters and the adsorption layer [48,49]. Reduction processes take place until the Al3+ ions continue to solvate themselves in water. A part of Al3+ ions reacts with OH ions giving insoluble Al(OH)3.

## *8.1.1. Interaction of composite material with ionic and colloidal forms of Mn in synthetic water*

Interaction of the composite material with water manifests itself as decreasing in the redox potential of water, as shown in Fig. 2. This confirms the fact that the composite is electrochemically active in contact with water. During the interaction with water, aluminium from the composite is electrochemically dissolved into water providing electrons which can participate in the number of redox reactions of water yielding reduced species (molecules, ions and radicals) such as H2, OH , etc. [47].

TDS value of distilled water immediately after contact with ceramics increases. It seems that increasing the TDS value is due to dissolution of Al3+, Mg2+, Na+, SiO32- from the bentonite based composite. Al3+ and SiO32- ions are subjected to hydrolysis and polymerization reactions which are followed by spontaneous coagulation-flocculation processes and appearance of sludge after a prolonged period of time.

A reduction of manganese concentration in synthetic waters is shown in Fig. 3.

direction [46].

redox processes.

insoluble Al(OH)3.

*water* 

Al–Sn alloys show a great activity compared to the thermodynamic Al3+/Al potential of −1.66V vs. NHE, which stands for a pure aluminium. The activation is manifested by a shifting of the pitting potential in the negative direction and significant reducing of the passive potential region [43,46]. The addition of microalloying Sn to aluminium produced a considerable shift of the open circuit potential (OCP) in the negative

During the process of composite ceramics sintering, significant changes in the structure of alumosilicate matrix were occurred. Namely, the polycrystaline alumosilicate matrix with amorphised grain and sub-grain boundary were obtained, where a main role possesses metallic aluminum itself, then a microalloyed tin and nonstoichiometric excess of these elements in ceramics, creating macro-, meso- and micro- pores with the reduced mobility of grain boundaries and termination of grain growth [47]. Aluminum and tin in conjunction with other admixtures present in composite ceramics cause drastic changes in the structure-sensitive properties and electrochemical activity. An active composite ceramics in contact with synthetic water containing manganese reduce and deposit the manganese in the macro-, meso- and micro- pores (eq. 6). Electrochemical activity is provided by electrochemical potential of Al atoms and free electrons that participate in

The deposited manganese on microcathode parts of the structure can further form separate clusters and the adsorption layer [48,49]. Reduction processes take place until the Al3+ ions

*8.1.1. Interaction of composite material with ionic and colloidal forms of Mn in synthetic* 

Interaction of the composite material with water manifests itself as decreasing in the redox potential of water, as shown in Fig. 2. This confirms the fact that the composite is electrochemically active in contact with water. During the interaction with water, aluminium from the composite is electrochemically dissolved into water providing electrons which can participate in the number of redox reactions of water yielding reduced species

TDS value of distilled water immediately after contact with ceramics increases. It seems that increasing the TDS value is due to dissolution of Al3+, Mg2+, Na+, SiO32- from the bentonite based composite. Al3+ and SiO32- ions are subjected to hydrolysis and polymerization reactions which are followed by spontaneous coagulation-flocculation processes and

A reduction of manganese concentration in synthetic waters is shown in Fig. 3.

continue to solvate themselves in water. A part of Al3+ ions reacts with OH-

(molecules, ions and radicals) such as H2, OH , etc. [47].

appearance of sludge after a prolonged period of time.

2Al + 3Mn2+ 2Al3+ + 3Mn (6)

ions giving

**Figure 2.** Redox potential of water dependence on pH during interaction of the composite with distilled water.

**Figure 3.** Percentage removal of Mn2+ (A) and colloidal MnO2 (B) from synthetic waters (the composite dosage, 2 g/dm3; contacting time, 20 min; initial Mn concentrations in range 0.25 – 10 mg/dm3; initial pH 5.75 ± 0.1; temperature, 20 ± 0.5°C).

Average initial pH of the synthetic waters was 5.75. After 20 min of contact with the composite material average pH was 6.70.

During the interactions of composite with synthetic waters, the colloidal MnO2 was removed to a lesser degree than Mn2+. The authors imposed that colloidal manganese possesses the following structure of micelles:

$$\{\text{m}[\text{M} \text{r} \text{O} \text{l}] \text{n} \text{S} \text{O} \text{r}^2 \text{ }^\circ \text{2(n-x)} \text{K}^+ \} 2 \text{xK}^+ \tag{7}$$

Potential-determining ions in the structure of micelles are SO42-. They are primarily adsorbed on MnO2 and responsible for the stability of colloids. Therefore, it is clear that the reduction of manganese is more difficult and there is an electrostatic repulsion between colloidal particles and a composite with dominantly negatively charged surface sites. Thus, the removal efficiency of colloidal manganese is significantly lower compared with the ionic form of Mn+2. During the electrochemical interactions of synthetic water containing Mn2+ and colloidal MnO2 with the composite material, transferring of Al3+ ions in a solution increases the TDS value, as shown in Table 1.

New Composite Materials in the Technology

(8)

(14)

(9)

for Drinking Water Purification from Ionic and Colloidal Pollutants 309

water. Water reduction at cathodic parts of composite (eq. 8), the electrochemical dissolution

2Al + 6H2O 2Al3+ + 3H2 + 6 OH-

Al(OH)4- + H+ Al(OH)3 + H2O (10)

Al(OH)3 + H+ Al(OH)2+ + H2O (11)

Al(OH)2+ + H+ Al(OH)2++ H2O (12)

Al(OH)2+ + H+ Al3+ + H2O (13)

**8.2. Bentonite modified by mixed Fe, Mg (hydr)oxides coatings for the removal** 

Lead (Pb) is heavy metal which presents one of the major environmental pollutants due to its hazardous nature. It diffuses into water and the environment through effluents from lead smelters as well as from battery, paper, pulp and ammunition industries. Scientists established that lead is nonessential for plants and animals, while for humans it is a cumulative poison which can cause damage to the brain, red blood cells and kidneys [52].

In this subchapter, a cheap and effective composite material as a potentially attractive adsorbent for the treatment of Pb(II) contaminated water sources has been described. The procedure for obtaining a bentonite based composite involves the application of mixed Fe and Mg hydroxides coatings onto bentonite particles (0.375 mmol Fe and 0.125 mmol Mg per gram of bentonite) in aqueous suspension and subsequent thermal treatment of the solid phase at 498 K [53]. Bearing in mind layered structure of montmorillonite, the quite limited extent of isomorphous substitution of Mg for Fe in iron (hidr)oxides and significant differences in acid-base surface properties between these two (hydr)oxides, formation of heterogeneous coatings onto bentonite and specific structure of obtained composite have been achieved [54]. Different adsorption sites on such heterogeneous surface provide

The structural changes of montmorillonite during composite synthesis are mainly reflected in the reduction of d001 diffraction peak intensity in X-ray diffractograms and its shifting towards the higher values of 2θ. Moreover, it can be observed that the peak is broadened suggesting that the distance between the layers is non-uniform with disordered and partially delaminated structure. The crystallographic spacing d001 of montmorillonite in the native bentonite and the composite, computed by using Bragg's equation (nλ = 2d sin θ), is 1.54 nm and 1.28 nm, respectively. These changes in the structure took place because the d-spacing is very sensitive

efficient removal of numerous chemical species of Pb(II) over a wide pH range.

to the type of interlamellar cations, and the degree of their hydration [55].

of aluminum (eq. 9) and protolytic reactions (eq. 10-14) increase the pH value [51].

H2O + e- 1/2H2 + OH-

Al(OH)3(s) Al3+ + 3OH-

**of ionic and colloidal forms of Pb(II)** 


**Table 1.** The results of synthetic waters analysis before and after treatment with composite material.

The initial dissolution of the Al based alloys introduces both aluminium and alloying ions into the solution, and then the reposition of microalloying tin onto active sites at surface occurs [46], so it was not detected by ICP-OES analysis.

Aluminium ions generated during electrochemical processes of manganese removal may form monomeric species such as Al(OH)2+, Al(OH)2+ and Al(OH)4- . During the time, these monomers have tendency to polymerize in the pH range 4–7 which results in oversaturation and formation of amorphous hydroxide precipitate according to complex precipitation kinetics. Many polymeric species such as Al6(OH)15+3, Al7(OH)17+4, Al8(OH)20+4, Al13O4(OH)24+7, Al13(OH)34+5 have been reported [50]. Average concentration of aluminium, immediately after 20 min of composite interaction with Mn2+ synthetic waters, was 0.2131 mg/dm3 and included all mentioned monomeric and polymeric species which were not coagulated. After a prolonged period of time concentration of aluminum has a tendency to decrease reaching values that are below 0.1 mg/dm3, due to precipitation of Al(OH)3 sludge.

The increase in the pH during the experiments can be explained in terms of the electrochemical and the chemical reactions that take place in the system composite-synthetic water. Water reduction at cathodic parts of composite (eq. 8), the electrochemical dissolution of aluminum (eq. 9) and protolytic reactions (eq. 10-14) increase the pH value [51].

308 Composites and Their Applications

C0(Mn)

treatment

Al(OH)3 sludge.

increases the TDS value, as shown in Table 1.

Before colloidal MnO2 synthetic water

occurs [46], so it was not detected by ICP-OES analysis.

form monomeric species such as Al(OH)2+, Al(OH)2+ and Al(OH)4-

Potential-determining ions in the structure of micelles are SO42-. They are primarily adsorbed on MnO2 and responsible for the stability of colloids. Therefore, it is clear that the reduction of manganese is more difficult and there is an electrostatic repulsion between colloidal particles and a composite with dominantly negatively charged surface sites. Thus, the removal efficiency of colloidal manganese is significantly lower compared with the ionic form of Mn+2. During the electrochemical interactions of synthetic water containing Mn2+ and colloidal MnO2 with the composite material, transferring of Al3+ ions in a solution

mg/dm3 TDS (mg/dm3) pH C(Mn) mg/dm3 TDS (mg/dm3) pH Before Mn2+ synthetic water treatment After Mn2+ synthetic water treatment 0.25 3 5.75 0.0223 17 6.65 0.50 7 5.73 0.0318 21 6.71 1.0 10 5.71 0.0363 25 6.72 5.0 14 5.70 0.9271 29 6.70 10.0 28 5.76 3.9773 39 6.58

treatment 0.25 3 5.82 0.2108 18 6.73 0.50 6 5.75 0.3928 22 6.71 1.0 11 5.71 0.7366 25 6.72 5.0 14 5.72 3.768 29 6.75 10.0 28 5.75 7.549 39 6.67

**Table 1.** The results of synthetic waters analysis before and after treatment with composite material.

The initial dissolution of the Al based alloys introduces both aluminium and alloying ions into the solution, and then the reposition of microalloying tin onto active sites at surface

Aluminium ions generated during electrochemical processes of manganese removal may

monomers have tendency to polymerize in the pH range 4–7 which results in oversaturation and formation of amorphous hydroxide precipitate according to complex precipitation kinetics. Many polymeric species such as Al6(OH)15+3, Al7(OH)17+4, Al8(OH)20+4, Al13O4(OH)24+7, Al13(OH)34+5 have been reported [50]. Average concentration of aluminium, immediately after 20 min of composite interaction with Mn2+ synthetic waters, was 0.2131 mg/dm3 and included all mentioned monomeric and polymeric species which were not coagulated. After a prolonged period of time concentration of aluminum has a tendency to decrease reaching values that are below 0.1 mg/dm3, due to precipitation of

The increase in the pH during the experiments can be explained in terms of the electrochemical and the chemical reactions that take place in the system composite-synthetic

After colloidal MnO2 synthetic water

. During the time, these

$$\text{H} \text{xO} + \text{e} \rightleftharpoons \text{7} \text{/} 2\text{H} \text{z} + \text{OH} \cdot \text{} \tag{8}$$

$$2\text{Al} + 6\text{H} \bullet \text{\AA} \bullet \text{\AA}^{\text{+}} + 3\text{H} \text{\AA} + 6\text{OH}^{\cdot} \tag{9}$$

$$\text{Al(OH)}\text{ $\text{ $\iota$ }^{\text{-}}\text{ + H}^{\text{+}}\text{ }\mkern-1.1.1.1.1.1.1.1.1.1 \text{--}\text{H}^{\text{-}}\text{ }\text{Al(OH)}\text{---}\text{ }\text{H}^{\text{-}}\text{ }\text{Al}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{H}^{\text{-}}\text{ }\text{-}$ $$

$$\text{Al(OH)}\text{:} + \text{H}^+ \rightleftharpoons \text{Al(OH)}\text{:} + \text{H}\text{:} \text{O} \tag{11}$$

$$\rm Al(OH)\_2^{\cdot} + H^{\cdot} \rightleftharpoons Al(OH)^{2+} + H\_2O \tag{12}$$

$$\rm Al(OH)^{2+} + H^{+} \nrightarrow Al^{3+} + H\_{2}O \tag{13}$$

$$\text{Al(OH):}\\\text{(s)}\\\text{\*} \text{ \* Al}\\\text{\*} + \text{ 3OH}\\\cdot \text{:} \tag{14}$$

## **8.2. Bentonite modified by mixed Fe, Mg (hydr)oxides coatings for the removal of ionic and colloidal forms of Pb(II)**

Lead (Pb) is heavy metal which presents one of the major environmental pollutants due to its hazardous nature. It diffuses into water and the environment through effluents from lead smelters as well as from battery, paper, pulp and ammunition industries. Scientists established that lead is nonessential for plants and animals, while for humans it is a cumulative poison which can cause damage to the brain, red blood cells and kidneys [52].

In this subchapter, a cheap and effective composite material as a potentially attractive adsorbent for the treatment of Pb(II) contaminated water sources has been described. The procedure for obtaining a bentonite based composite involves the application of mixed Fe and Mg hydroxides coatings onto bentonite particles (0.375 mmol Fe and 0.125 mmol Mg per gram of bentonite) in aqueous suspension and subsequent thermal treatment of the solid phase at 498 K [53]. Bearing in mind layered structure of montmorillonite, the quite limited extent of isomorphous substitution of Mg for Fe in iron (hidr)oxides and significant differences in acid-base surface properties between these two (hydr)oxides, formation of heterogeneous coatings onto bentonite and specific structure of obtained composite have been achieved [54]. Different adsorption sites on such heterogeneous surface provide efficient removal of numerous chemical species of Pb(II) over a wide pH range.

The structural changes of montmorillonite during composite synthesis are mainly reflected in the reduction of d001 diffraction peak intensity in X-ray diffractograms and its shifting towards the higher values of 2θ. Moreover, it can be observed that the peak is broadened suggesting that the distance between the layers is non-uniform with disordered and partially delaminated structure. The crystallographic spacing d001 of montmorillonite in the native bentonite and the composite, computed by using Bragg's equation (nλ = 2d sin θ), is 1.54 nm and 1.28 nm, respectively. These changes in the structure took place because the d-spacing is very sensitive to the type of interlamellar cations, and the degree of their hydration [55].

The XRD patterns of the composite and starting (native) bentonite are presented in Fig. 4a and b, respectively.

New Composite Materials in the Technology

for Drinking Water Purification from Ionic and Colloidal Pollutants 311

Cumulative mesopore volume (cm3/g)

Micropore volume (cm3/g)

**Figure 6.** Nitrogen adsorption-desorption isotherms of native bentonite and composite.

Median mesopore diameter (nm)

summarized in Table 2.

Sample SBET (m2/g)

BET, BJH and D-R equation to N2 adsorption at 77 K

The isotherms can be assigned to Type II isotherms, corresponding to non-porous or macroporous adsorbents. The hysteresis loops of Type H3 in the IUPAC classification occur at p/p0 > 0.5, which is not inside the typical BET range. Furthermore, hysteresis loops of these isotherms indicate that they were given by either slit-shaped pores or, as in the present case, assemblages of platy particles of montmorillonite. Porous structure parameters are

Bentonite 37.865 13.629 53.329 0.1202 0.0153 Composite 80.385 11.021 82.675 0.1716 0.0316 **Table 2.** Specific surface area and porosity of native bentonite and composite, determined by applying

Compared to native bentonite, during the composite synthesis additional meso- and micropores were generated. Pore volumes (Gurvich) at p/p0 0.999 for bentonite and composite are 0.180 cm3/g and 0.243 cm3/g, respectively. It was found that isotherms gave linear BET plots from p/p0 0.03 to 0.21 for bentonite and from 0.03 to 0.19 for composite.

The composite has the specific surface area that is twice the size compared to the surface area of the native bentonite. This can be explained by the structural changes that occurred during the chemical and thermal modification of the native bentonite. The structural changes include delamination as well as the decrease of the distance between the layers of montmorillonite particles, because the interlayer water was lost under heating. The higher surface area of composite mainly results from the interparticle spaces generated by the

Cumulative mesopore area (m2/g)

**Figure 4.** X-ray diffractograms of (a) composite and (b) native bentonite

SEM micrographs (Fig. 5 a, b and c) show that bentonite and composite are composed of laminar particles arranged in layered manner, forming the aggregates with diameters up to 50 µm.

**Figure 5.** (a) SEM of synthesized composite, (b) SEM of composite after interaction with Pb(II) solution and (c) surface morphology of the native bentonite

No significant changes in the microstructure of composite occurred during the interaction with the aqueous solution of Pb(II).

Despite a thorough washing process, a large amount of NO3 is retained in the composite. A vibration mode at ca. 1389 cm-1 in FTIR spectrum confirms the NO3- stretching which indicates that some positive charged sites exist on the surface of composite and that they are counterbalanced by the NO3 which can be exchanged by other anions [53]. In addition, the formation of poorly crystallized magnesium hydroxonitrate in pH range 9-11 [56,57], where Fe/Mg coprecipitation was performed over bentonite particles, is very likely.

## *8.2.1. Specific surface area determined by N2 adsorption/desorption using BET equation*

The Fig. 6. shows the comparative nitrogen adsorption-desorption isotherms of native bentonite and composite.

**Figure 6.** Nitrogen adsorption-desorption isotherms of native bentonite and composite.

and b, respectively.

50 µm.

The XRD patterns of the composite and starting (native) bentonite are presented in Fig. 4a

SEM micrographs (Fig. 5 a, b and c) show that bentonite and composite are composed of laminar particles arranged in layered manner, forming the aggregates with diameters up to

**Figure 5.** (a) SEM of synthesized composite, (b) SEM of composite after interaction with Pb(II) solution

No significant changes in the microstructure of composite occurred during the interaction

vibration mode at ca. 1389 cm-1 in FTIR spectrum confirms the NO3- stretching which indicates that some positive charged sites exist on the surface of composite and that they are

formation of poorly crystallized magnesium hydroxonitrate in pH range 9-11 [56,57], where

*8.2.1. Specific surface area determined by N2 adsorption/desorption using BET equation* 

The Fig. 6. shows the comparative nitrogen adsorption-desorption isotherms of native

Fe/Mg coprecipitation was performed over bentonite particles, is very likely.

which can be exchanged by other anions [53]. In addition, the

is retained in the composite. A

**Figure 4.** X-ray diffractograms of (a) composite and (b) native bentonite

and (c) surface morphology of the native bentonite

Despite a thorough washing process, a large amount of NO3-

with the aqueous solution of Pb(II).

counterbalanced by the NO3-

bentonite and composite.

The isotherms can be assigned to Type II isotherms, corresponding to non-porous or macroporous adsorbents. The hysteresis loops of Type H3 in the IUPAC classification occur at p/p0 > 0.5, which is not inside the typical BET range. Furthermore, hysteresis loops of these isotherms indicate that they were given by either slit-shaped pores or, as in the present case, assemblages of platy particles of montmorillonite. Porous structure parameters are summarized in Table 2.


**Table 2.** Specific surface area and porosity of native bentonite and composite, determined by applying BET, BJH and D-R equation to N2 adsorption at 77 K

Compared to native bentonite, during the composite synthesis additional meso- and micropores were generated. Pore volumes (Gurvich) at p/p0 0.999 for bentonite and composite are 0.180 cm3/g and 0.243 cm3/g, respectively. It was found that isotherms gave linear BET plots from p/p0 0.03 to 0.21 for bentonite and from 0.03 to 0.19 for composite.

The composite has the specific surface area that is twice the size compared to the surface area of the native bentonite. This can be explained by the structural changes that occurred during the chemical and thermal modification of the native bentonite. The structural changes include delamination as well as the decrease of the distance between the layers of montmorillonite particles, because the interlayer water was lost under heating. The higher surface area of composite mainly results from the interparticle spaces generated by the three-dimensional co-aggregation of magnesium polyoxocations, iron oxide clusters and plate particles of montmorillonite. Macro- and mesopores arose from particle-to-particle interactions, while micropores were generated in the interlayer spaces of clay minerals due to irregular stacking of layers of different lateral dimensions [58].It is apparent that the changes of montmorillonite structure are responsible for the creation of new pore structure in the composite, which is then stabilized by the thermal treatment with the removal of H2O molecules. The changes that involve partial dehydroxylation and cationic dehydration are brought about by thermal activation and they lead to various forms of cross-linking between oxides and smectite framework. As a result, composite does not swell and can be easily separated from water by filtration or centrifugation. There is a wide pore size distribution which supports disordered structure consisting of the delaminated parts with mesoporosity and the layered parts with microporosity.

New Composite Materials in the Technology

∙(n-x)Na+}xNa+ (16)

for Drinking Water Purification from Ionic and Colloidal Pollutants 313

which give rise to the formation of negatively charged colloidal

The potential – determining ion is Pb(OH)+ and that is the reason for the positive ZP of colloidal Pb(II) at the pH below 10 [59,60]. Therefore, colloidal micelles were easily attracted by the negatively charged composite surface. Particle size of colloidal Pb(II) at pH 7±0.1 was determined to be 268.7 ± 16.7 nm. At the pH range of 10-12 the predominant Pb(II) species

ZP values for Pb(II) colloidal solutions at pH 11.8 were - 50.7±3.6 mV with particle size of 252.7±28.2 nm. Having in mind surface heterogeneity of the composite and high point of zero charge value of Mg(OH)2 (between pH 12 and pH 13) [61], negative ions and particles can be adsorbed on the positively charged surface sites at pH 10-12. Removal efficiency of

were involved in the process of ion exchange and chemisorption, while colloidal micelles

Synthesis of bentonite based composite material, described in this section, was carried out by applying thin coatings of natural organic matter, obtained by alkaline extraction from peat, mostly comprised of humic acids [62]. Humic acids have high complexing ability with various heavy metal ions, but it is difficult to use them as the sorbent because of their high solubility in water. However, they form stabile complexes with the inorganic ingredients of bentonite (montmorillonite, quartz, oxides, etc.) and can be additionally insolubilized and immobilized by heating at 350°C. After immobilization, humic acids represent an important sorbent for heavy metals, pesticides and other harmful ingredients from water. Humic acid are insolubilized by condensation of carboxylic and phenolic hydroxyl groups. Therefore, the aim was to remove manganese from aqueous solutions by treating it with synthesized composite as well as to study and explain the mechanism of composite interaction with manganese aqueous solutions. The composite does not release significant quantity of organic matter in water because it is tightly bonded to bentonite surface [63-65]. The degree of manganese removal was more than 94% at a range of initial manganese concentrations

The result of conductometric titration is given in Fig. 8. Equivalence point was located at the intercept of the first and second linear part of the titration curve. The value of the total acidic

The experimental data of manganese adsorption onto composite are very well fitted by the Freundlich isotherm model (Fig. 9.) with a very high correlation coefficient value of 0.9948. The good agreement of experimental data with the Freundlich model indicates that there are several types of adsorption sites on the surface of the composite. The amount of adsorbed Mn(II) increases rapidly in the first region of adsorption isotherm and then the slope of

**8.3. Bentonite based composite coated with immobilized thin layer of organic** 

was higher than negatively charged colloids, probably because the ionic species

are Pb(OH)2 and Pb(OH)3-

Pb(OH)3-

**matter** 

from 0.250 to 10 mg/l.

group content is calculated to be 215.18 µmol/g.

micelles with the following structure:

{m[Pb(OH)2]nPb(OH)3-

could be bound to the surface dominantly by electrostatic forces.

The pH of the Pb(II) solution plays an important role in the adsorption process, influencing not only the surface charge of the adsorbent and the dissociation of functional groups on the active sites of the adsorbent but also the solution Pb(II) chemistry. The adsorption of Pb(II) on the composite decreased when pH decreased as shown in Fig. 7.

**Figure 7.** Effect of pH on adsorption of Pb(II) onto composite

The adsorptive decrease at pH below 5 was caused by the competition between H+ and Pb2+ for the negatively charged surface sites. Maximum retention is in the pH range 5-10. The main Pb(II) species in the pH range 6.5-10 are Pb(OH)+ and Pb(OH)2 which can easily form colloidal micelles characterized with the following imposed structure:

$$\langle \text{m} \vert \text{Pb(OH)} \rangle \text{lnPb(OH)}^{\cdot} \cdot \text{(n-x)NO} \cdot \text{xNOc} \tag{15}$$

The potential – determining ion is Pb(OH)+ and that is the reason for the positive ZP of colloidal Pb(II) at the pH below 10 [59,60]. Therefore, colloidal micelles were easily attracted by the negatively charged composite surface. Particle size of colloidal Pb(II) at pH 7±0.1 was determined to be 268.7 ± 16.7 nm. At the pH range of 10-12 the predominant Pb(II) species are Pb(OH)2 and Pb(OH)3 which give rise to the formation of negatively charged colloidal micelles with the following structure:

312 Composites and Their Applications

and the layered parts with microporosity.

three-dimensional co-aggregation of magnesium polyoxocations, iron oxide clusters and plate particles of montmorillonite. Macro- and mesopores arose from particle-to-particle interactions, while micropores were generated in the interlayer spaces of clay minerals due to irregular stacking of layers of different lateral dimensions [58].It is apparent that the changes of montmorillonite structure are responsible for the creation of new pore structure in the composite, which is then stabilized by the thermal treatment with the removal of H2O molecules. The changes that involve partial dehydroxylation and cationic dehydration are brought about by thermal activation and they lead to various forms of cross-linking between oxides and smectite framework. As a result, composite does not swell and can be easily separated from water by filtration or centrifugation. There is a wide pore size distribution which supports disordered structure consisting of the delaminated parts with mesoporosity

The pH of the Pb(II) solution plays an important role in the adsorption process, influencing not only the surface charge of the adsorbent and the dissociation of functional groups on the active sites of the adsorbent but also the solution Pb(II) chemistry. The adsorption of Pb(II)

The adsorptive decrease at pH below 5 was caused by the competition between H+ and Pb2+ for the negatively charged surface sites. Maximum retention is in the pH range 5-10. The main Pb(II) species in the pH range 6.5-10 are Pb(OH)+ and Pb(OH)2 which can easily form

}xNO3-

(15)

on the composite decreased when pH decreased as shown in Fig. 7.

**Figure 7.** Effect of pH on adsorption of Pb(II) onto composite

colloidal micelles characterized with the following imposed structure:

{m[Pb(OH)2]nPb(OH)+∙(n-x)NO3-

$$\{\text{m}[\text{Pb(OH)}\text{x}]\text{nPb(OH)}\text{y} \cdot (\text{n-x})\text{Na}^{+}\} \text{xNa}^{+}\tag{16}$$

ZP values for Pb(II) colloidal solutions at pH 11.8 were - 50.7±3.6 mV with particle size of 252.7±28.2 nm. Having in mind surface heterogeneity of the composite and high point of zero charge value of Mg(OH)2 (between pH 12 and pH 13) [61], negative ions and particles can be adsorbed on the positively charged surface sites at pH 10-12. Removal efficiency of Pb(OH)3 was higher than negatively charged colloids, probably because the ionic species were involved in the process of ion exchange and chemisorption, while colloidal micelles could be bound to the surface dominantly by electrostatic forces.

## **8.3. Bentonite based composite coated with immobilized thin layer of organic matter**

Synthesis of bentonite based composite material, described in this section, was carried out by applying thin coatings of natural organic matter, obtained by alkaline extraction from peat, mostly comprised of humic acids [62]. Humic acids have high complexing ability with various heavy metal ions, but it is difficult to use them as the sorbent because of their high solubility in water. However, they form stabile complexes with the inorganic ingredients of bentonite (montmorillonite, quartz, oxides, etc.) and can be additionally insolubilized and immobilized by heating at 350°C. After immobilization, humic acids represent an important sorbent for heavy metals, pesticides and other harmful ingredients from water. Humic acid are insolubilized by condensation of carboxylic and phenolic hydroxyl groups. Therefore, the aim was to remove manganese from aqueous solutions by treating it with synthesized composite as well as to study and explain the mechanism of composite interaction with manganese aqueous solutions. The composite does not release significant quantity of organic matter in water because it is tightly bonded to bentonite surface [63-65]. The degree of manganese removal was more than 94% at a range of initial manganese concentrations from 0.250 to 10 mg/l.

The result of conductometric titration is given in Fig. 8. Equivalence point was located at the intercept of the first and second linear part of the titration curve. The value of the total acidic group content is calculated to be 215.18 µmol/g.

The experimental data of manganese adsorption onto composite are very well fitted by the Freundlich isotherm model (Fig. 9.) with a very high correlation coefficient value of 0.9948. The good agreement of experimental data with the Freundlich model indicates that there are several types of adsorption sites on the surface of the composite. The amount of adsorbed Mn(II) increases rapidly in the first region of adsorption isotherm and then the slope of isotherm gradually decreases in the second region. The adsorption capacity of composite is 11.86 mg/g, at an equilibrium manganese concentration of 16.28 mg/l.

New Composite Materials in the Technology

)2...Mn2+ + (3-n) Cn+ (17)

≡S-OH + Mn2+ ⇌ ≡S-O-Mn+ + H+ (18)

≡2S-OH + Mn2+ ⇌ (≡S-O)2-Mn + 2H+ (19)

for Drinking Water Purification from Ionic and Colloidal Pollutants 315

**Figure 9.** Freundlich adsorption isotherm for manganese adsorption onto composite.

including ion exchange, can be showed by an Eq. (17) [66].

in which C represents the cation that is exchanged.

(≡S-O-

During the thermal treatment in nitrogen atmosphere at 350 °C, the condensation of carboxyl and adjacent alcohol and phenol groups occurs. In this way the solubility of organic matter immobilized on bentonite matrix surface decreases [65]. Moreover, a part of carboxyl groups is decomposed by decarboxylation reaction, releasing CO2 and CO. However, despite of this, a part of oxygen functional groups remains on the surface, and these groups act as sites that bind bivalent manganese forming inner-sphere complexes.

Besides organic functional groups, there are also Si-OH and Al-OH groups on the sites of crystal grain breaks, as well as permanent negative charge due to isomorphic substitution in clay minerals. They all contribute to the reduction of manganese concentration in the aqueous solution. Manganese retention by the formation of outer-sphere complexes,

The formation of inner-sphere complexes is represented by the Eqs. (18) and (19) and

According to these equations, it can be concluded that the pH value of the solutions decrease after the treatment. However, an opposite phenomenon can be experimentally observed (Table 3). The explanation for it is that hydrogen ions which are released during

)2...Cn+3-n + Mn2+ ⇌ (≡S-O-

involves the release of hydrogen ions and the change of solution pH.

manganese retention participate in the protonation of surface groups:

**Figure 8.** The conductometric titration of composite suspension (1 g in 250 ml of 1mM NaCl solution as background electrolyte) with 0.053 M NaOH.

After the treatment of model water with composite for the period of 20 min, the following results were obtained (Table 3).


**Table 3.** The results of water analysis before and after treatment with composite

**Figure 9.** Freundlich adsorption isotherm for manganese adsorption onto composite.

During the thermal treatment in nitrogen atmosphere at 350 °C, the condensation of carboxyl and adjacent alcohol and phenol groups occurs. In this way the solubility of organic matter immobilized on bentonite matrix surface decreases [65]. Moreover, a part of carboxyl groups is decomposed by decarboxylation reaction, releasing CO2 and CO. However, despite of this, a part of oxygen functional groups remains on the surface, and these groups act as sites that bind bivalent manganese forming inner-sphere complexes.

Besides organic functional groups, there are also Si-OH and Al-OH groups on the sites of crystal grain breaks, as well as permanent negative charge due to isomorphic substitution in clay minerals. They all contribute to the reduction of manganese concentration in the aqueous solution. Manganese retention by the formation of outer-sphere complexes, including ion exchange, can be showed by an Eq. (17) [66].

$$(\mathfrak{w}\mathbb{S}\cdot\mathcal{O})\sharp\ldots\mathbb{C}^{n\star\_{3n}} + \mathrm{Mn^{2+}} \rightleftharpoons (\mathfrak{w}\mathbb{S}\cdot\mathcal{O})\sharp\ldots\mathrm{Mn^{2+}} + (\mathfrak{Z}\cdot\mathfrak{n})\,\mathrm{C}^{n\star} \tag{17}$$

in which C represents the cation that is exchanged.

314 Composites and Their Applications

background electrolyte) with 0.053 M NaOH.

Before water treatment After water treatment

results were obtained (Table 3).

g/l pH Conductivity

C0(Mn)m

isotherm gradually decreases in the second region. The adsorption capacity of composite is

**Figure 8.** The conductometric titration of composite suspension (1 g in 250 ml of 1mM NaCl solution as

After the treatment of model water with composite for the period of 20 min, the following

µS/cm pH Conductivity

0 6.43 8.01 6.67 11.43 0 0

0.250 6.37 9.57 7.11 13.76 0.0030 98.8 0.490 6.32 10.67 7.15 15.31 0.0039 99.2 1.0 6.30 14.67 7.12 31.10 0.0090 99.1

2.5 6.20 20.70 6.96 37.20 0.0187 99.25 5.0 6.19 32.80 6.83 49.40 0.0646 98.71 10.0 6.16 55.30 6.70 68.90 0.5314 94.69

**Table 3.** The results of water analysis before and after treatment with composite

µS/cm C(Mn) mg/l %Mn

Adsorption

11.86 mg/g, at an equilibrium manganese concentration of 16.28 mg/l.

The formation of inner-sphere complexes is represented by the Eqs. (18) and (19) and involves the release of hydrogen ions and the change of solution pH.

$$\text{\#S-OH} + \text{Mn}^{2+} \rightleftharpoons \text{\#S-O-Mn^{+}} + \text{H}^{+} \tag{18}$$

$$\text{\textbullet2S-OH} + \text{Mn}^{2+} \rightleftharpoons \text{(\#S-O)} \text{\textbullet Mn} + 2\text{H}^{+} \tag{19}$$

According to these equations, it can be concluded that the pH value of the solutions decrease after the treatment. However, an opposite phenomenon can be experimentally observed (Table 3). The explanation for it is that hydrogen ions which are released during manganese retention participate in the protonation of surface groups:

$$\text{\#S-OH} + \text{H}^+ \rightleftharpoons \text{\#S-OH} 2^+ \tag{20}$$

New Composite Materials in the Technology

for Drinking Water Purification from Ionic and Colloidal Pollutants 317

**Figure 11.** Premanganate number and turbidity of filtrate as function of pH (0.2 g of composite and 100

The widespread industrial areas where nanocomposites can be applied are primary and conversion industry, modern coating technologies, constructional regions, and environmental (water, air) purification. In addition to the dominant use of composites as structural elements, important application of composite materials is in the water purification technologies. In this field of application, composites usually have the role of adsorbent,

Bentonite is a natural and colloidal alumosilicate with particle size less than 10 µm, which is effectively used as sorbent for heavy metals and other inorganic and organic pollutants from water. Due to its positive textural properties and high specific surface area it can be used as low-cost matrix for synthesis of adsorbents or electrochemically active composite materials for the removal of pollutants in ionic and colloidal form from water. In this respect, three new/modified bentonite based composite materials have been synthetised and characterized.

Coated or composite particles are composed of solid phase covered with thinner or thicker layer of another material. These coatings - layers covering the surface of matrix are important for several reasons. In such way, the surface and textural characteristics of the initial solid phase are modified and sintering conditions can be better controlled. An important factor in achieving the desired microstructure of ceramics is sintering procedure that includes rather complex processes. A considerable influence on sintering has been exhibited by an addition of microalloying components, which significantly determined a

The released organic matter contributes to the increased turbidity at higher pH values.

electrochemically active materials, catalysts, photocatalysts etc.

ml of 1mM Na2SO4 as background electrolyte).

**9. Summary** 

$$\text{H} \triangleq \text{S-O} + \text{H}^+ \rightleftharpoons \text{H-OH} \tag{21}$$

Therefore, the pH value of the Mn2+ aqueous solutions after treatment with composite had a higher value than the initial pH. This indicates that more hydrogen ions are bound to the surface than released by manganese binding. Namely, the composite exhibits amphoteric character due to the surface sites that act either as proton acceptors or as proton donors.

Organic matter decreases the PZC value of bentonite and neutralizes positive electric charge that comes from interlaminated cations, thus increasing composite affinity to manganese, even at lower pH values (67). Fig. 10. presents the pH dependence of residual Mn concentration, for the initial Mn concentration of 5 mg/l. The residual concentration of Mn decreases gradually with pH increasing in the range of 3.5-7 and then increases in the range of 7-10, with the apparent minimum at pH 7.

**Figure 10.** Residual concentration of Mn(II) as a function of model water pH.

The increase of pH value has dual effect on the removal of manganese. The increase of the pH value favours manganese removal due to increase of the number of deprotonated sites that are available for the binding of manganese. However, there is an increase in the solubility of organic matter which has been applied on the bentonite particles. The dissolved organic matter (humic acids) reacts with manganese forming complexes which bear a negative charge and have a weaker binding affinity for the composite surface than Mn2+. Fig 10. indicates two opposite effects of the pH on manganese removal. The pH dependence of released organic matter (expressed as permanganate number) and turbidity (NTU) of solutions are shown in Fig. 11.

#### New Composite Materials in the Technology for Drinking Water Purification from Ionic and Colloidal Pollutants 317

**Figure 11.** Premanganate number and turbidity of filtrate as function of pH (0.2 g of composite and 100 ml of 1mM Na2SO4 as background electrolyte).

The released organic matter contributes to the increased turbidity at higher pH values.

## **9. Summary**

316 Composites and Their Applications

of 7-10, with the apparent minimum at pH 7.

≡S-OH + H+ ⇌ ≡S-OH2+ (20)

+ H+ ⇌ ≡S-OH (21)

≡S-O-

**Figure 10.** Residual concentration of Mn(II) as a function of model water pH.

solutions are shown in Fig. 11.

The increase of pH value has dual effect on the removal of manganese. The increase of the pH value favours manganese removal due to increase of the number of deprotonated sites that are available for the binding of manganese. However, there is an increase in the solubility of organic matter which has been applied on the bentonite particles. The dissolved organic matter (humic acids) reacts with manganese forming complexes which bear a negative charge and have a weaker binding affinity for the composite surface than Mn2+. Fig 10. indicates two opposite effects of the pH on manganese removal. The pH dependence of released organic matter (expressed as permanganate number) and turbidity (NTU) of

Therefore, the pH value of the Mn2+ aqueous solutions after treatment with composite had a higher value than the initial pH. This indicates that more hydrogen ions are bound to the surface than released by manganese binding. Namely, the composite exhibits amphoteric character due to the surface sites that act either as proton acceptors or as proton donors.

Organic matter decreases the PZC value of bentonite and neutralizes positive electric charge that comes from interlaminated cations, thus increasing composite affinity to manganese, even at lower pH values (67). Fig. 10. presents the pH dependence of residual Mn concentration, for the initial Mn concentration of 5 mg/l. The residual concentration of Mn decreases gradually with pH increasing in the range of 3.5-7 and then increases in the range

> The widespread industrial areas where nanocomposites can be applied are primary and conversion industry, modern coating technologies, constructional regions, and environmental (water, air) purification. In addition to the dominant use of composites as structural elements, important application of composite materials is in the water purification technologies. In this field of application, composites usually have the role of adsorbent, electrochemically active materials, catalysts, photocatalysts etc.

> Bentonite is a natural and colloidal alumosilicate with particle size less than 10 µm, which is effectively used as sorbent for heavy metals and other inorganic and organic pollutants from water. Due to its positive textural properties and high specific surface area it can be used as low-cost matrix for synthesis of adsorbents or electrochemically active composite materials for the removal of pollutants in ionic and colloidal form from water. In this respect, three new/modified bentonite based composite materials have been synthetised and characterized.

> Coated or composite particles are composed of solid phase covered with thinner or thicker layer of another material. These coatings - layers covering the surface of matrix are important for several reasons. In such way, the surface and textural characteristics of the initial solid phase are modified and sintering conditions can be better controlled. An important factor in achieving the desired microstructure of ceramics is sintering procedure that includes rather complex processes. A considerable influence on sintering has been exhibited by an addition of microalloying components, which significantly determined a

microstructure and resulted properties of ceramics. The presence of small amounts of impurities in the starting material can vastly influence their mechanical, optical, electrical, color, diffusive, and dielectric properties of alumosilicate matrix. In summary, the process of diffusion mass transport in ceramic crystal regions are affected by temperature, oxygen partial pressure and concentration of impurities. A procedure for the removal of manganese in ionic (Mn2+) and colloidal (MnO2) forms from synthetic waters, by reduction and adsorption processes on electrochemically active alumosilicate ceramics based composite material has been described. Synthesis procedure of the composite material consists of two phases. Firstly, composite particles were synthesized by applying Al/Sn oxide coating onto the bentonite particles in an aqueous suspension. In the second phase, aluminium powder is added to the previously obtained plastic mass and after shaping in the form of spheres 1 cm in diameter and drying, sintering was performed at 900°C. Elemental tin, resulting from the reduction of Sn2+-ion, comes into contact with liquid aluminum in the pores of the matrix performing aluminum microalloying and activation. Moreover, due to a low partial pressure of oxygen, nonstoichiometric oxides with metal excess are obtained, and they play an important role in the electrochemical activity of the composite material. In accordance with this, a redox potential of water is changed in contact with composite.

New Composite Materials in the Technology


for Drinking Water Purification from Ionic and Colloidal Pollutants 319

The authors acknowledge financial support from the Ministry of Education and Science of

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**Acknowledgement** 

the Republic of Serbia.

**10. References** 

Another effective composite material as a potentially attractive adsorbent for the treatment of Pb(II) contaminated water sources has been synthesized by coating of bentonite with mixed iron and magnesium (hydr)oxides. The procedure for obtaining a bentonite based composite involves the application of mixed Fe and Mg hydroxides coatings onto bentonite particles in aqueous suspension and subsequent thermal treatment of the solid phase at 225ºC. Formation of heterogeneous coatings on bentonite results in changes of bentonite acid-based properties, high specific surface area and positive adsorption characteristics. Different adsorption sites on such heterogeneous surface provide an efficient removal of numerous chemical species of Pb(II) (ionic and colloidal) over a wide pH range.

Third bentonite based composite material was obtained by applying thin coatings of natural organic matter, extracted from a peat, mostly based on humic acids. Humic acids are known due to high complexing ability to various heavy metal ions, but it is difficult to use them directly as the sorbent because of their high solubility in water. However, they form stabile complexes with the inorganic ingredients of bentonite (montmorillonite, quartz, oxides, etc.) and can be successfully insolubilized and immobilized by heating at 350°C. After immobilization, humic acids represent an important sorbent for heavy metals, pesticides and other harmful ingredients from water. Humic acid are insolubilized by condensation of carboxylic and phenolic hydroxyl groups. The composite such obtained can be effectively used as the sorbent for heavy metals.

## **Author details**

Marjan S. Ranđelović, Aleksandra R. Zarubica and Milovan M. Purenović *University of Niš, Faculty of Science and Mathematics, Department of Chemistry, Niš, Serbia* 

## **Acknowledgement**

The authors acknowledge financial support from the Ministry of Education and Science of the Republic of Serbia.

## **10. References**

318 Composites and Their Applications

microstructure and resulted properties of ceramics. The presence of small amounts of impurities in the starting material can vastly influence their mechanical, optical, electrical, color, diffusive, and dielectric properties of alumosilicate matrix. In summary, the process of diffusion mass transport in ceramic crystal regions are affected by temperature, oxygen partial pressure and concentration of impurities. A procedure for the removal of manganese in ionic (Mn2+) and colloidal (MnO2) forms from synthetic waters, by reduction and adsorption processes on electrochemically active alumosilicate ceramics based composite material has been described. Synthesis procedure of the composite material consists of two phases. Firstly, composite particles were synthesized by applying Al/Sn oxide coating onto the bentonite particles in an aqueous suspension. In the second phase, aluminium powder is added to the previously obtained plastic mass and after shaping in the form of spheres 1 cm in diameter and drying, sintering was performed at 900°C. Elemental tin, resulting from the reduction of Sn2+-ion, comes into contact with liquid aluminum in the pores of the matrix performing aluminum microalloying and activation. Moreover, due to a low partial pressure of oxygen, nonstoichiometric oxides with metal excess are obtained, and they play an important role in the electrochemical activity of the composite material. In accordance

with this, a redox potential of water is changed in contact with composite.

numerous chemical species of Pb(II) (ionic and colloidal) over a wide pH range.

Marjan S. Ranđelović, Aleksandra R. Zarubica and Milovan M. Purenović

*University of Niš, Faculty of Science and Mathematics, Department of Chemistry, Niš, Serbia* 

used as the sorbent for heavy metals.

**Author details** 

Another effective composite material as a potentially attractive adsorbent for the treatment of Pb(II) contaminated water sources has been synthesized by coating of bentonite with mixed iron and magnesium (hydr)oxides. The procedure for obtaining a bentonite based composite involves the application of mixed Fe and Mg hydroxides coatings onto bentonite particles in aqueous suspension and subsequent thermal treatment of the solid phase at 225ºC. Formation of heterogeneous coatings on bentonite results in changes of bentonite acid-based properties, high specific surface area and positive adsorption characteristics. Different adsorption sites on such heterogeneous surface provide an efficient removal of

Third bentonite based composite material was obtained by applying thin coatings of natural organic matter, extracted from a peat, mostly based on humic acids. Humic acids are known due to high complexing ability to various heavy metal ions, but it is difficult to use them directly as the sorbent because of their high solubility in water. However, they form stabile complexes with the inorganic ingredients of bentonite (montmorillonite, quartz, oxides, etc.) and can be successfully insolubilized and immobilized by heating at 350°C. After immobilization, humic acids represent an important sorbent for heavy metals, pesticides and other harmful ingredients from water. Humic acid are insolubilized by condensation of carboxylic and phenolic hydroxyl groups. The composite such obtained can be effectively


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[52] Lead in Drinking-water, Background document for development of WHO Guidelines for Drinking-water Quality*,* World Health Organization; 2003.

**Chapter 13** 

© 2012 Lu et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

distribution, and reproduction in any medium, provided the original work is properly cited.

© 2012 Lu et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

**Mechanical Coating Technique for Composite** 

**Films and Composite Photocatalyst Films** 

**1.1. Coating techniques for film materials and their applications** 

materials can fall into several categories as shown in Table 1.

comparing with PVD and CVD due to their features.

In the field of materials science and engineering, the investigation on film materials is becoming increasingly important. By film materials, we can develop a variety of new material properties in the fields of electrics and electronics, optics, thermotics, magnetic, and mechanics, among others (S. Yoshida et al., 2008). In recent years, without the development of film materials we could not make any great progress in the renewable energy, environment improvement, exploitation of space, and so on. The coating techniques for film

In these techniques, physical vapor deposition (PVD) and chemical vapor deposition (CVD) are most widely applied. PVD are atomistic deposition processes in which material is vaporized from a solid or liquid source in the form of atoms or molecules and transported in the form of a vapor through a vacuum or low pressure gaseous (or plasma) environment to the substrate, where it condenses. PVD can be used to deposit films of elements and alloys as well as compounds using reactive deposition processes (Mattox, 2010). On the other hand, CVD may be defined as the deposition of a solid on a heated surface from a chemical reaction in the vapor phase. It belongs to the class of vapor-transfer processes which is atomistic in nature, which is the deposition species are atoms or molecules or a combined of these (Pierson, 1999). Microfabrication processes widely use CVD to deposit film materials in various forms including monocrystalline, polycrystalline, amorphous and epitaxial depending on the deposition materials and the reaction conditions. As listed in Table 1, there are other coating techniques for film materials such as liquid absorption coating, thermal spraying and mechanical coating. However, their applications are narrow

Yun Lu, Liang Hao and Hiroyuki Yoshida

http://dx.doi.org/10.5772/48794

**1. Introduction** 

Additional information is available at the end of the chapter


## **Mechanical Coating Technique for Composite Films and Composite Photocatalyst Films**

Yun Lu, Liang Hao and Hiroyuki Yoshida

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/48794

## **1. Introduction**

322 Composites and Their Applications

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for Drinking-water Quality*,* World Health Organization; 2003.

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contaminant sorption of clay minerals. Chemosphere 2002; 49 619-628.

## **1.1. Coating techniques for film materials and their applications**

In the field of materials science and engineering, the investigation on film materials is becoming increasingly important. By film materials, we can develop a variety of new material properties in the fields of electrics and electronics, optics, thermotics, magnetic, and mechanics, among others (S. Yoshida et al., 2008). In recent years, without the development of film materials we could not make any great progress in the renewable energy, environment improvement, exploitation of space, and so on. The coating techniques for film materials can fall into several categories as shown in Table 1.

In these techniques, physical vapor deposition (PVD) and chemical vapor deposition (CVD) are most widely applied. PVD are atomistic deposition processes in which material is vaporized from a solid or liquid source in the form of atoms or molecules and transported in the form of a vapor through a vacuum or low pressure gaseous (or plasma) environment to the substrate, where it condenses. PVD can be used to deposit films of elements and alloys as well as compounds using reactive deposition processes (Mattox, 2010). On the other hand, CVD may be defined as the deposition of a solid on a heated surface from a chemical reaction in the vapor phase. It belongs to the class of vapor-transfer processes which is atomistic in nature, which is the deposition species are atoms or molecules or a combined of these (Pierson, 1999). Microfabrication processes widely use CVD to deposit film materials in various forms including monocrystalline, polycrystalline, amorphous and epitaxial depending on the deposition materials and the reaction conditions. As listed in Table 1, there are other coating techniques for film materials such as liquid absorption coating, thermal spraying and mechanical coating. However, their applications are narrow comparing with PVD and CVD due to their features.

© 2012 Lu et al., licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Lu et al., licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.


Mechanical Coating Technique for Composite Films and Composite Photocatalyst Films 325

Large and complex equipment Coating on flat substrate

Large and complex equipment Elevated temperature process

Complicated post treatment Elevated temperature process

Elevated temperature process

Large and complex equipment Coating on flat substrate

Grain growth

technique Advantages Limitations

Large area coating

Simple equipment

Large specific area

Nanoscale coating

**Table 2.** Advantages and limitations of the film coating techniques

**2. A novel coating technique for composite films** 

*2.1.1. Contamination phenomena during Mechanical Alloying (MA)* 

*2.1.2. Concept proposal of mechanical coating technique (MCT)* 

Powder metallurgy has been widely used in the manufacturing of mechanical parts. A typical process of powder metallurgy is shown in Fig. 1. As shown in the schematic diagram, blending of powder particles is necessary before compacting. Ball milling is often used to mix powder particles and make them homogeneous. Mechanical alloying, well known as ball milling, is frequently used to improve various material properties and to prepare advanced materials that are different or impossible to be obtained by traditional techniques (Suryanarayana, 2001). Ceramic balls are often used as grinding mediums which are indispensable in MA. However, the contamination of powder from grinding mediums and the adhesion of powder particles to the grinding mediums always harass engineers. Especially, the adhesion of powder particles to the grinding mediums and the bowl is really

From the contamination discussed above, we proposed a novel film coating technique in 2005 called mechanical coating technique (MCT) with the diagram schematic shown in Fig. 2 (Lu et al., 2005). In this technique, metal powder and ceramic grinding mediums (balls, buttons and columns) are used as the coating material and the substrates respectively. Firstly, they are charged into a bowl made of alumina. The mechanical coating is performed by a pot mill or a planetary ball mill. In the process, friction, wear and impact among metal powder particles, ceramic grinding mediums and the inner wall of the bowl occur. That results in the formation of metal films on ceramic grinding mediums. In fact, some other

Coating on complex substrate

CVD Coating on complex substrate Strong adhesion

Film coating

Liquid absorption coating

difficult to be eliminated.

PVD Thickness control

Thermal spraying Rapid coating

Mechanical coating Ambient preparation

**2.1. Proposal of a novel coating technique** 

**Table 1.** Classification of the coating techniques for film materials

## **1.2. Advantages and limitations of these coating techniques**

Any film coating technique has its advantages and limitations. The features of these coating techniques make their application fields different. Their advantages and limitations are summarized and shown in Table 2. Thickness control and coating of large-area films can be achieved in PVD which has become the major film coating technique in the fields of electronics, electrics and optics industries due to its high production efficiency, high film purity and low production cost. However, complicated and large scale equipments are necessary. In addition, films cannot be deposit on the substrates with complex profiles. In CVD processes, films can deposit on the substrates with complex profiles and the adhesion between films and substrates is generally strong. However, the processes are performed at temperature of 600 ºC and above. Large scale equipments are also needed just as PVD processes. The advantages and limitations of other coating techniques can also be found in Table 2. We will not explain them in detail any more.


**Table 2.** Advantages and limitations of the film coating techniques

## **2. A novel coating technique for composite films**

## **2.1. Proposal of a novel coating technique**

324 Composites and Their Applications

Physical vapor deposition (PVD)

Chemical vapor deposition (CVD)

Liquid absorption coating

**Table 1.** Classification of the coating techniques for film materials

Vacuum deposition

Laser deposition

Sputter deposition

Ion beam deposition

Photo-excited CVD

Ionized cluster beam deposition

MBE (Molecular Beam Epitaxy )

heating

plasma deposition

Ion beam plating Highfrequency ion plating, Activated reactive evaporation, Arc ion plating

Thermal CVD Atmospheric pressure CVD, Low pressure CVD Plasma CVD DC plasma CVD, Highfrequency plasma CVD,

Resistance heating, Flash Evaporation, Vacuum Arc, Laser heating, Highfrequency heating, Electron beam

Ion beam sputtering, DC sputtering, Highfrequency sputtering, Magnetron sputtering, Microwave ECR

Microwave plasma CVD, ERC plasma CVD

Table 2. We will not explain them in detail any more.

**1.2. Advantages and limitations of these coating techniques** 

Thermal spraying Flame spraying, Electrical spraying ( Arc, Plasma )

Any film coating technique has its advantages and limitations. The features of these coating techniques make their application fields different. Their advantages and limitations are summarized and shown in Table 2. Thickness control and coating of large-area films can be achieved in PVD which has become the major film coating technique in the fields of electronics, electrics and optics industries due to its high production efficiency, high film purity and low production cost. However, complicated and large scale equipments are necessary. In addition, films cannot be deposit on the substrates with complex profiles. In CVD processes, films can deposit on the substrates with complex profiles and the adhesion between films and substrates is generally strong. However, the processes are performed at temperature of 600 ºC and above. Large scale equipments are also needed just as PVD processes. The advantages and limitations of other coating techniques can also be found in

Plating Electroplating, Electroless plating

Anodic oxide coating, Painting, Sol-gel method

Mechanical coating Shot coating, Powder impact plating, Aerosol deposition , Gas deposition

Spin coating, Dip coating, Roll coating, Spry coating

## *2.1.1. Contamination phenomena during Mechanical Alloying (MA)*

Powder metallurgy has been widely used in the manufacturing of mechanical parts. A typical process of powder metallurgy is shown in Fig. 1. As shown in the schematic diagram, blending of powder particles is necessary before compacting. Ball milling is often used to mix powder particles and make them homogeneous. Mechanical alloying, well known as ball milling, is frequently used to improve various material properties and to prepare advanced materials that are different or impossible to be obtained by traditional techniques (Suryanarayana, 2001). Ceramic balls are often used as grinding mediums which are indispensable in MA. However, the contamination of powder from grinding mediums and the adhesion of powder particles to the grinding mediums always harass engineers. Especially, the adhesion of powder particles to the grinding mediums and the bowl is really difficult to be eliminated.

## *2.1.2. Concept proposal of mechanical coating technique (MCT)*

From the contamination discussed above, we proposed a novel film coating technique in 2005 called mechanical coating technique (MCT) with the diagram schematic shown in Fig. 2 (Lu et al., 2005). In this technique, metal powder and ceramic grinding mediums (balls, buttons and columns) are used as the coating material and the substrates respectively. Firstly, they are charged into a bowl made of alumina. The mechanical coating is performed by a pot mill or a planetary ball mill. In the process, friction, wear and impact among metal powder particles, ceramic grinding mediums and the inner wall of the bowl occur. That results in the formation of metal films on ceramic grinding mediums. In fact, some other researchers prepared metal or alloy films on grinding mediums by this technique. Kobayashi prepared metallic films on ZrO2 balls (Kobayashi, 1995). Romankov et al. (2006) deposited Al and Ti-Al coatings on Ti alloy substrates. Gupta et al. (2009) reported the formation of nanocrystalline Fe-Si coatings on mild steel substrates. Farahbakhsh et al. (2011) prepared Cu and Ni-Cu solid solution coatings on Ni balls. Mechanical coating technique performed by ball milling has been established and known. After the proposal of MCT in 2005, we have made some important progress in advancing it. Titanium films on ceramic balls have been fabricated and their properties have been investigated (Yoshida et al., 2009 a). By MCT and its following high-temperature oxidation, TiO2/Ti composite photocatalyst films have been successfully prepared (H. Yoshida et al., 2008). After that, we proposed 2-step MCT to fabricate TiO2/Ti composite photocatalyst films without hightemperature oxidation (Lu et al., 2011). In addition, 2-step MCT was also used to fabricate TiO2/Cu composite photocatalyst films (Lu et al., 2012). In this chapter, we will give a brief introduction to MCT, 2-step MCT and the relevant processes as a novel technique to fabricate composite films and TiO2/metal composite photocatalyst films.

Mechanical Coating Technique for Composite Films and Composite Photocatalyst Films 327

Metal film-coated ceramic grinding mediums

Oxidized Ti films

(b) Alumina balls after MCT and the

Oxidized Fe-Al films

Pot mill

In our early work, we fabricated Ti films on alumina (Al2O3) grinding mediums such as balls, buttons and columns. Ti powder and Al2O3 grinding mediums were used as the coating materials and the substrates respectively. They were charged into a bowl made of alumina with the dimension of Φ75 × 90 mm (400 *ml*). The mechanical coating was carried out by a pot mill with a rotation speed of 80 rpm for 1000 h. Fig. 3 (a) shows the appearance comparison of the Al2O3 grinding mediums before and after MCT. It can be clearly seen that the Al2O3 grinding mediums after MCT showed metallic luster which means metal films might be formed on these grinding mediums. Also, the appearances of metal-coated Al2O3

> After MCT

following high-temperature oxidation (a) Alumina objects before and after MCT

**Figure 3.** Appearances of Al2O3 grinding mediums after MCT and high-temperature oxidation

Oxidized Ni-Al films

Planetary ball mill

Ceramic grinding mediums ( balls, columns and buttons )

**2.2. MCT and its influencing parameters** 

Before MCT

**Figure 2.** Schematic diagram of mechanical coating technique (MCT)

balls after high-temperature oxidation are given in Fig. 3 (b).

Metal powder

**Figure 1.** Simplified flowchart and schematic diagram of a typical powder metallurgy process

**Figure 2.** Schematic diagram of mechanical coating technique (MCT)

## **2.2. MCT and its influencing parameters**

326 Composites and Their Applications

researchers prepared metal or alloy films on grinding mediums by this technique. Kobayashi prepared metallic films on ZrO2 balls (Kobayashi, 1995). Romankov et al. (2006) deposited Al and Ti-Al coatings on Ti alloy substrates. Gupta et al. (2009) reported the formation of nanocrystalline Fe-Si coatings on mild steel substrates. Farahbakhsh et al. (2011) prepared Cu and Ni-Cu solid solution coatings on Ni balls. Mechanical coating technique performed by ball milling has been established and known. After the proposal of MCT in 2005, we have made some important progress in advancing it. Titanium films on ceramic balls have been fabricated and their properties have been investigated (Yoshida et al., 2009 a). By MCT and its following high-temperature oxidation, TiO2/Ti composite photocatalyst films have been successfully prepared (H. Yoshida et al., 2008). After that, we proposed 2-step MCT to fabricate TiO2/Ti composite photocatalyst films without hightemperature oxidation (Lu et al., 2011). In addition, 2-step MCT was also used to fabricate TiO2/Cu composite photocatalyst films (Lu et al., 2012). In this chapter, we will give a brief introduction to MCT, 2-step MCT and the relevant processes as a novel technique to

fabricate composite films and TiO2/metal composite photocatalyst films.

Metal or alloy powders

Blending

Mechanical alloying

Die compacting

Sintering

Optional secondary manufacturing

Re-pressing

Products

**Figure 1.** Simplified flowchart and schematic diagram of a typical powder metallurgy process

Inspection

In our early work, we fabricated Ti films on alumina (Al2O3) grinding mediums such as balls, buttons and columns. Ti powder and Al2O3 grinding mediums were used as the coating materials and the substrates respectively. They were charged into a bowl made of alumina with the dimension of Φ75 × 90 mm (400 *ml*). The mechanical coating was carried out by a pot mill with a rotation speed of 80 rpm for 1000 h. Fig. 3 (a) shows the appearance comparison of the Al2O3 grinding mediums before and after MCT. It can be clearly seen that the Al2O3 grinding mediums after MCT showed metallic luster which means metal films might be formed on these grinding mediums. Also, the appearances of metal-coated Al2O3 balls after high-temperature oxidation are given in Fig. 3 (b).

(b) Alumina balls after MCT and the following high-temperature oxidation (a) Alumina objects before and after MCT

The influencing parameters of MCT include:

1. Impact force or impact energy: type of mill, milling speed, milling container, milling time, grinding medium, extent of filling the bowl, ball-to-powder weight ratio

Mechanical Coating Technique for Composite Films and Composite Photocatalyst Films 329

(b) 600 h (c) 1000 h

(d) 4 h (e) 26 h

Al2O3ball(φ1mm)

0

Electrical resistance is one important property of film materials. Four-point probe method is frequently used to measure electrical resistance of films on a flat substrate (JIS K 7194, 1994).

(a) MCT with pot mill (b) MCT with planetary ball mill

5

10

15

MCT time / h

0 10 20 30

Al2O3 balls are shown in Fig. 6. Discrete Ti particles adhered to the surfaces of Al2O3 balls and they connected with each other. The irregular surface can result in high specific area. The thickness evolution of Ti films during MCT was also monitored and is illustrated in Fig. 7. No matter in the case of pot mill or planetary ball mill, the film thickness increased with the increase of MCT time. They reached 10 and 12 μm respectively in pot mill and planetary ball mill after 1000 h and 26 h. Therefore, it is possible to control the film thickness by MCT.

(a) before MCT

Al2O3ball(φ1mm)

Thickness / mm

0

5

10

15

**Figure 6.** Surface morphologies of Ti film-coated Al2O3 balls during MCT

MCT time / h

**Figure 7.** Thickness evolution of Ti films as a function of MCT time

0 200 400 600 800 1000

*2.3.2. Electrical resistance of the Ti films* 


## **2.3. Characterization of Ti films fabricated by MCT**

## *2.3.1. Appearance, microstructure and thickness of the Ti films*

Fig. 4 shows the appearances of the Al2O3 balls after MCT. It can be seen that the color of the Al2O3 balls changed from white to metallic gray as MCT time increased. It means that more Ti powder particles adhered to the surfaces of the Al2O3 balls. Impact force of only about 1 G can be obtained during MCT performed by pot mill. When it is carried out by planetary ball mill, impact force over 10 G or even 40 G can be realized. Therefore, the required time to form metal films can be decreased greatly in the case of planetary ball mill. The SEM images of the cross sections of the Ti-coated Al2O3 balls are also given in Fig. 5. With the increase of MCT time, the film thickness increased. The surface morphologies of the Ti film-coated

**Figure 4.** Appearances of the Ti-coated Al2O3 balls during MCT for different MCT time

**Figure 5.** SEM images of the cross sections of the Ti film-coated Al2O3 balls during MCT

Al2O3 balls are shown in Fig. 6. Discrete Ti particles adhered to the surfaces of Al2O3 balls and they connected with each other. The irregular surface can result in high specific area. The thickness evolution of Ti films during MCT was also monitored and is illustrated in Fig. 7. No matter in the case of pot mill or planetary ball mill, the film thickness increased with the increase of MCT time. They reached 10 and 12 μm respectively in pot mill and planetary ball mill after 1000 h and 26 h. Therefore, it is possible to control the film thickness by MCT.

**Figure 6.** Surface morphologies of Ti film-coated Al2O3 balls during MCT

**Figure 7.** Thickness evolution of Ti films as a function of MCT time

## *2.3.2. Electrical resistance of the Ti films*

328 Composites and Their Applications

The influencing parameters of MCT include:

3. Milling atmosphere and milling temperature

**2.3. Characterization of Ti films fabricated by MCT** 

0 h 100 h 300 h 500 h 1000 h (a) MCT with pot mill

(a) before MCT

**Figure 4.** Appearances of the Ti-coated Al2O3 balls during MCT for different MCT time

**Al2O3**

**Al2O3**

**Figure 5.** SEM images of the cross sections of the Ti film-coated Al2O3 balls during MCT

*2.3.1. Appearance, microstructure and thickness of the Ti films* 

1. Impact force or impact energy: type of mill, milling speed, milling container, milling time, grinding medium, extent of filling the bowl, ball-to-powder weight ratio 2. Physic, chemical and mechanical properties of powder and grinding mediums

Fig. 4 shows the appearances of the Al2O3 balls after MCT. It can be seen that the color of the Al2O3 balls changed from white to metallic gray as MCT time increased. It means that more Ti powder particles adhered to the surfaces of the Al2O3 balls. Impact force of only about 1 G can be obtained during MCT performed by pot mill. When it is carried out by planetary ball mill, impact force over 10 G or even 40 G can be realized. Therefore, the required time to form metal films can be decreased greatly in the case of planetary ball mill. The SEM images of the cross sections of the Ti-coated Al2O3 balls are also given in Fig. 5. With the increase of MCT time, the film thickness increased. The surface morphologies of the Ti film-coated

> 0 h 10 h 26 h (b) MCT with planetary ball mill

> > **Ti film**

(b) 400 h (c) 1000 h

**Al2O3 Ti film**

**Al2O3**

**Al2O3 Ti film**

**Ti film**

(d) 4 h (e) 26 h

Electrical resistance is one important property of film materials. Four-point probe method is frequently used to measure electrical resistance of films on a flat substrate (JIS K 7194, 1994). However, this method is only applicable to planar films. It cannot used to measure the electrical resistance of spherical films. Therefore, we proposed a new electrical resistance determination method of spherical films such as Ti films on Al2O3 balls. By this method, we established the relationship between electrical resistivity and film thickness.

Mechanical Coating Technique for Composite Films and Composite Photocatalyst Films 331

(1)

r r dz dz <sup>ρ</sup> R = <sup>ρ</sup> <sup>=</sup> <sup>1</sup> 0 0 A 22 <sup>π</sup> <sup>1</sup> (r+h) -r (2)

r+h r+h dz <sup>ρ</sup> dz R = <sup>ρ</sup> <sup>=</sup> <sup>2</sup> r r <sup>A</sup> <sup>π</sup> 2 2 <sup>2</sup> (r+h) -z (3)

(4)

(5)

Al2O3 ball, *h* is the film thickness. Therefore, the electrical resistance of the spherical Ti films

Where *ρ* is the electrical resistivity of the films, *A*1 is the ring area of the films in the range of 0 ≤ *z* ≤ *r*, and *A*2 is the area of the circle crossed with vertical axis *z* in the range of *r* < *z* ≤ *r+h*. Electrical resistance in the range of 0 ≤ *z* ≤ *r* and *r* < *z* ≤ *r+h* can be defined as *R*1 and *R*<sup>2</sup>

During the measurement of electrical resistance shown in Fig. 8, the contact of the plate probes and Al2O3 ball should not be a point but a plane which has a certain area. It is proper

2 2 <sup>C</sup> ρ ρ dz (r+h) -C R = = ln <sup>2</sup> <sup>r</sup> <sup>π</sup> <sup>2</sup> <sup>2</sup>π(r+h) 2 2 <sup>2</sup> (r+h) -r r+h -C

2 2 ρ ρ <sup>r</sup> (r+h) -C R = 2(R + R ) = 2 + ln 1 2 <sup>π</sup> 2 2 <sup>2</sup>π(r+h) 2 2 (r+h) -r (r+h) -r

The electrical resistance of the spherical Ti films on an Al2O3 ball can be given by

**Figure 10.** Spherical shell model for the electrical resistance of the Ti film-coated Al2O3 balls

on Al2O3 ball *z* = +(*r*+*h*) to *z* = -(*r*+*h*) can be given by

to give the integral calculus from *r* to *C* (*r* < *C* ≤ *r+h*).

respectively and can be given by

+(r+h) +(r+h) dz dz dz R = <sup>ρ</sup> =2 (<sup>ρ</sup> <sup>+</sup> <sup>ρ</sup> ) -(r+h) A AA <sup>0</sup> 1 2

The determination method is shown in Fig. 8. Two plate probes contacts the Ti film-coated Al2O3 ball (Φ 1 mm) along the direction of tangential line. To decrease contact resistance, a pressure force of 800 gf is loaded along the normal direction of the ball. The press force is determined in pre-experiments. Electrical resistance is measured for 10 times by changing the contact points between the two plate probes and the ball. In addition, the measurement on electrical resistance is carried out for three randomly chosen Ti film-coated Al2O3 balls. The average value of the measurements for 30 times is used as the electrical resistance of the Ti film. Fig. 9 shows the evolution of electrical resistance of the Ti film-coated Al2O3 balls during MCT by pot mill and planetary ball mill. For the both cases, the electrical resistance decreased with the increase of MCT time.

**Figure 8.** Measurement of electrical resistance of the Ti film-coated Al2O3 balls

**Figure 9.** Electrical resistance of the Ti film-coated Al2O3 balls

To establish the relationship between electrical resistance and film thickness, we proposed a spherical shell model for Ti film-coated Al2O3 ball as shown in Fig. 10. Here *r* is the radius of Al2O3 ball, *h* is the film thickness. Therefore, the electrical resistance of the spherical Ti films on Al2O3 ball *z* = +(*r*+*h*) to *z* = -(*r*+*h*) can be given by

330 Composites and Their Applications

decreased with the increase of MCT time.

<sup>200</sup> <sup>400</sup> <sup>600</sup> 800 1000 <sup>0</sup>

MCT time / h

**Figure 9.** Electrical resistance of the Ti film-coated Al2O3 balls

50

Electrical resistance /

Ω

100

150

However, this method is only applicable to planar films. It cannot used to measure the electrical resistance of spherical films. Therefore, we proposed a new electrical resistance determination method of spherical films such as Ti films on Al2O3 balls. By this method, we

The determination method is shown in Fig. 8. Two plate probes contacts the Ti film-coated Al2O3 ball (Φ 1 mm) along the direction of tangential line. To decrease contact resistance, a pressure force of 800 gf is loaded along the normal direction of the ball. The press force is determined in pre-experiments. Electrical resistance is measured for 10 times by changing the contact points between the two plate probes and the ball. In addition, the measurement on electrical resistance is carried out for three randomly chosen Ti film-coated Al2O3 balls. The average value of the measurements for 30 times is used as the electrical resistance of the Ti film. Fig. 9 shows the evolution of electrical resistance of the Ti film-coated Al2O3 balls during MCT by pot mill and planetary ball mill. For the both cases, the electrical resistance

established the relationship between electrical resistivity and film thickness.

**Figure 8.** Measurement of electrical resistance of the Ti film-coated Al2O3 balls

0

To establish the relationship between electrical resistance and film thickness, we proposed a spherical shell model for Ti film-coated Al2O3 ball as shown in Fig. 10. Here *r* is the radius of

(a) MCT with pot mill (b) MCT with planetary ball mill

10

20

0 10 20 30

MCT time / h

$$\mathbf{R} = \mathbf{\hat{f}}^{+(\mathbf{r}+\mathbf{h})}\_{\mathbf{(r}+\mathbf{h})} \boldsymbol{\rho} \frac{\mathbf{dx}}{\mathbf{A}} = 2\mathbf{\hat{f}}^{+(\mathbf{r}+\mathbf{h})}\_{\mathbf{0}} (\mathbf{p}\frac{\mathbf{dx}}{\mathbf{A}\_{\mathbf{l}}} + \boldsymbol{\rho}\frac{\mathbf{dx}}{\mathbf{A}\_{\mathbf{2}}}) \tag{1}$$

Where *ρ* is the electrical resistivity of the films, *A*1 is the ring area of the films in the range of 0 ≤ *z* ≤ *r*, and *A*2 is the area of the circle crossed with vertical axis *z* in the range of *r* < *z* ≤ *r+h*. Electrical resistance in the range of 0 ≤ *z* ≤ *r* and *r* < *z* ≤ *r+h* can be defined as *R*1 and *R*<sup>2</sup> respectively and can be given by

$$\mathbf{R}\_{\rm I} = \mathbf{j\_0^I} \rho \frac{\mathbf{dz}}{\mathbf{A\_{\rm I}}} = \mathbf{j\_0^I} \frac{\mathbf{p}}{\pi} \frac{\mathbf{dz}}{(\mathbf{r} + \mathbf{h})^2 \mathbf{-r}^2} \tag{2}$$

$$\mathbf{R}\_2 = \mathfrak{l}\_\mathbf{r}^{\mathbf{r}+\mathbf{h}} \rho \frac{\mathrm{d}\mathbf{z}}{\mathrm{A}\_2} = \mathfrak{l}\_\mathbf{r}^{\mathbf{r}+\mathbf{h}} \frac{\mathfrak{p}}{\mathfrak{a}} \frac{\mathrm{d}\mathbf{z}}{(\mathfrak{r}+\mathbf{h})^2 \cdot \mathbf{z}^2} \tag{3}$$

During the measurement of electrical resistance shown in Fig. 8, the contact of the plate probes and Al2O3 ball should not be a point but a plane which has a certain area. It is proper to give the integral calculus from *r* to *C* (*r* < *C* ≤ *r+h*).

$$\mathbf{R}\_2 = \text{f}\_\mathbf{r}^\mathbf{C} \frac{\mathbf{p}}{\pi} \frac{\text{d}\mathbf{z}}{\text{(r+h)}^2 \text{-}\text{C}^2} = \frac{\rho}{2\pi (\text{r} + \text{h})} \ln \left| \frac{(\text{r} + \text{h})^2 \text{-}\text{C}^2}{(\text{r} + \text{h})^2 \text{-}\text{r}^2} \right| \tag{4}$$

The electrical resistance of the spherical Ti films on an Al2O3 ball can be given by

$$\mathbf{R} = 2(\mathbf{R}\_1 + \mathbf{R}\_2) = 2 \left| \frac{\rho}{\pi} \frac{\mathbf{r}}{(\mathbf{r} + \mathbf{h})^2 \mathbf{-} \mathbf{r}^2} + \frac{\rho}{2\pi (\mathbf{r} + \mathbf{h})} \ln \left| \frac{(\mathbf{r} + \mathbf{h})^2 \mathbf{-} \mathbf{C}^2}{(\mathbf{r} + \mathbf{h})^2 \mathbf{-} \mathbf{r}^2} \right| \right| \tag{5}$$

**Figure 10.** Spherical shell model for the electrical resistance of the Ti film-coated Al2O3 balls

Therefore, we can calculate electrical resistivity, *ρ* of the film by Eq. 5 using the measured electrical resistance of the films, *R* and the film thickness, *h*. Fig. 11 shows the relationship between the electrical resistivity of the Ti films and their thickness. It can be found that the electrical resistivity went down and then kept a constant. The evolution of the electrical resistivity should result from the density evolution of the films. In the case of planetary ball mill, the stable electrical resistivity was smaller than that in the case of pot mill. That should be due to the higher film density obtained in the circumstance of larger impact force in the case of planetary ball mill.

Mechanical Coating Technique for Composite Films and Composite Photocatalyst Films 333

1mm

samples were oxidized in air at 573, 623, 673, 723, 773, 873 and 973 K for 20 h. Here the samples were denoted as M10-*T*-20. *T* means the oxidation temperature. The samples after MCT and the following high-temperature oxidation were examined by SEM (JEOL, JSM-6100) and XRD (JEOL, JDX-3530). Cu-*Kα* radiation in the condition of 30 kV and 30 mA was used for XRD. Before the characterization, all the samples were cleaned in acetone by

Fig. 12 shows the appearances of the M10-Ti and M10-*T*-20 samples. The color of the M10-*T*-20 samples changed with increase of oxidation temperature and lost metallic luster comparing with M10-Ti. The color change indicates that the degree of oxidation was different at different oxidation temperature. The M10-573-20 samples showed brown color which was similar to that of TiO. That means the oxidation of Ti films at 573 K was insufficient. When oxidation temperature was increased to 673, 723, 773 and 873 K, the samples color changed from blue to gray. It was probably related to the growth of TiO2 crystalline and the film thickness increase. Besides, the color of M10-973-20 samples was

ultrasonic (frequency: 28 kHz) to remove Ti and TiO2 that did not adhere strongly.

light yellow. It indicates that titanium was completely oxidized to titanium dioxide.

(a) M10-Ti (b) 573 K (c) 623 K (d) 673 K

(e) 723 K (f) 773 K (g) 873 K (g) 973 K

The surface SEM images of the samples are shown in Fig. 13. From Fig. 13(a), the Ti films had uneven surfaces comparing with those prepared by PVD or CVD. The surface evolution with the increase of oxidation temperature can be seen from Fig. 13(b) to (f). It seems that the surface crystals grew up with the increase of oxidation temperature. However, column nanocrystals were formed at 973 K. Fig. 14 shows the XRD patterns of the samples after MCT and the following high-temperature oxidation. The diffraction intensity of Ti peaks decreased with the increase of oxidation temperature and the Ti peak at about 41° (2θ) disappeared when oxidation temperature was increased to 973 K. Conversely, the peaks of rutile TiO2 appeared when oxidation temperature was above 673 K and the diffraction intensity became stronger as oxidation temperature increased. From the above results, it can be concluded that the films had a composite microstructure of Ti and rutile TiO2 when oxidation temperature was between 673 and 873 K. TiO2/Ti composite films on Al2O3 balls

were fabricated by MCT and the following high-temperature oxidation.

*2.4.2. Characterization of the TiO2/Ti composite films* 

**Figure 12.** Appearances of M10-Ti and M10-*T*-20 samples

**Figure 11.** Relationship between electrical resistivity of Ti films and their thicknesses

## **2.4. TiO2/Ti composite films fabricated by MCT and the following high-temperature oxidation**

We successfully fabricated TiO2/Ti composite films by MCT and the following hightemperature oxidation. Firstly, Ti films were prepared by MCT shown in Fig. 2. Subsequently, the Ti film-coated Al2O3 balls were oxidized at high temperatures. In this section, we will introduce the fabricate processes and the characterization of the TiO2/Ti composite films.

#### *2.4.1. Fabrication processes*

Ti powder with a purity of 99.9% and an average diameter of 30 μm was used as the coating material. Al2O3 balls with an average diameter of 1 mm were used as the substrates. A planetary ball mill (P5/4, Fritsch) was used to perform MCT (Yoshida, 2009 b). 40 g Ti powder and 60 g Al2O3 balls were charged into a bowl made of alumina with a dimension of Φ75×70 mm (250 *ml*). MCT was carried out with a rotation speed of 300 rpm for 10 h. The obtained Ti film-coated Al2O3 balls were denoted as M10-Ti. To form TiO2 films, the M10-Ti samples were oxidized in air at 573, 623, 673, 723, 773, 873 and 973 K for 20 h. Here the samples were denoted as M10-*T*-20. *T* means the oxidation temperature. The samples after MCT and the following high-temperature oxidation were examined by SEM (JEOL, JSM-6100) and XRD (JEOL, JDX-3530). Cu-*Kα* radiation in the condition of 30 kV and 30 mA was used for XRD. Before the characterization, all the samples were cleaned in acetone by ultrasonic (frequency: 28 kHz) to remove Ti and TiO2 that did not adhere strongly.

## *2.4.2. Characterization of the TiO2/Ti composite films*

332 Composites and Their Applications

case of planetary ball mill.

0

0.1

Electrical resistivity /

**high-temperature oxidation** 

*2.4.1. Fabrication processes* 

composite films.

Ωmm

0.2

0.3

Therefore, we can calculate electrical resistivity, *ρ* of the film by Eq. 5 using the measured electrical resistance of the films, *R* and the film thickness, *h*. Fig. 11 shows the relationship between the electrical resistivity of the Ti films and their thickness. It can be found that the electrical resistivity went down and then kept a constant. The evolution of the electrical resistivity should result from the density evolution of the films. In the case of planetary ball mill, the stable electrical resistivity was smaller than that in the case of pot mill. That should be due to the higher film density obtained in the circumstance of larger impact force in the

0 5 10

We successfully fabricated TiO2/Ti composite films by MCT and the following hightemperature oxidation. Firstly, Ti films were prepared by MCT shown in Fig. 2. Subsequently, the Ti film-coated Al2O3 balls were oxidized at high temperatures. In this section, we will introduce the fabricate processes and the characterization of the TiO2/Ti

Ti powder with a purity of 99.9% and an average diameter of 30 μm was used as the coating material. Al2O3 balls with an average diameter of 1 mm were used as the substrates. A planetary ball mill (P5/4, Fritsch) was used to perform MCT (Yoshida, 2009 b). 40 g Ti powder and 60 g Al2O3 balls were charged into a bowl made of alumina with a dimension of Φ75×70 mm (250 *ml*). MCT was carried out with a rotation speed of 300 rpm for 10 h. The obtained Ti film-coated Al2O3 balls were denoted as M10-Ti. To form TiO2 films, the M10-Ti

**Figure 11.** Relationship between electrical resistivity of Ti films and their thicknesses

**2.4. TiO2/Ti composite films fabricated by MCT and the following** 

Thickness / μm

MCT with planetary ball mill

MCT with pot mill

Fig. 12 shows the appearances of the M10-Ti and M10-*T*-20 samples. The color of the M10-*T*-20 samples changed with increase of oxidation temperature and lost metallic luster comparing with M10-Ti. The color change indicates that the degree of oxidation was different at different oxidation temperature. The M10-573-20 samples showed brown color which was similar to that of TiO. That means the oxidation of Ti films at 573 K was insufficient. When oxidation temperature was increased to 673, 723, 773 and 873 K, the samples color changed from blue to gray. It was probably related to the growth of TiO2 crystalline and the film thickness increase. Besides, the color of M10-973-20 samples was light yellow. It indicates that titanium was completely oxidized to titanium dioxide.

**Figure 12.** Appearances of M10-Ti and M10-*T*-20 samples

The surface SEM images of the samples are shown in Fig. 13. From Fig. 13(a), the Ti films had uneven surfaces comparing with those prepared by PVD or CVD. The surface evolution with the increase of oxidation temperature can be seen from Fig. 13(b) to (f). It seems that the surface crystals grew up with the increase of oxidation temperature. However, column nanocrystals were formed at 973 K. Fig. 14 shows the XRD patterns of the samples after MCT and the following high-temperature oxidation. The diffraction intensity of Ti peaks decreased with the increase of oxidation temperature and the Ti peak at about 41° (2θ) disappeared when oxidation temperature was increased to 973 K. Conversely, the peaks of rutile TiO2 appeared when oxidation temperature was above 673 K and the diffraction intensity became stronger as oxidation temperature increased. From the above results, it can be concluded that the films had a composite microstructure of Ti and rutile TiO2 when oxidation temperature was between 673 and 873 K. TiO2/Ti composite films on Al2O3 balls were fabricated by MCT and the following high-temperature oxidation.

(d) M10-773-20 (e) M10-873-20 (f) M10-973-20

Mechanical Coating Technique for Composite Films and Composite Photocatalyst Films 335

M10-Ti (Ti films)

**+**

TiO2-S or TiO2-K

**+** Al2O3 or WC impact balls

Al2O3 pot

The schematic diagram of 2-step MCT is shown in Fig. 15. In the first step, Ti films are prepared on the surfaces of Al2O3 balls as our previous work (Lu et al., 2005 & Yoshida et al., 2009 a). The source materials and their relevant parameters are listed in Table 3. 40 g Ti powder and 60 g Al2O3 balls are used as the coating material and the substrates respectively. A planetary ball mill (P5/4, Fritsch) is used to perform MCT. The experimental condition has been discussed in Section 2.4.1. In the second step, TiO2/Ti composite films are fabricated. 15 g Ti film-coated Al2O3 balls and 13 g TiO2 powder are used as the substrates and the coating material respectively. The relevant parameters can be found in Table 3. They are charged into a bowl made of alumina. Then the coating of TiO2 is performed by the same planetary ball mill with a rotation speed of 300 rpm for 1, 3, 6 and 10 h. To investigate the influence of average diameter of TiO2 powder on the photocatalytic activity of the composite films, two kinds of anatase TiO2 powder with different average diameter are used as the coating materials. To understand the influence of impact force on the formation and the photocatalytic activity of TiO2/Ti composite films, Al2O3 or WC impact balls with the diameter of 10 mm are also introduced into the second step of 2-step MCT. The relevant

*2.5.1. Processes of 2-step MCT* 

denotations are listed in Table 4.

**1-step: forming Ti films**

Al2O3 pot

**2-step: forming TiO2/Ti films**

Al2O3 balls Planetary ball mill

Planetary ball mill

**Figure 15.** Schematic diagram of 2-step MCT for the fabrication of TiO2/Ti composite films

**Figure 13.** Surface SEM images of M10-Ti and M10-*T*-20 samples

**Figure 14.** XRD patterns of M10-Ti and M10-T-20 samples

## **2.5. 2-step Mechanical Coating Technique (2-step MCT)**

An advanced mechanical coating technique called 2-step mechanical coating technique (2 step MCT) was developed to fabricate TiO2/Ti composite films. As anatase TiO2 cannot be easily obtained by oxidation, we aim to deposit anatase TiO2 on Ti films directly by MCT. In this section, we will introduce the processes of 2-step MCT and characterize the composite films. The influences of 2nd step MCT time and the introduction of ceramic impact balls on the composite films and their photocatalytic activity were also discussed.

### *2.5.1. Processes of 2-step MCT*

334 Composites and Their Applications

(a) M10-Ti

Diffraction intensity / a. u.

**Figure 13.** Surface SEM images of M10-Ti and M10-*T*-20 samples

Al2O3 TiO2 (rutile )

Ti

**Figure 14.** XRD patterns of M10-Ti and M10-T-20 samples

**2.5. 2-step Mechanical Coating Technique (2-step MCT)** 

the composite films and their photocatalytic activity were also discussed.

(b) M10-573-20 (c) M10-673-20

**1μm**

(d) M10-773-20 (e) M10-873-20 (f) M10-973-20

30 40 50 2θ / deg

An advanced mechanical coating technique called 2-step mechanical coating technique (2 step MCT) was developed to fabricate TiO2/Ti composite films. As anatase TiO2 cannot be easily obtained by oxidation, we aim to deposit anatase TiO2 on Ti films directly by MCT. In this section, we will introduce the processes of 2-step MCT and characterize the composite films. The influences of 2nd step MCT time and the introduction of ceramic impact balls on

M10-Ti 573 K

673 K 623 K

723 K 773 K 873 K 973 K The schematic diagram of 2-step MCT is shown in Fig. 15. In the first step, Ti films are prepared on the surfaces of Al2O3 balls as our previous work (Lu et al., 2005 & Yoshida et al., 2009 a). The source materials and their relevant parameters are listed in Table 3. 40 g Ti powder and 60 g Al2O3 balls are used as the coating material and the substrates respectively. A planetary ball mill (P5/4, Fritsch) is used to perform MCT. The experimental condition has been discussed in Section 2.4.1. In the second step, TiO2/Ti composite films are fabricated. 15 g Ti film-coated Al2O3 balls and 13 g TiO2 powder are used as the substrates and the coating material respectively. The relevant parameters can be found in Table 3. They are charged into a bowl made of alumina. Then the coating of TiO2 is performed by the same planetary ball mill with a rotation speed of 300 rpm for 1, 3, 6 and 10 h. To investigate the influence of average diameter of TiO2 powder on the photocatalytic activity of the composite films, two kinds of anatase TiO2 powder with different average diameter are used as the coating materials. To understand the influence of impact force on the formation and the photocatalytic activity of TiO2/Ti composite films, Al2O3 or WC impact balls with the diameter of 10 mm are also introduced into the second step of 2-step MCT. The relevant denotations are listed in Table 4.

**Figure 15.** Schematic diagram of 2-step MCT for the fabrication of TiO2/Ti composite films


Mechanical Coating Technique for Composite Films and Composite Photocatalyst Films 337

1mm

100μm

reached their highest values. It indicates that the loading amounts of TiO2 in the TiO2/Ti composite films reached the maximum values. After that, the TiO2 peaks became lower which should be due to the exfoliation of TiO2 that coated Ti films. From the above results, the films had a composite microstructure of Ti and TiO2. The loading amounts of TiO2 in the composite films changed with the increase of the 2nd step MCT time. 2-step MCT is a simple

M10-Ti CM1S CM3S CM6S CM10S

(a) M10-Ti (b) CM3S (c) CM10S

**Ti**

**Figure 18.** SEM images of the cross sections of the samples fabricated by 2-step MCT

*2.5.3. TiO2/Ti composite films fabricated by 2-step MCT with impact balls* 

**Al2O3 Al Al2O3 2O3**

(a) CM1S (b) CM3S (c) CM6S

Fig. 20 shows the appearances of the Al2O3 balls after 2-step MCT with ceramic impact balls. The samples lost metallic luster and their colors changed. That hints TiO2/Ti composite films might be formed. Fig. 21 shows the SEM image of the cross section of the TiO2/Ti composite

**TiO2**

**Al2O3 Al2O3**

**Ti**

300mm

**TiO2**

10μm

**Figure 17.** SEM images of the surfaces of the samples fabricated by 2-step MCT

and applicable technique to fabricate TiO2/Ti composite films.

**Figure 16.** Appearances of the samples after 2-step MCT

**Al2O3**

**TiO2**

**Ti**


Note: *x* is the 2nd step MCT time.

**Table 4.** Sample denotations for the fabrication of TiO2/Ti composite films by 2-step MCT

#### *2.5.2. TiO2/Ti composite films fabricated by 2-step MCT without impact balls*

Fig. 16 shows the appearances of the Al2O3 balls after 2-step MCT without ceramic impact balls. The color of the samples changed and lost metallic luster with the increase of the 2nd step MCT time. The CM3S samples showed different colors from place to place on the surface. However, the CM6S and CM10S samples showed uniform color respectively. It hints that uniform composite films might form at that time. Fig. 17 shows the surface SEM images of the samples fabricated by 2-step MCT without ceramic impact balls. From Fig. 17(a), the gray areas correspond to Ti. It can be seen that uniform Ti films have been formed on the surface of Al2O3 ball. From Fig. 17(b) and (c), the white and gray areas correspond to Ti and TiO2 respectively. Continuous TiO2 films were not form while TiO2 deposited on Ti films in the form of discrete island. Meanwhile, the SEM images of the cross sections of the samples fabricated by 2-step MCT without ceramic impact balls are shown in Fig. 18. It can be clearly seen that Al2O3 balls were coated with Ti films and discrete islands of TiO2 adhered to the Ti films. A composite microstructure of Ti and TiO2 was formed. During the impact between Al2O3 balls or Al2O3 ball and the inner wall of the bowl, TiO2 powder particles were trapped between them. Under the great impact force, TiO2 particles were inlaid into the Ti films. It results in the formation of the TiO2/Ti composite microstructure. Fig. 19 shows the XRD patterns of the samples after 2-step MCT without impact balls. When the 2nd step MCT time was 1 h, the peaks of anatase TiO2 appeared which means that TiO2 particles had adhered to Ti films. As it came to 3 h, the intensity of anatase TiO2 peaks reached their highest values. It indicates that the loading amounts of TiO2 in the TiO2/Ti composite films reached the maximum values. After that, the TiO2 peaks became lower which should be due to the exfoliation of TiO2 that coated Ti films. From the above results, the films had a composite microstructure of Ti and TiO2. The loading amounts of TiO2 in the composite films changed with the increase of the 2nd step MCT time. 2-step MCT is a simple and applicable technique to fabricate TiO2/Ti composite films.

**Figure 16.** Appearances of the samples after 2-step MCT

336 Composites and Their Applications

Ti powder Purity: 99.1%

Substrate <sup>ϕ</sup>1 Al2O3 balls

TiO2 powder (anatase)

TiO2

TiO2-S

TiO2-K

Note: *x* is the 2nd step MCT time.

**Table 4.** Sample denotations for the fabrication of TiO2/Ti composite films by 2-step MCT

*2.5.2. TiO2/Ti composite films fabricated by 2-step MCT without impact balls* 

Fig. 16 shows the appearances of the Al2O3 balls after 2-step MCT without ceramic impact balls. The color of the samples changed and lost metallic luster with the increase of the 2nd step MCT time. The CM3S samples showed different colors from place to place on the surface. However, the CM6S and CM10S samples showed uniform color respectively. It hints that uniform composite films might form at that time. Fig. 17 shows the surface SEM images of the samples fabricated by 2-step MCT without ceramic impact balls. From Fig. 17(a), the gray areas correspond to Ti. It can be seen that uniform Ti films have been formed on the surface of Al2O3 ball. From Fig. 17(b) and (c), the white and gray areas correspond to Ti and TiO2 respectively. Continuous TiO2 films were not form while TiO2 deposited on Ti films in the form of discrete island. Meanwhile, the SEM images of the cross sections of the samples fabricated by 2-step MCT without ceramic impact balls are shown in Fig. 18. It can be clearly seen that Al2O3 balls were coated with Ti films and discrete islands of TiO2 adhered to the Ti films. A composite microstructure of Ti and TiO2 was formed. During the impact between Al2O3 balls or Al2O3 ball and the inner wall of the bowl, TiO2 powder particles were trapped between them. Under the great impact force, TiO2 particles were inlaid into the Ti films. It results in the formation of the TiO2/Ti composite microstructure. Fig. 19 shows the XRD patterns of the samples after 2-step MCT without impact balls. When the 2nd step MCT time was 1 h, the peaks of anatase TiO2 appeared which means that TiO2 particles had adhered to Ti films. As it came to 3 h, the intensity of anatase TiO2 peaks

Average diameter: 30 μm

powder Impact ball Sample denotation

Average diameter: 7 nm (TiO2-S)

Average diameter: 0.45 μm (TiO2-K)

Al2O3 ϕ10A-CM*x*S WC ϕ10W-CM*x*S

Al2O3 ϕ10A-CM*x*K WC ϕ10W-CM*x*K

CM*x*S

CM*x*K

Purity: 93.0%

**Table 3.** Source materials for the fabrication of TiO2/Ti composite films by 2-step MCT

**Figure 17.** SEM images of the surfaces of the samples fabricated by 2-step MCT

**Figure 18.** SEM images of the cross sections of the samples fabricated by 2-step MCT

## *2.5.3. TiO2/Ti composite films fabricated by 2-step MCT with impact balls*

Fig. 20 shows the appearances of the Al2O3 balls after 2-step MCT with ceramic impact balls. The samples lost metallic luster and their colors changed. That hints TiO2/Ti composite films might be formed. Fig. 21 shows the SEM image of the cross section of the TiO2/Ti composite films fabricated by 2-step MCT with WC impact balls. It can be seen that the films had a composite microstructure of Ti film and discrete islands of TiO2. The surface condition of the composite films fabricated with TiO2 powder with different average diameters are compared in Fig. 22. The distribution of TiO2 powder particles with the average diameter of 0.45 μm were more uneven under the impact of WC balls compared with those with the average diameter of 7 nm. Φ10W-CM6K sample had a high hardness of 472 (dynamic hardness) on the cross section. It was close to that of alumina. It hints that the composite films were very hard.

Mechanical Coating Technique for Composite Films and Composite Photocatalyst Films 339

ϕ10W-CM10K

ϕ10W-CM6K

ϕ10W-CM3K

ϕ10W-CM1K

M10-Ti

30 40 50

2θ / deg (b) TiO2 powder with the average diameter of 0.45 μm

(a) ϕ10W-CM6S (b) ϕ10W-CM6K

The XRD patterns of the samples fabricated with TiO2 powder of different average diameters by 2-step MCT with WC impact balls are given in Fig. 23. In the case of nanosized TiO2 powder (Fig.23 (a)), the peaks of Ti and TiO2 can be found. On the other hand, the diffraction peaks of TiO2 cannot be detected for the micron-sized TiO2 powder (Fig.23 (b)). It

**100μm**

100μm

**Figure 22.** Surface SEM images of the samples fabricated by 2-step MCT

30 40 50

**Figure 23.** XRD patterns of the samples fabricated by 2-step MCT with WC impact balls

Although the photocatalytic activity of TiO2 under ultraviolet and visible light irradiation has been investigated around the world, only the photocatalytic activity of TiO2/metal composite films under ultraviolet irradiation is involved and discussed in this section. Here, we developed evaluation method of photocatalytic activity of TiO2/metal composite films by which we evaluated the photocatalytic activity of TiO2/Ti and TiO2/Cu composite films

**3. Photocatalytic activity of TiO2/metal composite films** 

2θ / deg

(a) TiO2 powder with the average diameter of 7 nm

Diffraction intensity / a. u.

Ti

Al2O3 TiO2 (anatase)

ϕ10W-CM10S

ϕ10W-CM6S

ϕ10W-CM3S

ϕ10W-CM1S

M10-Ti

fabricated by MCT.

means the loading amounts of TiO2 in the composite films were rather small.

**Figure 19.** XRD patterns of the samples fabricated by 2-step MCT

**Figure 20.** Appearances of the samples fabricated by 2-step MCT

**Figure 21.** SEM image of the cross section of the Φ10W-CM6K sample fabricated by 2-step MCT

Mechanical Coating Technique for Composite Films and Composite Photocatalyst Films 339

**Figure 22.** Surface SEM images of the samples fabricated by 2-step MCT

338 Composites and Their Applications

films were very hard.

films fabricated by 2-step MCT with WC impact balls. It can be seen that the films had a composite microstructure of Ti film and discrete islands of TiO2. The surface condition of the composite films fabricated with TiO2 powder with different average diameters are compared in Fig. 22. The distribution of TiO2 powder particles with the average diameter of 0.45 μm were more uneven under the impact of WC balls compared with those with the average diameter of 7 nm. Φ10W-CM6K sample had a high hardness of 472 (dynamic hardness) on the cross section. It was close to that of alumina. It hints that the composite

> M10-Ti ST-01

> > 30 40 50 2θ / deg

M10-Ti CM6S ϕ10A-CM6S ϕ10W-CM6S

CM6K <sup>ϕ</sup>10A-CM6K <sup>ϕ</sup>10W-CM6K 1mm

Al2O3 ball Ti

**Figure 21.** SEM image of the cross section of the Φ10W-CM6K sample fabricated by 2-step MCT

TiO2

CM1S CM3S

CM6S

Diffraction intensity / a. u.

23

**Figure 19.** XRD patterns of the samples fabricated by 2-step MCT

**Figure 20.** Appearances of the samples fabricated by 2-step MCT

CM10S

Ti Al2O3 TiO2 (anatase)

The XRD patterns of the samples fabricated with TiO2 powder of different average diameters by 2-step MCT with WC impact balls are given in Fig. 23. In the case of nanosized TiO2 powder (Fig.23 (a)), the peaks of Ti and TiO2 can be found. On the other hand, the diffraction peaks of TiO2 cannot be detected for the micron-sized TiO2 powder (Fig.23 (b)). It means the loading amounts of TiO2 in the composite films were rather small.

(a) TiO2 powder with the average diameter of 7 nm (b) TiO2 powder with the average diameter of 0.45 μm

#### **Figure 23.** XRD patterns of the samples fabricated by 2-step MCT with WC impact balls

## **3. Photocatalytic activity of TiO2/metal composite films**

Although the photocatalytic activity of TiO2 under ultraviolet and visible light irradiation has been investigated around the world, only the photocatalytic activity of TiO2/metal composite films under ultraviolet irradiation is involved and discussed in this section. Here, we developed evaluation method of photocatalytic activity of TiO2/metal composite films by which we evaluated the photocatalytic activity of TiO2/Ti and TiO2/Cu composite films fabricated by MCT.

## **3.1. Evaluation method of photocatalytic activity**

We developed evaluation method of photocatalytic activity of the TiO2/metal composite films by referring to Japan Industrial Standard (JIS R 1703-2, 2007). The evaluation procedure is as follows. Before the evaluation of photocatalytic activity, pre-adsorption of methylene blue (MB) is carried out to obtain the same initial evaluation condition for all the samples. Firstly, the cleaned samples are dispersed uniformly to form a layer of samples on the bottom of a cylinder-shaped cell with a dimension of Φ18 × 50 mm. Subsequently, 3 *ml* MB solution with a concentration of 20 *μmol*/*l* is poured into the cell. The cell with the samples and MB solution is kept in a totally dark place for 12 h. Then, the evaluation of the photocatalytic activity will be carried out. The samples after pre-adsorption are laid uniformly on the bottom of a same cell to form a layer of samples and 7 *ml* MB solution with a concentration of 10 *μmol*/*l* is poured into the cell. The schematic diagram of the evaluation of photocatalytic activity is shown in Fig. 24. A colorimeter (Sanshin Industrial Co., Ltd) of 660 nm in UV radiation wavelength, which is near the peak of absorption spectrum of MB solution (664 nm), is used to measure the absorbance of MB solution. The UV irradiation time is 24 h. Besides, both of the pre-adsorption and the evaluation of photocatalytic activity are carried out at room temperature. The gradient, *k* of MB solution concentrationirradiation time curve is calculated by the least-squares method with the data from 1 to 12 h and *k* is used as the degradation rate constants. The higher the degradation rate constants *k*, the higher the photocatalytic activity.

Mechanical Coating Technique for Composite Films and Composite Photocatalyst Films 341

degrees in the case of the other samples. That means MB was degraded under the action of UV light and TiO2 samples. In other word, the samples fabricated by MCT and its following

<sup>0</sup> <sup>10</sup> <sup>20</sup> <sup>6</sup>

The degradation rate constants, *k* are also given in Fig. 26. It can be seen that the degradation rate constants, *k* increased with the increase of oxidation temperature and reached the peak value at 723 K above which the degradation rate constants, *k* decreased. Combined with the XRD patterns in Fig. 14, the evolution of the photocatalytic activity can be discussed as follows. When oxidation temperature was below 623 K, the peaks of TiO2 were not detected which means Ti films were not oxidized or were oxidized sufficiently. Therefore, the photocatalytic activity of the films was low as shown in Fig. 26. With the increase of oxidation temperature from 623 to 773 K, more Ti films were oxidized and TiO2/Ti composite films were formed. The improvement of photocatalytic activity should relate to the composite microstructure of TiO2 and Ti. According to charge separation effect (Rengaraj et al., 2007), electrons in TiO2 may transfer to metals with higher work functions. The electron transfer can decrease the recombination velocity of electron-hole pairs in TiO2. It can improve the photocatalytic activity of TiO2. When oxidation temperature was 723 K, the composite films obtained the optimum ratio of TiO2 to Ti. It resulted in the highest photocatalytic activity. When oxidation temperature was above 773 K, the oxidation degree of Ti films was further increased and Ti films were completely oxidized when oxidation temperature was above a certain value. Although the amounts of TiO2 increased, the

**Figure 25.** MB solution concentration as a function of UV irradiation time under the action of the

photocatalytic activity decreased due to the weakening of charge separation effect.

The degradation rate constants, *k* as a function of 2nd step MCT time are shown in Fig. 27. In the case of nano-sized TiO2 powder (Fig. 27(a)), the samples fabricated without ceramic impact balls showed the highest photocatalytic activity and the degradation rate constants, *k*

photocatalytic activity was decreased. On the other hand, the samples fabricated with Al2O3 impact balls showed the greatest photocatalytic activity in the case of micron-sized TiO2


samples fabricated by MCT and the following high-temperature oxidation

UV irradiation time / h

M10-Ti M10-723-20 M10-573-20 M10-773-20 M10-623-20 M10-873-20 M10-673-20 M10-973-20

high-temperature oxidation showed photocatalytic activity.

7

8

MB solution concentration /

exceeded 350 nmol·*l*

9

10

11

*μmol*

**Figure 24.** Photocatalytic activity evaluation of TiO2/metal composite films fabricated by MCT

### **3.2. Photocatalytic activity of TiO2/Ti composite films**

Fig. 25 shows the evolution of MB solution concentration as UV irradiation time under the action of TiO2/Ti composite films fabricated by MCT and its following high-temperature oxidation as described in Section 2.4. MB solution concentration slight increased in the case of M10-Ti and M10-573-20. Meanwhile, MB solution concentration decreased in varying degrees in the case of the other samples. That means MB was degraded under the action of UV light and TiO2 samples. In other word, the samples fabricated by MCT and its following high-temperature oxidation showed photocatalytic activity.

340 Composites and Their Applications

the higher the photocatalytic activity.

Black lights

**Figure 24.** Photocatalytic activity evaluation of TiO2/metal composite films fabricated by MCT

Fig. 25 shows the evolution of MB solution concentration as UV irradiation time under the action of TiO2/Ti composite films fabricated by MCT and its following high-temperature oxidation as described in Section 2.4. MB solution concentration slight increased in the case of M10-Ti and M10-573-20. Meanwhile, MB solution concentration decreased in varying

**3.2. Photocatalytic activity of TiO2/Ti composite films** 

**3.1. Evaluation method of photocatalytic activity** 

We developed evaluation method of photocatalytic activity of the TiO2/metal composite films by referring to Japan Industrial Standard (JIS R 1703-2, 2007). The evaluation procedure is as follows. Before the evaluation of photocatalytic activity, pre-adsorption of methylene blue (MB) is carried out to obtain the same initial evaluation condition for all the samples. Firstly, the cleaned samples are dispersed uniformly to form a layer of samples on the bottom of a cylinder-shaped cell with a dimension of Φ18 × 50 mm. Subsequently, 3 *ml* MB solution with a concentration of 20 *μmol*/*l* is poured into the cell. The cell with the samples and MB solution is kept in a totally dark place for 12 h. Then, the evaluation of the photocatalytic activity will be carried out. The samples after pre-adsorption are laid uniformly on the bottom of a same cell to form a layer of samples and 7 *ml* MB solution with a concentration of 10 *μmol*/*l* is poured into the cell. The schematic diagram of the evaluation of photocatalytic activity is shown in Fig. 24. A colorimeter (Sanshin Industrial Co., Ltd) of 660 nm in UV radiation wavelength, which is near the peak of absorption spectrum of MB solution (664 nm), is used to measure the absorbance of MB solution. The UV irradiation time is 24 h. Besides, both of the pre-adsorption and the evaluation of photocatalytic activity are carried out at room temperature. The gradient, *k* of MB solution concentrationirradiation time curve is calculated by the least-squares method with the data from 1 to 12 h and *k* is used as the degradation rate constants. The higher the degradation rate constants *k*,

> Al2O3 balls coated with TiO2/Ti composite films

MB solution (10 *µmol/l*)

)

UV light (1 mW/cm2

**Figure 25.** MB solution concentration as a function of UV irradiation time under the action of the samples fabricated by MCT and the following high-temperature oxidation

The degradation rate constants, *k* are also given in Fig. 26. It can be seen that the degradation rate constants, *k* increased with the increase of oxidation temperature and reached the peak value at 723 K above which the degradation rate constants, *k* decreased. Combined with the XRD patterns in Fig. 14, the evolution of the photocatalytic activity can be discussed as follows. When oxidation temperature was below 623 K, the peaks of TiO2 were not detected which means Ti films were not oxidized or were oxidized sufficiently. Therefore, the photocatalytic activity of the films was low as shown in Fig. 26. With the increase of oxidation temperature from 623 to 773 K, more Ti films were oxidized and TiO2/Ti composite films were formed. The improvement of photocatalytic activity should relate to the composite microstructure of TiO2 and Ti. According to charge separation effect (Rengaraj et al., 2007), electrons in TiO2 may transfer to metals with higher work functions. The electron transfer can decrease the recombination velocity of electron-hole pairs in TiO2. It can improve the photocatalytic activity of TiO2. When oxidation temperature was 723 K, the composite films obtained the optimum ratio of TiO2 to Ti. It resulted in the highest photocatalytic activity. When oxidation temperature was above 773 K, the oxidation degree of Ti films was further increased and Ti films were completely oxidized when oxidation temperature was above a certain value. Although the amounts of TiO2 increased, the photocatalytic activity decreased due to the weakening of charge separation effect.

The degradation rate constants, *k* as a function of 2nd step MCT time are shown in Fig. 27. In the case of nano-sized TiO2 powder (Fig. 27(a)), the samples fabricated without ceramic impact balls showed the highest photocatalytic activity and the degradation rate constants, *k* exceeded 350 nmol·*l* -1·*h*-1. After the introduction of ceramic impact balls into 2-step MCT, the photocatalytic activity was decreased. On the other hand, the samples fabricated with Al2O3 impact balls showed the greatest photocatalytic activity in the case of micron-sized TiO2

powder (Fig. 27(b)). Compared with the TiO2/Ti composite films fabricated with micronsized TiO2 powder, the composite films fabricated with nano-sized TiO2 powder showed much higher photocatalytic activity. It should relate to the higher specific area of nano-sized TiO2 powder particles. From Fig. 26 and 27, anatase TiO2/Ti composite films showed much higher photocatalytic activity than that of rutile TiO2/Ti composite films. It is well known that anatase TiO2 generally shows higher photocatalytic activity than rutile TiO2.

Mechanical Coating Technique for Composite Films and Composite Photocatalyst Films 343

photocatalytic activity of the composite films (Lu et al., 2011 b). The composite films after the high-temperature oxidation were characterized and their photocatalytic activity was also evaluated. In addition, the effect on high-temperature oxidation on the microstructure and

Firstly, TiO2/Ti composite films were prepared by 2-step MCT as described in Section 2.5.1. Ti powder with a purity of 99.1% and an average diameter of 30 μm was used as the coating material. Al2O3 balls with an average diameter of 1 mm were used as the substrates. After the formation of Ti films on Al2O3 balls, anatase TiO2 powder with an average diameter of 0.45 m (Kishida Chemical Co. Ltd., Japan) was used to form TiO2/Ti composite films. To make the composite films strong enough, Al2O3 or WC balls with the diameter of 10 mm were introduced into the fabrication of the composite films. The schematic diagram can be seen in Fig. 15. Subsequently, high-temperature oxidation was carried out for the TiO2/Ti composite films fabricated by 2-step MCT. The oxidation temperature was set at 673, 773 and 873 K and the oxidation time was 10 h. The denotations of the samples fabricated by 2-

the photocatalytic activity of the composite films was also discussed.

step MCT and the following high-temperature oxidation are listed in Table 5.

TiO2 powder Impact ball Sample maker

Note: *x* means the 2nd step MCT time, *y* is oxidation temperature. **Table 5.** Denotations of the samples fabricated by 2-step MCT and the following high-temperature

Fig. 28 shows the appearances of the samples fabricated by 2-step MCT and the following high-temperature oxidation. The samples lost metallic luster and became white compared with the Ti film-coated Al2O3 balls. Also, dark and uneven areas can also be seen. The surface SEM images of the samples are shown in Fig. 29. The surface color of the samples seems to be uniform except for some point areas. It indicates that the uniform TiO2 films were formed. However, for the TiO2/Ti composite films fabricated by 2-step MCT there are

The SEM images of the cross sections of the samples are given in Fig. 30. It can be seen that a composite microstructure of TiO2 films and Ti films formed. In other words, TiO2/Ti composite films were fabricated. The TiO2 films consisted of the deposited TiO2 in the second step of 2-step MCT and the TiO2 formed in high-temperature oxidation. From the above results, it can be concluded that the loading amounts of TiO2 in the composite films

light and dark areas corresponding to Ti and TiO2 respectively shown in Fig. 17.


*3.3.1. Improved fabrication processes* 

TiO2-K

*3.3.2. Characterization of the TiO2/Ti composite films* 

were increased by high-temperature oxidation.

oxidation

**Figure 26.** Degradation rate constants, *k* as a function of oxidation temperature

(a) TiO2 powder with the average diameter of 7 nm (b) TiO2 powder with the average diameter of 0.45 μm **Figure 27.** Degradation rate constants, *k* as a function of 2nd step MCT time

#### **3.3. Improvement of photocatalytic activity by high-temperature oxidation**

High-temperature oxidation was carried out to increase the crystallinity and the volumes of TiO2 in TiO2/Ti composite films fabricated by 2-step MCT and therefore improve the photocatalytic activity of the composite films (Lu et al., 2011 b). The composite films after the high-temperature oxidation were characterized and their photocatalytic activity was also evaluated. In addition, the effect on high-temperature oxidation on the microstructure and the photocatalytic activity of the composite films was also discussed.

#### *3.3.1. Improved fabrication processes*

342 Composites and Their Applications

powder (Fig. 27(b)). Compared with the TiO2/Ti composite films fabricated with micronsized TiO2 powder, the composite films fabricated with nano-sized TiO2 powder showed much higher photocatalytic activity. It should relate to the higher specific area of nano-sized TiO2 powder particles. From Fig. 26 and 27, anatase TiO2/Ti composite films showed much higher photocatalytic activity than that of rutile TiO2/Ti composite films. It is well known

that anatase TiO2 generally shows higher photocatalytic activity than rutile TiO2.

(TiO2+Ti)

Composite films TiO2 films

0

100

200

0 2 4 6 8 10

2nd step MCT Time / h (b) TiO2 powder with the average diameter of 0.45 μm

ϕ10W-CM*x*K ϕ10A-CM*x*K

<sup>300</sup> CM*x*<sup>K</sup>

Incomplete oxidation

**Figure 26.** Degradation rate constants, *k* as a function of oxidation temperature

CM*x*S

ϕ10W-CM*x*S ϕ10A-CM*x*S

(a) TiO2 powder with the average diameter of 7 nm

0

100

200

*k* 

*/* nmol*· l-1·*h*-1*

300

400

500

0 2 4 6 8 10

2nd step MCT Time / h

**Figure 27.** Degradation rate constants, *k* as a function of 2nd step MCT time

**3.3. Improvement of photocatalytic activity by high-temperature oxidation** 

High-temperature oxidation was carried out to increase the crystallinity and the volumes of TiO2 in TiO2/Ti composite films fabricated by 2-step MCT and therefore improve the Firstly, TiO2/Ti composite films were prepared by 2-step MCT as described in Section 2.5.1. Ti powder with a purity of 99.1% and an average diameter of 30 μm was used as the coating material. Al2O3 balls with an average diameter of 1 mm were used as the substrates. After the formation of Ti films on Al2O3 balls, anatase TiO2 powder with an average diameter of 0.45 m (Kishida Chemical Co. Ltd., Japan) was used to form TiO2/Ti composite films. To make the composite films strong enough, Al2O3 or WC balls with the diameter of 10 mm were introduced into the fabrication of the composite films. The schematic diagram can be seen in Fig. 15. Subsequently, high-temperature oxidation was carried out for the TiO2/Ti composite films fabricated by 2-step MCT. The oxidation temperature was set at 673, 773 and 873 K and the oxidation time was 10 h. The denotations of the samples fabricated by 2 step MCT and the following high-temperature oxidation are listed in Table 5.


Note: *x* means the 2nd step MCT time, *y* is oxidation temperature.

**Table 5.** Denotations of the samples fabricated by 2-step MCT and the following high-temperature oxidation

#### *3.3.2. Characterization of the TiO2/Ti composite films*

Fig. 28 shows the appearances of the samples fabricated by 2-step MCT and the following high-temperature oxidation. The samples lost metallic luster and became white compared with the Ti film-coated Al2O3 balls. Also, dark and uneven areas can also be seen. The surface SEM images of the samples are shown in Fig. 29. The surface color of the samples seems to be uniform except for some point areas. It indicates that the uniform TiO2 films were formed. However, for the TiO2/Ti composite films fabricated by 2-step MCT there are light and dark areas corresponding to Ti and TiO2 respectively shown in Fig. 17.

The SEM images of the cross sections of the samples are given in Fig. 30. It can be seen that a composite microstructure of TiO2 films and Ti films formed. In other words, TiO2/Ti composite films were fabricated. The TiO2 films consisted of the deposited TiO2 in the second step of 2-step MCT and the TiO2 formed in high-temperature oxidation. From the above results, it can be concluded that the loading amounts of TiO2 in the composite films were increased by high-temperature oxidation.

Mechanical Coating Technique for Composite Films and Composite Photocatalyst Films 345

ϕ10W-CM6K-873 ϕ10W-CM6K-673

ϕ10W-CM6K ϕ10W-CM3K-873 ϕ10W-CM3K-673

ϕ10W-CM3K

(a) 2-step MCT with Al2O3 impact balls (b) 2-step MCT with WC impact balls

**Figure 31.** XRD patterns of the samples fabricated by 2-step MCT and the following high-temperature

The degradation rate constants, *k* as a function of oxidation temperature are shown in Fig. 32. For the samples fabricated by 2-step MCT with Al2O3 impact balls (Fig. 32(a)), they showed their highest photocatalytic activity when oxidation temperature was 673 K. When the 2nd MCT was 3 h, the composite films showed the greatest photocatalytic activity. On the other hand, for those fabricated by 2-step MCT with WC impact balls (Fig. 32(b)), the samples showed the similar evolution of photocatalytic activity except the Φ 10W-CM3K samples. However, their photocatalytic activity was much lower than those fabricated by 2 step MCT with Al2O3 impact balls. It may relate to the smaller loading amounts of anatase TiO2 as WC impact balls exerted greater impact force and resulted in the exfoliation of the

30 40 50

2θ / deg

Fig. 31 shows the XRD patterns of the samples fabricated by 2-step MCT and the following high-temperature oxidation at 673 and 873 K. For all the samples, Ti peaks and anatase TiO2 peaks were detected while the later was rather weak due to its small loading amounts during the second step in 2-step MCT. When oxidation temperature was 873 K, the peaks of rutile TiO2 were detected which means rutile TiO2 was formed in the high-temperature oxidation. For the sample Φ 10W-CM6K-673 K, a weak peak of rutile TiO2 at about 27.5º (2θ) was be found. It indicates that rutile TiO2 formed when oxidation temperature was 673 K

although the amount was rather small.

TiO2 (anatase)

ϕ10A-CM6K-873

TiO2 Ti (rutile)

Al2O3

ϕ10A-CM6K-673 ϕ10A-CM6K ϕ10A-CM3K-873

ϕ10A-CM3K-673 ϕ10A-CM3K

30 40 50

*3.3.3. Photocatalytic activity of the TiO2/Ti composite films* 

2θ / deg

Diffraction intensity / a. u.

oxidation

adhered TiO2.

**Figure 28.** Appearances of the samples fabricated by 2-step MCT and the following high-temperature oxidation

**Figure 29.** Surface SEM images of the samples fabricated by 2-step MCT and the following hightemperature oxidation

**Figure 30.** SEM images of the cross sections of the samples fabricated by 2-step MCT and the following high-temperature oxidation

Fig. 31 shows the XRD patterns of the samples fabricated by 2-step MCT and the following high-temperature oxidation at 673 and 873 K. For all the samples, Ti peaks and anatase TiO2 peaks were detected while the later was rather weak due to its small loading amounts during the second step in 2-step MCT. When oxidation temperature was 873 K, the peaks of rutile TiO2 were detected which means rutile TiO2 was formed in the high-temperature oxidation. For the sample Φ 10W-CM6K-673 K, a weak peak of rutile TiO2 at about 27.5º (2θ) was be found. It indicates that rutile TiO2 formed when oxidation temperature was 673 K although the amount was rather small.

344 Composites and Their Applications

oxidation

temperature oxidation

high-temperature oxidation

Al2O3

ϕ 10A-CM3K

ϕ 10W-CM3K

ϕ 10W-CM6K

ϕ 10A-CM3K-673

ϕ 10W-CM3K-673

ϕ 10W-CM6K-673

**Figure 28.** Appearances of the samples fabricated by 2-step MCT and the following high-temperature

(c) ? 10A-CM3K-873 (d) ? 10W-CM3K-873

(a) ϕ 10A-CM3K-873 (b) ϕ 10W-CM3K-873

**Figure 30.** SEM images of the cross sections of the samples fabricated by 2-step MCT and the following

30μm

Ti

TiO2

**Figure 29.** Surface SEM images of the samples fabricated by 2-step MCT and the following high-

(a) ? 10A-CM3K-773 (b) ? 10W-CM3K-773

ϕ 10A-CM3K-873

ϕ 10W-CM3K-873

1mm

100µm

Al2O3

ϕ 10W-CM6K-873

**Figure 31.** XRD patterns of the samples fabricated by 2-step MCT and the following high-temperature oxidation

#### *3.3.3. Photocatalytic activity of the TiO2/Ti composite films*

The degradation rate constants, *k* as a function of oxidation temperature are shown in Fig. 32. For the samples fabricated by 2-step MCT with Al2O3 impact balls (Fig. 32(a)), they showed their highest photocatalytic activity when oxidation temperature was 673 K. When the 2nd MCT was 3 h, the composite films showed the greatest photocatalytic activity. On the other hand, for those fabricated by 2-step MCT with WC impact balls (Fig. 32(b)), the samples showed the similar evolution of photocatalytic activity except the Φ 10W-CM3K samples. However, their photocatalytic activity was much lower than those fabricated by 2 step MCT with Al2O3 impact balls. It may relate to the smaller loading amounts of anatase TiO2 as WC impact balls exerted greater impact force and resulted in the exfoliation of the adhered TiO2.

The improvement of photocatalytic activity should result from the microstructure and phase evolution of the composite films. As discussed in Fig. 31, Ti films were oxidized partly and rutile TiO2 was formed when oxidation temperature was 673 K and anatase TiO2 was reserved at that temperature. Therefore, a composite microstructure of Ti, anatase TiO2 and rutile TiO2 was formed. Charge separation effect and mixed crystal effect might work which can improve photocatalytic activity (Cao et al., 2009). With the increase of oxidation temperature to 873 K, the volume ratio of rutile TiO2 in the composite films increased. It might lead that the charge separation effect and mixed crystal effect were restrained and therefore decreased the photocatalytic activity of the composite films.

Mechanical Coating Technique for Composite Films and Composite Photocatalyst Films 347

Al2O3 ball mass [g]

80 99.8 60 93.0 400 40 99.8 60 93.0 480

Al2O3 ball purity [%]

1mm

1mm

Rotation speed [rpm]

rotation speed was also changed as shown in Table 6. Secondly, TiO2/Cu composite films were fabricated. 15 g Cu film-coated Al2O3 balls and 13 g anatase TiO2 powder with the average diameter of 7 nm (ST-01, Ishihara Sangyo, Japan) were used as the substrates and the coating material respectively. To make the composite films stronger, 20 Al2O3 impact balls with the diameter of 10 mm were simultaneously put into the bowl. The rotation speed

> Average size of Cu [μm] 40 10

Fig. 33 shows the appearances of the Cu-coated Al2O3 balls after MCT at 400 rpm with the relevant parameters in the experiment number 1 shown in Table 6. It can be seen that the color of the samples changed from white to red brown with the increase of 1st step MCT time. It means that more Cu powder adhered to the surfaces of Al2O3 balls. SEM results revealed that Cu films in this experimental condition were formed when it came to 54 h. Fig. 34 shows the appearances of the samples after 2-step MCT. The color of the samples also changed with the increase of 2nd step MCT time. It indicates that the loading amounts of TiO2 in the composite films changed. The SEM images of the cross sections of the samples are given in Fig. 35. TiO2 adhered to Cu films (Fig. 35 (a)) and some Cu particles inlaid into TiO2 films (Fig. 35 (b)). Therefore, it can be said that a composite microstructure of TiO2 and

0 10 30 54 h

1 h 3 h 6 h 10 h

**Table 6.** Source materials and experimental conditions for fabrication of Cu films by MCT

was set at 400 rpm and the 2nd MCT time was 1, 3, 6 and 10 h.

Cu purity [%]

Cu powder mass [g]

*3.4.2. Characterization of TiO2/Cu composite films* 

**Figure 33.** Appearances of the Cu-coated Al2O3 balls after MCT

**Figure 34.** Appearances of the samples after 2-step MCT

1 2

Cu formed.

Experiment number

**Figure 32.** Degradation rate constants, *k* as a function of oxidation temperature

## **3.4. TiO2/Cu composite photocatalyst films**

In this section, we will describe and discuss the fabrication of TiO2/Cu composite films by 2 step MCT. The composite films were characterized by XRD and SEM. The formation of Cu films and TiO2/Cu composite films was also examined. The photocatalytic activity of the composite films was evaluated by measuring the degradation rate constants, *k* of MB under the UV irradiation.

#### *3.4.1. Fabrication of TiO2/Cu composite films*

TiO2/Cu composite films were fabricated by 2-step MCT as shown in Fig. 15. Firstly, Cu films were fabricated. The source materials and the experimental condition are listed in Table 6. To improve the production efficiency, Cu powders with different average diameters were used as the coating materials. Meanwhile, the loading amounts of Cu powder and the rotation speed was also changed as shown in Table 6. Secondly, TiO2/Cu composite films were fabricated. 15 g Cu film-coated Al2O3 balls and 13 g anatase TiO2 powder with the average diameter of 7 nm (ST-01, Ishihara Sangyo, Japan) were used as the substrates and the coating material respectively. To make the composite films stronger, 20 Al2O3 impact balls with the diameter of 10 mm were simultaneously put into the bowl. The rotation speed was set at 400 rpm and the 2nd MCT time was 1, 3, 6 and 10 h.


**Table 6.** Source materials and experimental conditions for fabrication of Cu films by MCT

#### *3.4.2. Characterization of TiO2/Cu composite films*

346 Composites and Their Applications

0

the UV irradiation.

100

*k*

/nmol·*l*-1·h-1

200

300

400

The improvement of photocatalytic activity should result from the microstructure and phase evolution of the composite films. As discussed in Fig. 31, Ti films were oxidized partly and rutile TiO2 was formed when oxidation temperature was 673 K and anatase TiO2 was reserved at that temperature. Therefore, a composite microstructure of Ti, anatase TiO2 and rutile TiO2 was formed. Charge separation effect and mixed crystal effect might work which can improve photocatalytic activity (Cao et al., 2009). With the increase of oxidation temperature to 873 K, the volume ratio of rutile TiO2 in the composite films increased. It might lead that the charge separation effect and mixed crystal effect were restrained and

0

In this section, we will describe and discuss the fabrication of TiO2/Cu composite films by 2 step MCT. The composite films were characterized by XRD and SEM. The formation of Cu films and TiO2/Cu composite films was also examined. The photocatalytic activity of the composite films was evaluated by measuring the degradation rate constants, *k* of MB under

TiO2/Cu composite films were fabricated by 2-step MCT as shown in Fig. 15. Firstly, Cu films were fabricated. The source materials and the experimental condition are listed in Table 6. To improve the production efficiency, Cu powders with different average diameters were used as the coating materials. Meanwhile, the loading amounts of Cu powder and the

100

200

300

400

300 400 500 600 700 800

ϕ10W-CM3K ϕ10W-CM6K M10-Ti

Oxidation temperature / K

(b) with WC impact balls

therefore decreased the photocatalytic activity of the composite films.

ϕ 10A-CM3K ϕ 10A-CM6K M10-Ti 300 400 500 600 700 800

Oxidation temperature / K

(a) with Al2O3 impact balls

**3.4. TiO2/Cu composite photocatalyst films** 

*3.4.1. Fabrication of TiO2/Cu composite films* 

**Figure 32.** Degradation rate constants, *k* as a function of oxidation temperature

Fig. 33 shows the appearances of the Cu-coated Al2O3 balls after MCT at 400 rpm with the relevant parameters in the experiment number 1 shown in Table 6. It can be seen that the color of the samples changed from white to red brown with the increase of 1st step MCT time. It means that more Cu powder adhered to the surfaces of Al2O3 balls. SEM results revealed that Cu films in this experimental condition were formed when it came to 54 h. Fig. 34 shows the appearances of the samples after 2-step MCT. The color of the samples also changed with the increase of 2nd step MCT time. It indicates that the loading amounts of TiO2 in the composite films changed. The SEM images of the cross sections of the samples are given in Fig. 35. TiO2 adhered to Cu films (Fig. 35 (a)) and some Cu particles inlaid into TiO2 films (Fig. 35 (b)). Therefore, it can be said that a composite microstructure of TiO2 and Cu formed.

**Figure 33.** Appearances of the Cu-coated Al2O3 balls after MCT

**Figure 34.** Appearances of the samples after 2-step MCT

Mechanical Coating Technique for Composite Films and Composite Photocatalyst Films 349

The photocatalytic activity of TiO2/Cu composite films should relate to the loading amounts of TiO2 in the composite films. With increase in 2nd step MCT time, the loading amounts of TiO2 increased. When it came to 3 h, the loading amounts of TiO2 might reach the peak value. After the maximum value, TiO2 that adhered to Cu films began to peel off. The more the loading amounts of TiO2 that deposited on Cu films, the higher the photocatalytic activity. In other words, the photocatalytic activity of TiO2/Cu composite films should be proportional to the loading amounts of TiO2 in the composite films. The formation of TiO2/Cu composite microstructure is considered to be another reason why the photocatalytic activity of the composite films was improved. After formation of the interface of TiO2/Cu, electrons in the conduction of TiO2 will migrate to Cu films through the interface, which can decrease the recombination rate of electron-hole pairs in TiO2. It may result in the improvement of charge separation efficiency (Rengaraj et al., 2007). Then, more electrons are trapped in Cu films for reduction reaction and more holes are held in the valence band of

> 2nd step MCT time / h 0 2 4 6 8 10

Although Cu films and TiO2/Cu composite films were fabricated by MCT, the formation process and its mechanism of Cu films are still unknown. Therefore, the formation process

Because the formation process of Cu films happens in a closed and invisible bowl, it is difficult to determine the evolution of the films. However, it was considered to relate to the collision, friction and welding among the Cu powder particles, the inner wall of the bowl and the ceramic grinding mediums (Lü et al., 1995; Maurice and Courtney, 1990; Maurice and Courtney, 1994; Chattopadhyay et al., 2001). By now, we have tried to analyze the evolution of Cu films by observing the change of ceramic substrates. Fig. 38

and its possible mechanism were examined and will be discussed in this section.

TiO2 for oxidation reaction.

0

**Figure 37.** Degradation rate constants, *k* as a function of the 2nd step MCT time

**4. Formation process of Cu films during MCT** 

100

*k /* n mol*·l-1*

*h-1* 

200

**Figure 35.** SEM images of the cross sections of TiO2/Cu composite films fabricated by 2-step MCT with different the 2nd step MCT times

#### *3.4.3. Photocatalytic activity of TiO2/Cu composite films*

MB solution concentration evolution in the evaluation of the photocatalytic activity of TiO2/Cu composite films is shown in Fig. 36. The concentration of MB solution with the Cu film-coated Al2O3 balls was found to increase slightly with increase of UV irradiation time. It means Cu films did not have photocatalytic activity. On the other hand, under the action of TiO2/Cu composite films and UV irradiation, the concentration of MB solution decreased in varying degrees. It suggests the composite films showed photocatalytic activity. For TiO2/Cu composite films with 3 h of 2nd step MCT time, the MB solution concentration decreased to the minimum value after the same UV irradiation time for all the composite films. The degradation rate constants, *k* is illustrated in Fig. 37. The degradation rate constants, *k* increased with the increase of 2nd step MCT time and reached the peak value when it came to 3 h. After that, the degradation rate constants, *k* decreased with the increase of 2nd step MCT time. It means that the TiO2/Cu composite films fabricated during MCT with 3 h of 2nd step MCT time showed the greatest photocatalytic activity for all the composite films.

**Figure 36.** Evolution of MB solution concentration as a function of UV irradiation time in the evaluation of photocatalytic activity of TiO2/Cu composite films

The photocatalytic activity of TiO2/Cu composite films should relate to the loading amounts of TiO2 in the composite films. With increase in 2nd step MCT time, the loading amounts of TiO2 increased. When it came to 3 h, the loading amounts of TiO2 might reach the peak value. After the maximum value, TiO2 that adhered to Cu films began to peel off. The more the loading amounts of TiO2 that deposited on Cu films, the higher the photocatalytic activity. In other words, the photocatalytic activity of TiO2/Cu composite films should be proportional to the loading amounts of TiO2 in the composite films. The formation of TiO2/Cu composite microstructure is considered to be another reason why the photocatalytic activity of the composite films was improved. After formation of the interface of TiO2/Cu, electrons in the conduction of TiO2 will migrate to Cu films through the interface, which can decrease the recombination rate of electron-hole pairs in TiO2. It may result in the improvement of charge separation efficiency (Rengaraj et al., 2007). Then, more electrons are trapped in Cu films for reduction reaction and more holes are held in the valence band of TiO2 for oxidation reaction.

**Figure 37.** Degradation rate constants, *k* as a function of the 2nd step MCT time

#### **4. Formation process of Cu films during MCT**

348 Composites and Their Applications

30μm

different the 2nd step MCT times

Al2O3

*3.4.3. Photocatalytic activity of TiO2/Cu composite films* 

6

evaluation of photocatalytic activity of TiO2/Cu composite films

7

MB solution concentration

8

9

10

 /

μ

mol·*l*-1

11

(a) 1 h (b) 3 h

**Figure 35.** SEM images of the cross sections of TiO2/Cu composite films fabricated by 2-step MCT with

MB solution concentration evolution in the evaluation of the photocatalytic activity of TiO2/Cu composite films is shown in Fig. 36. The concentration of MB solution with the Cu film-coated Al2O3 balls was found to increase slightly with increase of UV irradiation time. It means Cu films did not have photocatalytic activity. On the other hand, under the action of TiO2/Cu composite films and UV irradiation, the concentration of MB solution decreased in varying degrees. It suggests the composite films showed photocatalytic activity. For TiO2/Cu composite films with 3 h of 2nd step MCT time, the MB solution concentration decreased to the minimum value after the same UV irradiation time for all the composite films. The degradation rate constants, *k* is illustrated in Fig. 37. The degradation rate constants, *k* increased with the increase of 2nd step MCT time and reached the peak value when it came to 3 h. After that, the degradation rate constants, *k* decreased with the increase of 2nd step MCT time. It means that the TiO2/Cu composite films fabricated during MCT with 3 h of 2nd step MCT time showed the greatest photocatalytic activity for all the composite films.

<sup>0</sup> <sup>10</sup> <sup>20</sup> <sup>5</sup>

**Figure 36.** Evolution of MB solution concentration as a function of UV irradiation time in the

UV irradiation time / h

Al2O3

Cu

Cu films

10 h

3 h

1 h 6 h TiO2

Cu

TiO2

Although Cu films and TiO2/Cu composite films were fabricated by MCT, the formation process and its mechanism of Cu films are still unknown. Therefore, the formation process and its possible mechanism were examined and will be discussed in this section.

Because the formation process of Cu films happens in a closed and invisible bowl, it is difficult to determine the evolution of the films. However, it was considered to relate to the collision, friction and welding among the Cu powder particles, the inner wall of the bowl and the ceramic grinding mediums (Lü et al., 1995; Maurice and Courtney, 1990; Maurice and Courtney, 1994; Chattopadhyay et al., 2001). By now, we have tried to analyze the evolution of Cu films by observing the change of ceramic substrates. Fig. 38 shows the SEM images of Cu-coated Al2O3 balls after MCT. The areas of dark and light color correspond to alumina and copper respectively. More Cu particles adhered to the surfaces of Al2O3 balls with the increase of 1st step MCT time. When it came to 54 h, continuous Cu films formed and the thickness was about 10 μm. In other words, the surfaces of Al2O3 balls were totally coated by Cu films. The result is in good agreement with that in Fig. 33.

Mechanical Coating Technique for Composite Films and Composite Photocatalyst Films 351

IV-range

V-range

0 10 20 30 40 50

**Figure 39.** Coverage of Al2O3 ball' surface with Cu as a function of MCT time during MCT

III-range II-range

MCT time / h

Fig. 40 shows the SEM images of the surfaces and the cross sections of the Cu-coated Al2O3 balls after MCT with 480 rpm. It can be observed that continuous Cu films formed when MCT time was 20 h and the average thickness of the films was about 80 μm. Compared with the fabrication of Cu films with Cu powder of 40 μm in average particle size by MCT at 400 rpm (Fig. 38(c)), the fabrication of Cu films with Cu powder of 10 μm in average particle size by MCT at 480 rpm was quicker. In other words, the condition of Cu powder of 10 μm in average particle size and a rotation speed of 480 rpm accelerated the formation

(a) 10 h (b) 20 h

**Figure 40.** SEM images of the Cu-coated Al2O3 balls fabricated with Cu powder of 10μm in average

Cu

Al2O3

100μm

0

300μm

particle size by MCT at 480 rpm

Al2O3

20

40

Coverage with Cu

of Cu films.

60

I-range

Cu films

80

 / %

100

The coverage of Al2O3 ball surface with Cu is illustrated in Fig. 39. The evolution of Cu films during MCT can fall into five ranges. In the first range, the coverage hardly increased. However, Al2O3 balls became dark. Micron-sized Cu particles on the surfaces of Al2O3 balls were not found by SEM. It means that a small quantity of Cu atom clusters might transfer to the surfaces of Al2O3 balls. Under impact and friction force, the atom clusters adhered to the surfaces of Al2O3 balls and nucleated. In the second and third range, more Cu atom clusters adhered to the nuclei of Cu; these nuclei gradually grew up and could be observed by SEM (Fig. 38 (a)). Then discrete islands of Cu connected with each other (Fig. 38 (b)). The growth of Cu nuclei and the connection of discrete islands of Cu resulted in the coverage increase. After the first three ranges, the surfaces of Al2O3 balls were nearly coated with Cu and the coverage was close to 100%. In other words, continuous Cu films formed. Although the experiments were stopped when MCT time reached 54 h, the fourth and fifth ranges are considered to exit as the similar evolution of Fe films has been established in our published work (Hao et al., 2012). In the fourth range, the thickness of continuous Cu films may increase. As deformation of Cu particles, Cu particles become hard and adhesion between Cu particles may become difficult. Finally, exfoliation of Cu films would dominate. From the above results, the evolution of Cu films can fall into nucleation, growth of nuclei and connection, formation of continuous films and thickening, exfoliation of continuous films.

**Figure 38.** SEM images of the surfaces and the cross sections of Cu films fabricated by MCT

**Figure 39.** Coverage of Al2O3 ball' surface with Cu as a function of MCT time during MCT

with that in Fig. 33.

exfoliation of continuous films.

**Al2O3**

**Cu**

**Al2O3**

shows the SEM images of Cu-coated Al2O3 balls after MCT. The areas of dark and light color correspond to alumina and copper respectively. More Cu particles adhered to the surfaces of Al2O3 balls with the increase of 1st step MCT time. When it came to 54 h, continuous Cu films formed and the thickness was about 10 μm. In other words, the surfaces of Al2O3 balls were totally coated by Cu films. The result is in good agreement

The coverage of Al2O3 ball surface with Cu is illustrated in Fig. 39. The evolution of Cu films during MCT can fall into five ranges. In the first range, the coverage hardly increased. However, Al2O3 balls became dark. Micron-sized Cu particles on the surfaces of Al2O3 balls were not found by SEM. It means that a small quantity of Cu atom clusters might transfer to the surfaces of Al2O3 balls. Under impact and friction force, the atom clusters adhered to the surfaces of Al2O3 balls and nucleated. In the second and third range, more Cu atom clusters adhered to the nuclei of Cu; these nuclei gradually grew up and could be observed by SEM (Fig. 38 (a)). Then discrete islands of Cu connected with each other (Fig. 38 (b)). The growth of Cu nuclei and the connection of discrete islands of Cu resulted in the coverage increase. After the first three ranges, the surfaces of Al2O3 balls were nearly coated with Cu and the coverage was close to 100%. In other words, continuous Cu films formed. Although the experiments were stopped when MCT time reached 54 h, the fourth and fifth ranges are considered to exit as the similar evolution of Fe films has been established in our published work (Hao et al., 2012). In the fourth range, the thickness of continuous Cu films may increase. As deformation of Cu particles, Cu particles become hard and adhesion between Cu particles may become difficult. Finally, exfoliation of Cu films would dominate. From the above results, the evolution of Cu films can fall into nucleation, growth of nuclei and connection, formation of continuous films and thickening,

(a) 10 h (b) 22 h (c) 54 h

**Figure 38.** SEM images of the surfaces and the cross sections of Cu films fabricated by MCT

**Al2O3**

**Cu**

**100μm**

300μm

**Al2O3**

Cu

Cu

**Al2O3**

Fig. 40 shows the SEM images of the surfaces and the cross sections of the Cu-coated Al2O3 balls after MCT with 480 rpm. It can be observed that continuous Cu films formed when MCT time was 20 h and the average thickness of the films was about 80 μm. Compared with the fabrication of Cu films with Cu powder of 40 μm in average particle size by MCT at 400 rpm (Fig. 38(c)), the fabrication of Cu films with Cu powder of 10 μm in average particle size by MCT at 480 rpm was quicker. In other words, the condition of Cu powder of 10 μm in average particle size and a rotation speed of 480 rpm accelerated the formation of Cu films.

**Figure 40.** SEM images of the Cu-coated Al2O3 balls fabricated with Cu powder of 10μm in average particle size by MCT at 480 rpm

## **5. Prospect of MCT**

Compared with the traditional film coating techniques such as PVD and CVD, our proposed mechanical coating technique (MCT) shows many advantages including inexpensive equipments, simple process, low preparation cost and large specific area, among others. In addition, it can be performed in air atmosphere at ambient temperature. It can not only fabricate metal/alloy films but also nonmetal/metal composite films such as TiO2/Ti composite photocatalyst films. It is expected to fabricate other functional film materials in the near future.

Mechanical Coating Technique for Composite Films and Composite Photocatalyst Films 353

Gupta, G.; Mondal, K.; Balasubramaniam, R. (2009). In situ nanocrystalline Fe-Si coating by mechanical alloying. Journal of Alloys and Compounds, Vol. 482, pp. 118-122. Hao, L.; Lu, Y.; Asanuma, H.; Guo, J. (2012). The influence of the processing parameters on the formation of iron thin films on alumina balls by mechanical coating technique.

Kobayashi, K. (1995). Formation of coating film on milling balls for mechanical alloying.

Lu, Y.; Hirohashi, M.; Zhang, S. (2005). Fabrication of oxide film by mechanical coating technique, *Proceedings of International Conference on Surfaces, Coatings and Nanostructured* 

Lu, Y.; Yoshida, H.; Nakayama, H.; Hao, L.; Hirohashi, M. (2011 a). Formation of TiO2/Ti composite photocatalyst film by 2-step mechanical coating technique. Materials Science

Lu, Y.; Yoshida, H.; Toh, K.; Hao, L.; Hirohashi, M. (2011 b). Performance improvement of TiO2/Ti composite photocatalyst film by heat oxidation treatment. Materials Science

Lu, Y.; Hao, L.; Toh, K.; Yoshida, H. (2012). Fabrication of TiO2/Cu composite photocatalyst thin film by 2-step mechanical coating technique and its photocatalytic activity.

Lü, L.; Lai, M. O.; Zhang, S. (1995). Modeling of the mechanical-alloying process. Journal of

Mattox, D. M. (2010). Handbook of physical vapor deposition (PVD) processing, William

Maurice, D. R.; Courtney, T.H. (1990). Physics of mechanical alloying, a first report.

Maurice, D. R.; Courtney, T.H. (1994). Modeling of mechanical alloying: part I. deformation, coalescence, and fragmentation mechanisms. Metallurgical and Materials Transactions,

Pierson, H. O. (1999). Handbook of chemical vapor deposition, Noyes Publications and

Rengaraj, S.; Venkataraj, S.; Yeon, J. W.; Kim, Y.; Li, X. Z.; Pang, G. K. H. (2007). Preparation, characterization and application of Nd-TiO2 photocatalyst for the reduction of Cr (VI)

Romankov, S.; Sha, W.; Kaloshkin, S. D.; Kaevitser, K. (2006). Formation of Ti-Al coatings by mechanical alloying method. Surface Coatings Technology, Vol. 201, pp. 3235-

Suryanarayana, C. (2001). Mechanical alloying and milling. Progress of Materials Science,

Journal of Materials Processing Technology, Vol. 212, pp. 1169-1176.

Japan Industrial Standard, JIS K 7194, 1994. Japan Industrial Standard, JIS R 1703-2, 2007.

*Materials*, Aveiro, Portugal.

Vol. A25, pp. 147-158.

3245.

Vol. 46, pp. 1-184.

Forum, Vol. 675-677, pp. 1229-1232.

Forum, Vol. 675-677, pp. 1233-1236.

Advanced Materials Research, Vol. 415-417, pp. 1942-1948.

Andrew Publication, ISBN 978-0-8155-2037-5, Burlington, USA

Metallurgical and Materials Transactions, Vol. A21, pp. 289-303.

William Andrew Publication, ISBN 0-8155-1432-8, New York, USA

under UV light illumination. Applied Catalysis, Vol. B 77, pp. 157-165.

Materials Processing Technology, Vol. 52, pp. 539-546.

Materials Transactions, Vol. 36, pp. 134-137.

We will continue to advance the development of MCT in the fabrication of composite films and promote their applications. Our main research subjects within next few years are listed as follows.


## **Author details**

Yun Lu *Graduate School & Faculty of Engineering, Chiba University, Japan* 

Liang Hao *Graduate School, Chiba University, Japan* 

Hiroyuki Yoshida *Chiba Industrial Technology Research Institute, Japan* 

## **6. References**


Japan Industrial Standard, JIS K 7194, 1994.

352 Composites and Their Applications

**5. Prospect of MCT** 

the near future.

purification, and so on.

*Graduate School, Chiba University, Japan* 

*Chiba Industrial Technology Research Institute, Japan* 

**Author details** 

Hiroyuki Yoshida

**6. References** 

1088-1092.

85-94.

Yun Lu

Liang Hao

as follows.

Compared with the traditional film coating techniques such as PVD and CVD, our proposed mechanical coating technique (MCT) shows many advantages including inexpensive equipments, simple process, low preparation cost and large specific area, among others. In addition, it can be performed in air atmosphere at ambient temperature. It can not only fabricate metal/alloy films but also nonmetal/metal composite films such as TiO2/Ti composite photocatalyst films. It is expected to fabricate other functional film materials in

We will continue to advance the development of MCT in the fabrication of composite films and promote their applications. Our main research subjects within next few years are listed

5. Application investigation of TiO2/metal composite films in sterilization, environment

Cao, Y. Q.; Long, H. J.; Chen, Y. M.; Cao, Y. A. (2009). Photocatalytic activity of TiO2 films with rutile/anatase mixed crystal structures. Acta Physico-Chimica Sinica, Vol. 25,pp.

Chattopadhyay, P. P.; Manna, I.; Talapatra, S.; Pabi, S. K. (2001). A mathematical analysis of milling mechanics in a planetary ball mill. Materials Chemistry and Physics, Vol. 68, pp.

Farahbakhsh, I.; Zakeri, A.; Manikandan, P.; Hokamoto, K. (2011). Evaluation of nanostructured coating layers formed on Ni balls during mechanical alloying of Cu

1. Analysis on evolution and the relevant mechanism of metal films 2. Theory construction on film formation and numerical simulation 3. Fabrication of visible light-responsive TiO2/metal composite films 4. Improvement on photocatalytic activity of TiO2/metal composite films

*Graduate School & Faculty of Engineering, Chiba University, Japan* 

powder. Applied Surface Science, Vol. 257, pp. 2830-2837.


Yoshida, H.; Lu, Y.; Nakayama, H.; Sano, H.; Hirohashi, M. (2008). Fabrication and evaluation of composite photocatalytic film by mechanical coating technique, *Proceedings of the 6th International Forum on Advanced Material Science and Technology*, Hong Kong, China

**Section 5** 

**Other Applications of Composites** 


**Other Applications of Composites** 

354 Composites and Their Applications

Hong Kong, China

Japan, Vol. 46, pp. 141-146.

Compounds, Vol. 475, pp. 383-386.

ISBN 978-4-274-20519-4, Tokyo, Japan

Yoshida, H.; Lu, Y.; Nakayama, H.; Sano, H.; Hirohashi, M. (2008). Fabrication and evaluation of composite photocatalytic film by mechanical coating technique, *Proceedings of the 6th International Forum on Advanced Material Science and Technology*,

Yoshida, H.; Lu, Y.; Nakayama, H.; Hirohashi, M. (2009 a). Analysis of Ti films fabricated by mechanical coating technique (In Japanese). Journal of Materials Science Society of

Yoshida, H.; Lu, Y.; Nakayama, H.; Hirohashi, M. (2009 b). Fabrication of TiO2 film by mechanical coating technique and its photocatalytic activity. Journal of Alloys and

Yoshida, S.; Taga, Y.; Kinbara, A.; et al. (2008). Handbook of thin films, Ohmsha Publication,

**Chapter 0**

**Chapter 14**

**Carbon Fibre Sensor: Theory and Application**

The piezoresistive1 carbon fibre sensor (CFS) consists of a single carbon fibre roving with electrical connected endings embedded in a sensor carrier (patch) for electrical insulation. Depending on the requirements of the application different patch types (e.g. glass fibre reinforced plastic (GFRP), polyester film, neat epoxy resin) are used. In terms of the mechanical properties GFRP is a particularly suitable patch material. CFSs with a GFRP patch exhibits an improved linearity of the signal due to the supportive effect of the glass fibres to the carbon sensor fibre especially in the case of compression loading. In [6] the ex-PAN fibre T300B was identified as one suitable carbon fibre for CFSs because of the excellent linear piezoresistive behaviour, the high specific resistivity and a high breaking elongation of the

fibre. Figure 1 shows a CFS with a single layer GFRP patch (UD prepreg EG/913).

sensor fibre (T300B 1K) GFRP patch (EG/913)

**Figure 1.** Carbon fibre sensor with an ex-Pan sensor fibre and a GFRP patch

properly cited.

<sup>1</sup> Piezoresitivity describes the change in electrical resistance of a conductor due to an applied strain.

galvanized ending with soldered pin

© 2012 Horoschenkoff and Christner, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is

distribution, and reproduction in any medium, provided the original work is properly cited.

© 2012 Horoschenkoff and Christner, licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

Alexander Horoschenkoff and Christian Christner

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/50504

**1. Introduction**

## **Carbon Fibre Sensor: Theory and Application**

Alexander Horoschenkoff and Christian Christner

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/50504

## **1. Introduction**

The piezoresistive1 carbon fibre sensor (CFS) consists of a single carbon fibre roving with electrical connected endings embedded in a sensor carrier (patch) for electrical insulation. Depending on the requirements of the application different patch types (e.g. glass fibre reinforced plastic (GFRP), polyester film, neat epoxy resin) are used. In terms of the mechanical properties GFRP is a particularly suitable patch material. CFSs with a GFRP patch exhibits an improved linearity of the signal due to the supportive effect of the glass fibres to the carbon sensor fibre especially in the case of compression loading. In [6] the ex-PAN fibre T300B was identified as one suitable carbon fibre for CFSs because of the excellent linear piezoresistive behaviour, the high specific resistivity and a high breaking elongation of the fibre. Figure 1 shows a CFS with a single layer GFRP patch (UD prepreg EG/913).

**Figure 1.** Carbon fibre sensor with an ex-Pan sensor fibre and a GFRP patch

<sup>1</sup> Piezoresitivity describes the change in electrical resistance of a conductor due to an applied strain.

© 2012 Horoschenkoff and Christner, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 Horoschenkoff and Christner, licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

#### 2 Will-be-set-by-IN-TECH 358 Composites and Their Applications Carbon Fibre Sensor: Theory and Application <sup>3</sup>

The manufacturing process of a CFS includes three basic steps: Pre-curing of the carbon fibre, preparation of the electrical connection and embedding of the sensor fibre into the sensor carrier.

The pre-curing process is used to stabilize the carbon fibre roving and to align the filaments of the roving. For this purpose the twisted carbon fibre roving is impregnated by a resin with low viscosity and cured by using a special tooling. Good results for the impregnation of the carbon fibre roving T300B 1K were obtained by using the epoxy resin EP301 S (HBM) and a twist of 20 turns per meter. Spring elements provided a constant tension force along the roving during the curing process at 180 ◦C for 1.5 hours.

For preparation of electrical connections a galvanic process is applied based on a nickel electrolyte. In order to attain a homogeneous nickel coating of the filaments the resin must be removed at the fibre endings2. An applied current of 40 mA for 30 seconds leads to an excellent nickel coating. Depending on the application of the CFS (surface application or structural integration) the ends of the sensor fibre can be provided with soldered pins.

The embedding process of the sensor fibre depends on the used patch type and patch material. Figure 2 shows a micro section of a carbon fibre sensor in longitudinal and transverse direction.

(a) Longitudinal direction (b) Transverse direction

This delocalization of the fourth valence electron leads to a good electrical conductivity of the carbon fibre. The individual layers are held together by weak van der Waals forces (*z*-direction). These different types of bonds within and between the layers result in the anisotropy of the mechanical, thermal and electrical material properties of carbon fibres.

0.142 nm covalent bonds

The degree of crystallinity and the micro structure of carbon fibres are controlled by the carbonisation process and determine the mechanical and electromechanical properties. Concerning ex-PAN fibres the Young's modulus ranges from 200 GPa (HT fibres) to 600 GPa (HM fibres). Ex-pitch fibres have a higher modulus up to 900 GPa. Figure 4 shows the correlation between the Young's modulus and the specific resistivity of different carbon fibre types. The specific resistivity of HT fibres (high tenacity) is in the range of 15 *μ*Ωm up to 18 *μ*Ωm. Higher orientated fibres (IM fibres and HM fibres) show a specific resistivity below

The specific resistance of carbon fibres is strongly temperature dependent [15]. In consequence, temperature effects have a high influence on the signals of CFSs and must be

*R* = *ρ*

*L r*2*π*

considered by an appropriate temperature compensation (see section 3).

The electrical resistance *R* of a carbon fibre is given by:

van der Waals force


Carbon Fibre Sensor: Theory and Application 359

(1)

*x*-*y* plane:

*z*-direction:

0.67 nm

**2.1. Specific resistivity**

**Figure 3.** Graphite structure of crystalline carbon fibres

*x y*

*z*

14 *μ*Ωm.

**2.2. Piezoresistivity**

**Figure 2.** Microsection of a carbon fibre sensor in longitudinal and transverse direction Sensorfibre: 1K roving of the carbon fibre T300B Patch: single layer UD prepreg EG/913

## **2. Electromechanical properties of carbon fibres**

Referring to Chung [2] and Dresselhaus [3] crystalline carbon fibres have the same crystal structure as graphite. The layered and planar structure of crystalline carbon fibres is shown in Figure 3. In each layer the *sp*<sup>2</sup> hybridized carbon atoms are arranged in a hexagonal lattice. Within a layer (*x*-*y* plane) the carbon atoms are bonded by three covalent bonds (overlapping *sp*<sup>2</sup> orbitals), and a metallic bonding is provided by the delocalization of the *pz* orbitals.

<sup>2</sup> For example, the epoxy resin EP 310 S can be burned off or removed using acid.

This delocalization of the fourth valence electron leads to a good electrical conductivity of the carbon fibre. The individual layers are held together by weak van der Waals forces (*z*-direction). These different types of bonds within and between the layers result in the anisotropy of the mechanical, thermal and electrical material properties of carbon fibres.

**Figure 3.** Graphite structure of crystalline carbon fibres

## **2.1. Specific resistivity**

2 Will-be-set-by-IN-TECH

The manufacturing process of a CFS includes three basic steps: Pre-curing of the carbon fibre, preparation of the electrical connection and embedding of the sensor fibre into the sensor

The pre-curing process is used to stabilize the carbon fibre roving and to align the filaments of the roving. For this purpose the twisted carbon fibre roving is impregnated by a resin with low viscosity and cured by using a special tooling. Good results for the impregnation of the carbon fibre roving T300B 1K were obtained by using the epoxy resin EP301 S (HBM) and a twist of 20 turns per meter. Spring elements provided a constant tension force along the

For preparation of electrical connections a galvanic process is applied based on a nickel electrolyte. In order to attain a homogeneous nickel coating of the filaments the resin must be removed at the fibre endings2. An applied current of 40 mA for 30 seconds leads to an excellent nickel coating. Depending on the application of the CFS (surface application or structural integration) the ends of the sensor fibre can be provided with soldered pins.

The embedding process of the sensor fibre depends on the used patch type and patch material. Figure 2 shows a micro section of a carbon fibre sensor in longitudinal and transverse

(a) Longitudinal direction (b) Transverse direction

Referring to Chung [2] and Dresselhaus [3] crystalline carbon fibres have the same crystal structure as graphite. The layered and planar structure of crystalline carbon fibres is shown in Figure 3. In each layer the *sp*<sup>2</sup> hybridized carbon atoms are arranged in a hexagonal lattice. Within a layer (*x*-*y* plane) the carbon atoms are bonded by three covalent bonds (overlapping *sp*<sup>2</sup> orbitals), and a metallic bonding is provided by the delocalization of the *pz* orbitals.

**Figure 2.** Microsection of a carbon fibre sensor in longitudinal and transverse direction

Sensorfibre: 1K roving of the carbon fibre T300B Patch: single layer UD prepreg EG/913

**2. Electromechanical properties of carbon fibres**

<sup>2</sup> For example, the epoxy resin EP 310 S can be burned off or removed using acid.

roving during the curing process at 180 ◦C for 1.5 hours.

carrier.

direction.

The degree of crystallinity and the micro structure of carbon fibres are controlled by the carbonisation process and determine the mechanical and electromechanical properties. Concerning ex-PAN fibres the Young's modulus ranges from 200 GPa (HT fibres) to 600 GPa (HM fibres). Ex-pitch fibres have a higher modulus up to 900 GPa. Figure 4 shows the correlation between the Young's modulus and the specific resistivity of different carbon fibre types. The specific resistivity of HT fibres (high tenacity) is in the range of 15 *μ*Ωm up to 18 *μ*Ωm. Higher orientated fibres (IM fibres and HM fibres) show a specific resistivity below 14 *μ*Ωm.

The specific resistance of carbon fibres is strongly temperature dependent [15]. In consequence, temperature effects have a high influence on the signals of CFSs and must be considered by an appropriate temperature compensation (see section 3).

## **2.2. Piezoresistivity**

The electrical resistance *R* of a carbon fibre is given by:

$$R = \rho \frac{L}{r^2 \pi} \tag{1}$$

**Figure 4.** Correlation between the specific resistance *ρ* and the Young's modulus *E* of different ex-PAN and ex-pitch carbon fibres

where *ρ* is the specific resistivity, *L* the length and *r* the radius of the fibre. The total differential of *R* = *f*(*ρ*, *L*,*r*) is then yielded by the following Equation (2).

$$\mathbf{d}R = \frac{\partial R}{\partial \rho} \mathbf{d}\rho + \frac{\partial R}{\partial L} \mathbf{d}L + \frac{\partial R}{\partial r} \mathbf{d}r = \frac{L}{r^2 \pi} \mathbf{d}\rho + \rho \frac{1}{r^2 \pi} \mathbf{d}L - 2\rho \frac{L}{r^3 \pi} \mathbf{d}r \tag{2}$$

Using Equation (1) and Equation (2) the relative change in resistance of a carbon fibre (d*R*/*R*0) can be expressed as:

$$
\left(\frac{\text{d}R}{R\_0}\right) = \frac{\text{d}\rho}{\rho} + \varepsilon (1 + 2\nu) = k\varepsilon \tag{3}
$$

$$
\text{with } \varepsilon = \frac{dL}{L} \text{ and } \nu = -\frac{dr/r}{dL/L}
$$

For some applications of CFSs it can be useful to split the strain sensitivity *k* into the longitudinal strain sensitivity *kl* and the transverse strain sensitivity *kt*. The relative change

The strain sensitivity *k* of a T300B 1K fibre was determined as *k* = 1.71 for a corresponding Poisson ratio *ν* of 0.28. The sensor fibre exhibits a longitudinal strain sensitivity *kl* in the range of 1.72 to 1.78 and a transverse strain sensitivity *kt* in the range of 0.37 to 0.41. The piezoresistivity of the ex-PAN fibre is linear up to a strain level of approximately 6000 *μ*m/m [1, 6]. Problems may occur at the metallized fibre endings. In order to avoid any influence of the electrical connections the strain level at the fibre endings should not exceed a level of

This can be realized by using special tabs which exhibit a higher stiffness in the regions of the metallic connections. An example of such load relieving tabs is given in Figure 5. The lay-up of the tabs ensures a four times smaller strain level in the region of the electrical connections

5 ]

Figure 6 shows the excellent linear piezoresistive behaviour of the ex-PAN fibre T300B 1K up to a strain level of 6000 *μ*m/m (loading and unloading). Bending tests were performed to investigate the compression behaviour of CFSs. These investigations are not completed. First results show that the linearity of the signal depends significant on the carrier material.

= *klε<sup>l</sup>* + *ktε<sup>t</sup>* (4)

Carbon Fibre Sensor: Theory and Application 361

d*R R* 

compared to the strain level which occurs in the testing area.

**Figure 5.** CFS patch with load relieving tabs

Lay-up in the regions of the metallized fibre endings: [0◦

Lay-up in the testing area: [0◦]

in resistance is then given by:

2500 *μ*m/m.

The term d*ρ*/*ρ* denotes the piezoresistive effect (material effect) and the term *ε*(1 + 2*ν*) represents the geometric effects. The strain sensitivity *k* covers both effects. It should be noted that the strain sensitivity *k* depends on the effective Poisson ratio *ν* 3. Therefore, the strain sensitivity *k* must be defined for a corresponding Poisson ratio4.

<sup>3</sup> The effective Poisson ratio *ν* depends on the Poisson ratio of the sensor fibre *ν<sup>f</sup>* , the Poisson ratio of the sensor patch *<sup>ν</sup><sup>p</sup>* and the strain ratio <sup>−</sup>*εy*/*ε<sup>x</sup>* of the structure. <sup>4</sup> Conventional strain gauges exhibits the same behaviour. The strain sensitivity of strain gauges is usually defined for

a corresponding Poisson ratio *ν* = 0.285 (steel).

For some applications of CFSs it can be useful to split the strain sensitivity *k* into the longitudinal strain sensitivity *kl* and the transverse strain sensitivity *kt*. The relative change in resistance is then given by:

4 Will-be-set-by-IN-TECH

IM Fibres HM Fibres

100 200 300 400 500 600 700 800 900 1000

**Figure 4.** Correlation between the specific resistance *ρ* and the Young's modulus *E* of different ex-PAN

where *ρ* is the specific resistivity, *L* the length and *r* the radius of the fibre. The total differential

<sup>d</sup>*<sup>r</sup>* <sup>=</sup> *<sup>L</sup> r*2*π*

Using Equation (1) and Equation (2) the relative change in resistance of a carbon fibre (d*R*/*R*0)

The term d*ρ*/*ρ* denotes the piezoresistive effect (material effect) and the term *ε*(1 + 2*ν*) represents the geometric effects. The strain sensitivity *k* covers both effects. It should be noted that the strain sensitivity *k* depends on the effective Poisson ratio *ν* 3. Therefore, the

<sup>3</sup> The effective Poisson ratio *ν* depends on the Poisson ratio of the sensor fibre *ν<sup>f</sup>* , the Poisson ratio of the sensor patch *<sup>ν</sup><sup>p</sup>* and the strain ratio <sup>−</sup>*εy*/*ε<sup>x</sup>* of the structure. <sup>4</sup> Conventional strain gauges exhibits the same behaviour. The strain sensitivity of strain gauges is usually defined for

*<sup>L</sup>* and *<sup>ν</sup>* <sup>=</sup> <sup>−</sup> *dr*/*<sup>r</sup>*

d*ρ* + *ρ*

*dL*/*L*

1 *r*2*π*

d*L* − 2*ρ*

+ *ε*(1 + 2*ν*) = *kε* (3)

*L r*3*π*

d*r* (2)

*∂R ∂r*

of *R* = *f*(*ρ*, *L*,*r*) is then yielded by the following Equation (2).

*∂R <sup>∂</sup><sup>L</sup>* <sup>d</sup>*<sup>L</sup>* <sup>+</sup>

d*R R*0 <sup>=</sup> <sup>d</sup>*<sup>ρ</sup> ρ*

with *<sup>ε</sup>* <sup>=</sup> *dL*

strain sensitivity *k* must be defined for a corresponding Poisson ratio4.

*∂ρ* <sup>d</sup>*<sup>ρ</sup>* <sup>+</sup>

Young's modulus *E* [GPa]

ex-PAN fibres ex-pitch fibres

and ex-pitch carbon fibres

can be expressed as:

Specific resistivity

*ρ* [μΩm]

T300B

HT Fibres

HT: High tenacity IM: Intermedite modulus HM: High modulus

<sup>d</sup>*<sup>R</sup>* <sup>=</sup> *<sup>∂</sup><sup>R</sup>*

a corresponding Poisson ratio *ν* = 0.285 (steel).

$$\left(\frac{\mathrm{d}R}{R}\right) = k\_l \varepsilon\_l + k\_l \varepsilon\_l \tag{4}$$

The strain sensitivity *k* of a T300B 1K fibre was determined as *k* = 1.71 for a corresponding Poisson ratio *ν* of 0.28. The sensor fibre exhibits a longitudinal strain sensitivity *kl* in the range of 1.72 to 1.78 and a transverse strain sensitivity *kt* in the range of 0.37 to 0.41. The piezoresistivity of the ex-PAN fibre is linear up to a strain level of approximately 6000 *μ*m/m [1, 6]. Problems may occur at the metallized fibre endings. In order to avoid any influence of the electrical connections the strain level at the fibre endings should not exceed a level of 2500 *μ*m/m.

This can be realized by using special tabs which exhibit a higher stiffness in the regions of the metallic connections. An example of such load relieving tabs is given in Figure 5. The lay-up of the tabs ensures a four times smaller strain level in the region of the electrical connections compared to the strain level which occurs in the testing area.

**Figure 5.** CFS patch with load relieving tabs Lay-up in the testing area: [0◦] Lay-up in the regions of the metallized fibre endings: [0◦ 5 ]

Figure 6 shows the excellent linear piezoresistive behaviour of the ex-PAN fibre T300B 1K up to a strain level of 6000 *μ*m/m (loading and unloading). Bending tests were performed to investigate the compression behaviour of CFSs. These investigations are not completed. First results show that the linearity of the signal depends significant on the carrier material.

Ex-pitch fibres show a nonlinear piezoresistive behaviour.

*(ΔR*/*R0*) (carbon fibre sensor)

*R1* … *R4*: resistances, bridge arms *Vs*: bridge supply voltage *Vout*: bridge output voltage

Carbon Fibre Sensor: Theory and Application 363

*V RRRR V RRRR*

1 4

<sup>−</sup> <sup>Δ</sup>*R*2,*therm R*2

*R1 R4*

*Vout*

*R2 R3*

(b) Full bridge circuit

*ε*(*x*) d*x* (6)

*out s*

1234 1234

(5)

*V*

*s*

§ · '''' ¨ ¸ © ¹

*R1 R4*

2

*Vout*

1 4

*V*

*s*

temperature effects (thermal dependency of the specific resistance and thermal expansion) if the thermal conditions of the connected CFSs are identical. In the case of a half bridge circuit

> Δ*R*1,*mech* + Δ*R*1,*therm R*1

bridge can be found in classical textbooks on strain gauge techniques (e.g. [5, 13])

*V*

**Figure 8.** Half bridge and full bridge configuration of the Wheatstone bridge

**4. Integral strain measurement of the carbon fibre sensor**

 Δ*R R*0 = *k* 1 *L L* 0

Equation (3) describes the relative change in electrical resistance (Δ*R*/*R*0) of a carbon fibre sensor due to an applied elastic strain *ε*. It is important to understand that a CFS measures the

strain integrally along its whole fibre length. Thus, Equation (3) can be written as:

*s*

Equation (5) shows that the thermal effect is compensated by the mechanically unloaded carbon fibre sensor (*R*2). Detailed information about the principle and use of the Wheatstone

*R2 R3*

3

with one active CFS (*R*1) the output voltage *Vout* is given by:

*Vout* <sup>=</sup> *Vs* 4

**Figure 7.** General Wheatstone bridge circuit

*R1 R4*

*Vout*

*R2 R3*

(a) Half bridge circuit

**Figure 6.** Characterization of the linear piezoresistivity up to a strain level of 6000 *μ*m/m (loading and unloading) by means of a CFS patch with load relieving tabs at the endings Sensor fibre: T300B 1K (ex-PAN fibre) Lay-up in the testing area: [0◦ 8 ] Lay-up of the load relieving tabs: [±45◦, 0◦ <sup>3</sup> ]*sym*

## **3. The Wheatstone bridge**

The change in resistance of a CFS due to an applied strain is usually small. The Wheatstone bridge is an electrical circuit which allows the determination of very small changes in electrical resistance with great accuracy. Furthermore, the Wheatstone bridge minimizes the high influence of temperature changes on the CFS signal. The measurement circuit, illustrated in Figure 7, consists of four resistances, a supply voltage and the output voltage of the bridge. The relative change in resistance can be determined by the ratio of output voltage to input voltage *Vout*/*Vs*. There are two configurations of the Wheatstone bridge which are of special importance for the use of CFSs. These configurations of the Wheatstone bridge are known as "half bridge" configuration and "full bridge" configuration.

In the case of a half bridge circuit (Figure 8(a)), the bridge is formed by two CFSs (*R*<sup>1</sup> and *R*2) and two completion resistors (*R*<sup>3</sup> and *R*4). The full bridge configuration (Figure 8(b)) is formed by four CFSs and needs no additional resistors. Both circuits will enable a compensation of

*R1* … *R4*: resistances, bridge arms *Vs*: bridge supply voltage *Vout*: bridge output voltage

$$\frac{V\_{out}}{V\_s} = \frac{1}{4} \left( \frac{\Delta R\_1}{R\_1} - \frac{\Delta R\_2}{R\_2} + \frac{\Delta R\_3}{R\_3} - \frac{\Delta R\_4}{R\_4} \right)$$

**Figure 7.** General Wheatstone bridge circuit

6 Will-be-set-by-IN-TECH

0 0.001 0.002 0.003 0.004 0.005 0.006 0.007 0.008

*(ΔR*/*R0*) (carbon fibre sensor)

0 500 1000 1500 2000 2500 3000 3500 4000 4500 5000 5500 6000

**Figure 6.** Characterization of the linear piezoresistivity up to a strain level of 6000 *μ*m/m (loading and

The change in resistance of a CFS due to an applied strain is usually small. The Wheatstone bridge is an electrical circuit which allows the determination of very small changes in electrical resistance with great accuracy. Furthermore, the Wheatstone bridge minimizes the high influence of temperature changes on the CFS signal. The measurement circuit, illustrated in Figure 7, consists of four resistances, a supply voltage and the output voltage of the bridge. The relative change in resistance can be determined by the ratio of output voltage to input voltage *Vout*/*Vs*. There are two configurations of the Wheatstone bridge which are of special importance for the use of CFSs. These configurations of the Wheatstone bridge are known as

In the case of a half bridge circuit (Figure 8(a)), the bridge is formed by two CFSs (*R*<sup>1</sup> and *R*2) and two completion resistors (*R*<sup>3</sup> and *R*4). The full bridge configuration (Figure 8(b)) is formed by four CFSs and needs no additional resistors. Both circuits will enable a compensation of

unloading) by means of a CFS patch with load relieving tabs at the endings

<sup>3</sup> ]*sym*

8 ]

"half bridge" configuration and "full bridge" configuration.

Strain [μm/m] (Strain gauge)

Strain gauge

Carbon fibre sensor

Ex-pitch fibres show a nonlinear piezoresistive behaviour.

0

Sensor fibre: T300B 1K (ex-PAN fibre) Lay-up in the testing area: [0◦

**3. The Wheatstone bridge**

Lay-up of the load relieving tabs: [±45◦, 0◦

50

100

150

Stress

*σ* [MPa]

200

250

300

temperature effects (thermal dependency of the specific resistance and thermal expansion) if the thermal conditions of the connected CFSs are identical. In the case of a half bridge circuit with one active CFS (*R*1) the output voltage *Vout* is given by:

$$V\_{out} = \frac{V\_s}{4} \left( \frac{\Delta R\_{1,mech} + \Delta R\_{1,therm}}{R\_1} - \frac{\Delta R\_{2,therm}}{R\_2} \right) \tag{5}$$

Equation (5) shows that the thermal effect is compensated by the mechanically unloaded carbon fibre sensor (*R*2). Detailed information about the principle and use of the Wheatstone bridge can be found in classical textbooks on strain gauge techniques (e.g. [5, 13])

(a) Half bridge circuit

**Figure 8.** Half bridge and full bridge configuration of the Wheatstone bridge

#### **4. Integral strain measurement of the carbon fibre sensor**

Equation (3) describes the relative change in electrical resistance (Δ*R*/*R*0) of a carbon fibre sensor due to an applied elastic strain *ε*. It is important to understand that a CFS measures the strain integrally along its whole fibre length. Thus, Equation (3) can be written as:

$$
\varepsilon \left( \frac{\Delta R}{R\_0} \right) = k \frac{1}{L} \int\_0^L \varepsilon(\mathbf{x}) \, \mathbf{dx} \tag{6}
$$

Equation (6) shows that a CFS measures the displacement between the terminal points of the sensor fibre.

$$
\left(\frac{\Delta R}{R\_0}\right)\frac{L}{k} = \int\_0^L \varepsilon(\mathbf{x}) \, \mathbf{dx} = \left[\mu(\mathbf{x} = L) - \mu(\mathbf{x} = 0)\right] \tag{7}
$$

This integral strain measurement of CFSs in accordance to Equation (7) can be used to create carbon fibre sensor meshes (CFS meshes). Such a CFS mesh allows the determination of the two dimensional (2D) state of strain and state of deformation of a whole structure or larger areas of a structure.

## **5. Carbon fibre sensor meshes**

The strain and deformation analysis by means of CFS meshes are based on linear or higher order displacement approximations. The displacement functions depend on the used element type such as 3-node triangle elements, 6-node triangle elements or quadrilateral elements. The basic theory of strain analysis with CFS meshes using 3-node triangle elements with a linear displacement approximation is presented below.

A triangular CFS element defined by its vertices 1, 2, 3 and its local coordinate system is given in Figure 9.

**Figure 9.** Triangle CFS element with 3 nodes

triangle can be found in classical books on the theory of finite element analysis (e.g. [16]). The

*δy*

Considering the local coordinate system (*u*<sup>1</sup> = 0, *v*<sup>1</sup> = 0, *v*<sup>2</sup> = 0) the strains within the triangle

In consequence of the linear displacement approximation the strains are independent of the coordinates (*x* and *y*) and thus constant within the element. The unknown displacements *u*2, *u*<sup>3</sup> and *v*<sup>3</sup> of the vertex 2 and 3 can be determined by the signals of the carbon fibre sensors. In order to verify this linear approach an experimental investigation of a CFS mesh applied on a 1000 mm x 1000 mm x 5 mm PMMA plate was performed. The simply supported plate was loaded with a single static force at the center. In addition to the experiment a finite element analysis (FEA) was performed. In [9] the results of this experiment and of the corresponding finite element simulations are presented in detail 5. Figure 10 shows the PMMA plate and the

**Figure 10.** Carbon fibre sensor mesh applied ona1mx1m PMMA plate. Each sensor has a length of

Figure 11 shows the determined strain *ε<sup>x</sup>* for each element of the mesh. There was a good correlation between the measured and the calculated strain levels. The accuracy was in the

The results of the performed investigation show that CFS meshes are a reliable instrument to

The principle strains (strain level and direction) are of particular interest in case of structures made of composite materials. For example, tailored fibre placement (TFP) is an advanced textile manufacturing process for CFRP structures in which the carbon fibre rovings are placed

<sup>5</sup> A quadratic displacement approach for a 3-node triangle is also presented and verified in [9]. However, the quadratic displacement approach of a 3-node triangle requires additional strain gauges at the nodes to determine the 12

determine the strain fields and principle strains of lightweight structures.

*y*3

; *<sup>γ</sup>xy* <sup>=</sup> *<sup>δ</sup><sup>u</sup>*

; *<sup>γ</sup>xy* <sup>=</sup> *<sup>x</sup>*2*u*<sup>3</sup> <sup>−</sup> *<sup>x</sup>*3*u*<sup>2</sup>

*δy* + *δv*

*x*2*y*<sup>3</sup>

*<sup>δ</sup><sup>x</sup>* (10)

Carbon Fibre Sensor: Theory and Application 365

(11)

; *<sup>ε</sup><sup>y</sup>* <sup>=</sup> *<sup>δ</sup><sup>v</sup>*

; *<sup>ε</sup><sup>y</sup>* <sup>=</sup> *<sup>v</sup>*<sup>3</sup>

engineering strains *εx*, *ε<sup>y</sup>* and *γxy* are defined by:

can be calculated by:

applied CFS mesh.


300mm. [9]

range of ± 5%.

 *--*


 *-* -*-*

 

 *--*

 

 

  -

*-*

unknown coefficients of the shape function.

 

*<sup>ε</sup><sup>x</sup>* <sup>=</sup> *<sup>δ</sup><sup>u</sup> δx*

*<sup>ε</sup><sup>x</sup>* <sup>=</sup> *<sup>u</sup>*<sup>2</sup> *x*2

(a) Definition local coordinate system (b) CFS element applied on aluminium

The displacement *u*(*x*, *y*) and *v*(*x*, *y*) of an inner point *P* can be determined by the displacements of the vertex in using a displacement function.

Assuming a linear displacement function the displacement *u*(*x*, *y*) and *v*(*x*, *y*) within the element can be calculated in accordance to Equation (8) and Equation (9).

$$
\mu(\mathbf{x}, \mathbf{y}) = \mathbf{N}\_1 \boldsymbol{\mu}\_1 + \mathbf{N}\_2 \boldsymbol{\mu}\_2 + \mathbf{N}\_3 \boldsymbol{\mu}\_3 \tag{8}
$$

$$v(x, y) = N\_1 v\_1 + N\_2 v\_2 + N\_3 v\_3 \tag{9}$$

Hereby *ui* and *vi* denote the displacements of the vertex 1, 2, 3 in the *x*- and *y*-direction while *Ni* represents the shape functions of the element. The shape functions *Ni* of a 3-node triangle can be found in classical books on the theory of finite element analysis (e.g. [16]). The engineering strains *εx*, *ε<sup>y</sup>* and *γxy* are defined by:

8 Will-be-set-by-IN-TECH

Equation (6) shows that a CFS measures the displacement between the terminal points of the

This integral strain measurement of CFSs in accordance to Equation (7) can be used to create carbon fibre sensor meshes (CFS meshes). Such a CFS mesh allows the determination of the two dimensional (2D) state of strain and state of deformation of a whole structure or larger

The strain and deformation analysis by means of CFS meshes are based on linear or higher order displacement approximations. The displacement functions depend on the used element type such as 3-node triangle elements, 6-node triangle elements or quadrilateral elements. The basic theory of strain analysis with CFS meshes using 3-node triangle elements with a linear

A triangular CFS element defined by its vertices 1, 2, 3 and its local coordinate system is given

*x*

The displacement *u*(*x*, *y*) and *v*(*x*, *y*) of an inner point *P* can be determined by the

Assuming a linear displacement function the displacement *u*(*x*, *y*) and *v*(*x*, *y*) within the

Hereby *ui* and *vi* denote the displacements of the vertex 1, 2, 3 in the *x*- and *y*-direction while *Ni* represents the shape functions of the element. The shape functions *Ni* of a 3-node

*u*(*x*, *y*) = *N*1*u*<sup>1</sup> + *N*2*u*<sup>2</sup> + *N*3*u*<sup>3</sup> (8) *v*(*x*, *y*) = *N*1*v*<sup>1</sup> + *N*2*v*<sup>2</sup> + *N*3*v*<sup>3</sup> (9)

(a) Definition local coordinate system (b) CFS element applied on aluminium

*ε*(*x*) d*x* = [*u*(*x* = *L*) − *u*(*x* = 0)] (7)

sensor fibre.

in Figure 9.

*y*

areas of a structure.

**5. Carbon fibre sensor meshes**

 Δ*R R*0

displacement approximation is presented below.

*c c´*

3 *u*3 *v*3

*P ´ u v*

1´ 1 2 2´

*b*

**Figure 9.** Triangle CFS element with 3 nodes

*P*

*b´*

*a*

displacements of the vertex in using a displacement function.

element can be calculated in accordance to Equation (8) and Equation (9).

3´

*a´*

*u*2

 *L <sup>k</sup>* <sup>=</sup>  *L* 0

$$
\varepsilon\_{\mathbf{x}} = \frac{\delta u}{\delta \mathbf{x}}; \qquad \varepsilon\_{\mathbf{y}} = \frac{\delta v}{\delta y}; \qquad \gamma\_{\mathbf{xy}} = \frac{\delta u}{\delta y} + \frac{\delta v}{\delta \mathbf{x}} \tag{10}
$$

Considering the local coordinate system (*u*<sup>1</sup> = 0, *v*<sup>1</sup> = 0, *v*<sup>2</sup> = 0) the strains within the triangle can be calculated by:

$$
\varepsilon\_{\mathbf{x}} = \frac{\mathfrak{u}\_2}{\mathfrak{x}\_2}; \qquad \varepsilon\_{\mathbf{y}} = \frac{\mathfrak{v}\_3}{\mathfrak{y}\_3}; \qquad \gamma\_{\mathbf{xy}} = \frac{\mathfrak{x}\_2 \mathfrak{u}\_3 - \mathfrak{x}\_3 \mathfrak{u}\_2}{\mathfrak{x}\_2 \mathfrak{y}\_3} \tag{11}
$$

In consequence of the linear displacement approximation the strains are independent of the coordinates (*x* and *y*) and thus constant within the element. The unknown displacements *u*2, *u*<sup>3</sup> and *v*<sup>3</sup> of the vertex 2 and 3 can be determined by the signals of the carbon fibre sensors.

In order to verify this linear approach an experimental investigation of a CFS mesh applied on a 1000 mm x 1000 mm x 5 mm PMMA plate was performed. The simply supported plate was loaded with a single static force at the center. In addition to the experiment a finite element analysis (FEA) was performed. In [9] the results of this experiment and of the corresponding finite element simulations are presented in detail 5. Figure 10 shows the PMMA plate and the applied CFS mesh.

**Figure 10.** Carbon fibre sensor mesh applied ona1mx1m PMMA plate. Each sensor has a length of 300mm. [9]

Figure 11 shows the determined strain *ε<sup>x</sup>* for each element of the mesh. There was a good correlation between the measured and the calculated strain levels. The accuracy was in the range of ± 5%.

The results of the performed investigation show that CFS meshes are a reliable instrument to determine the strain fields and principle strains of lightweight structures.

The principle strains (strain level and direction) are of particular interest in case of structures made of composite materials. For example, tailored fibre placement (TFP) is an advanced textile manufacturing process for CFRP structures in which the carbon fibre rovings are placed

<sup>5</sup> A quadratic displacement approach for a 3-node triangle is also presented and verified in [9]. However, the quadratic displacement approach of a 3-node triangle requires additional strain gauges at the nodes to determine the 12 unknown coefficients of the shape function.

Sensor fibre Matrix crack

**Figure 12.** Multidirectional reinforced GFRP laminate with two embedded CFSs. Transverse matrix

0 200 400 600 800 1000

Time [s]

**Figure 13.** Acoustic emission and CFS signals measured on an GFRP laminate under uniaxial tensile

Furthermore, a good correlation between the sensor signal (Δ*R*/*R*0) and the crack density can be observed. After having reached a crack density of 0.8 mm−<sup>1</sup> the signals of the embedded carbon fibre sensors increase disproportionately. The analytical approach of Garret and Bailey [4, 11, 12] and a FEA were applied to calculate the reduction of the stiffness of the laminate. Müller showed that the global stiffness loss of the laminate due to the matrix cracking can be measured by means of the CFS. However, at high strain levels (*>* 70% of *εultimate*) there

Figure 13 shows the correlation between the crack density, the CFS signals, the acoustic emission energy (AE-energy), the strain level measured by a strain gauge and the according stress level. It can be seen that the matrix crack initiation causes first AE-signals and a change

0.0

0.1

0.2

0.3

0.4

0.5

normalised strain gauge signal [20.000 μm/m]

normalised CFS signal

normalised crack density [1,1 mm-1]

ΔR/R [ 0,04]

0.6

0.7

0.8

0.9

1.0

Carbon Fibre Sensor: Theory and Application 367

0°

Stress AE-energy Crack density Strain gauge CFS 1 CFS 2 CFS 3

90°

cracking will affect the sensor signal.

<sup>2</sup> , 0◦, 90◦ 2 ]

of the slope of the CFS signals.

0

<sup>5</sup> , 0◦, 90◦

<sup>5</sup> , 0◦]

load [10] Lay-up: [0◦, 90◦

50

100

150

Stress [MPa], AE-energy [pJ]

200

250

Lay-up: [90◦

in accordance to the direction of principal stresses.

The finite element simulation is a powerful tool to analyse the stress fields and principle directions of lightweight structures. At the design and optimization processes the FEA is almost the only way to evaluate the structural load. However, there is a lack of techniques to review the results of the FEA. CFS meshes offer a high potential to verify the results of the finite element analysis.

## **6. Micro crack detection**

A major failure mode of multidirectional reinforced laminates is transverse matrix cracking. Matrix cracks will reduce the effective stiffness of the laminate and will result in local stress concentrations at the crack tip. Furthermore, interlaminar crack growth and local delamination can occur. Due to its integral strain measurement method the CFS has a high potential to detect matrix crack initiation and monitor crack growth. Figure 12 shows a thin GFRP laminate (Lay-up: [90◦ 2, 0◦, 90◦ <sup>2</sup> ]) which has two embedded CFSs. Matrix cracks along the CFS will affect the sensor signal which will give a clear indication of the crack density. A study was performed to investigate the influence of cracks on the sensor signal [10]. The study was performed on the GFRP laminate [0◦, 90◦ 5, 0◦, 90◦ <sup>5</sup>, 0◦]. Three CFSs were embedded in the mid-plane 0◦-layer. At a strain level higher than 3000 *μ*m/m matrix cracks appeared in the 90◦-layers. The following techniques were applied to characterize the influence of damages on the sensor signal:


10 Will-be-set-by-IN-TECH



<sup>2</sup> ]) which has two embedded CFSs. Matrix cracks along

<sup>5</sup>, 0◦]. Three CFSs were embedded in the


The finite element simulation is a powerful tool to analyse the stress fields and principle directions of lightweight structures. At the design and optimization processes the FEA is almost the only way to evaluate the structural load. However, there is a lack of techniques to review the results of the FEA. CFS meshes offer a high potential to verify the results of the

A major failure mode of multidirectional reinforced laminates is transverse matrix cracking. Matrix cracks will reduce the effective stiffness of the laminate and will result in local stress concentrations at the crack tip. Furthermore, interlaminar crack growth and local delamination can occur. Due to its integral strain measurement method the CFS has a high potential to detect matrix crack initiation and monitor crack growth. Figure 12 shows a thin

the CFS will affect the sensor signal which will give a clear indication of the crack density. A study was performed to investigate the influence of cracks on the sensor signal [10]. The study

mid-plane 0◦-layer. At a strain level higher than 3000 *μ*m/m matrix cracks appeared in the 90◦-layers. The following techniques were applied to characterize the influence of damages

• Acoustic emission analysis in combination with pattern recognition technique

5, 0◦, 90◦




> -

> -


**Figure 11.** Strain *ε<sup>x</sup>* measured by the carbon fibre sensor mesh

2, 0◦, 90◦

in accordance to the direction of principal stresses.

finite element analysis.

**6. Micro crack detection**

GFRP laminate (Lay-up: [90◦

• Microscopy and micrographs

• Analytical calculations • Finite element analysis

on the sensor signal:

was performed on the GFRP laminate [0◦, 90◦

**Figure 12.** Multidirectional reinforced GFRP laminate with two embedded CFSs. Transverse matrix cracking will affect the sensor signal. Lay-up: [90◦ <sup>2</sup> , 0◦, 90◦ 2 ]

Figure 13 shows the correlation between the crack density, the CFS signals, the acoustic emission energy (AE-energy), the strain level measured by a strain gauge and the according stress level. It can be seen that the matrix crack initiation causes first AE-signals and a change of the slope of the CFS signals.

**Figure 13.** Acoustic emission and CFS signals measured on an GFRP laminate under uniaxial tensile load [10] Lay-up: [0◦, 90◦ <sup>5</sup> , 0◦, 90◦ <sup>5</sup> , 0◦]

Furthermore, a good correlation between the sensor signal (Δ*R*/*R*0) and the crack density can be observed. After having reached a crack density of 0.8 mm−<sup>1</sup> the signals of the embedded carbon fibre sensors increase disproportionately. The analytical approach of Garret and Bailey [4, 11, 12] and a FEA were applied to calculate the reduction of the stiffness of the laminate. Müller showed that the global stiffness loss of the laminate due to the matrix cracking can be measured by means of the CFS. However, at high strain levels (*>* 70% of *εultimate*) there is a strong influence of high local stresses at the crack tip on the CFS signal. These stress concentrations may result in filament breakage and in extremely high signal levels.

such a way that readily detectable damages will be repaired before damage growth can affect the fatigue strength of the structure. The influence of undetectable damages is covered by the so called barely visible impact damage (BVID) which defines the damage that establishes the strength values to be used in analysis to demonstrate compliance with the load requirements. One method to determine the influence of the BVID on the mechanical performance is the compression after impact test procedure (CAI-test procedure, i.e. Boeing BSS 7260). A 4 mm thick quasi-isotropic test specimen (150 x 100 mm) is damaged by a dropped weight impact testing machine. An impact level of about 3 J/mm will cause the BVID. This means that only a small remaining indentation is visible on the surface of the specimen, but delamination may be found inside. The strength of the damaged specimen is reduced by 10 to 20% compared to the undamaged material. This shows that in many cases the exploitation of material performance is limited, since the skin thicknesses of a composite structure are designed to absorb an impact. For aircraft structures health monitoring systems have an extremely high potential to improve the efficiency of composite structures. Based on a monitoring system the material design values can be increased and the inspection intervals can be enlarged. Both aspects can result in a weight reduction of the structure up to 10%. A preliminary study was performed to investigate the use of CFSs as a sensor system to detect the BVID. The CAI specimen was used

Carbon Fibre Sensor: Theory and Application 369

**Figure 15.** Compression after impact (CAI)-specimen with integrated CFS mesh to detect damages

• Offline measurements, comparison of the resistivity before and after the impact

The distance between the CFSs varied from 30 to 100 mm. Three methods were investigated

It has been shown that all three procedures are suitable to detect impact damages. A distance of 50 mm between the CFSs is necessary to detect even small damages below the

to integrate a rectangular CFS mesh (Figure 15 and Figure 16).

below the barely visible impact damage level (BVID)

• Online measurements of the resistivity during the impact test

• Active thermography, CFSs used as heating element

to detect the impact damage:

Based on this result CFSs can be used for damage monitoring and for the prediction of the lifetime of damaged structures if the damage level can be characterized by stiffness loss. Figure 14 shows the cyclic loading of a laminate to measure the stiffness loss and to determine Ladeveze's material parameters [8]. Based on this calibration the lifetime of a structure, e.g. pressure vessel, can be predicted.

**Figure 14.** Damage measurement and determination of damage variables like the energy release rate Material: GFRP, EG/913 Lay-up: [0◦, 90◦ <sup>5</sup> , 0◦, 90◦ <sup>5</sup> , 0◦]

## **7. Impact and delamination detection**

An impact loading can cause small damages inside the composite material which may not be found by visible inspection. One major concern is delamination damages or the disbonding of interfaces. These damages result in sublaminates having lower buckling resistance and compression strength. Although a small delamination-damage does not necessarily constitute failure, the damaged area may undergo a time-dependent growth and may attend a critical size.

The principles for achieving damage tolerant primary composite structures were established by the aircraft companies [14]. Maintenance intervals and inspection plans are determined in such a way that readily detectable damages will be repaired before damage growth can affect the fatigue strength of the structure. The influence of undetectable damages is covered by the so called barely visible impact damage (BVID) which defines the damage that establishes the strength values to be used in analysis to demonstrate compliance with the load requirements. One method to determine the influence of the BVID on the mechanical performance is the compression after impact test procedure (CAI-test procedure, i.e. Boeing BSS 7260). A 4 mm thick quasi-isotropic test specimen (150 x 100 mm) is damaged by a dropped weight impact testing machine. An impact level of about 3 J/mm will cause the BVID. This means that only a small remaining indentation is visible on the surface of the specimen, but delamination may be found inside. The strength of the damaged specimen is reduced by 10 to 20% compared to the undamaged material. This shows that in many cases the exploitation of material performance is limited, since the skin thicknesses of a composite structure are designed to absorb an impact.

12 Will-be-set-by-IN-TECH

is a strong influence of high local stresses at the crack tip on the CFS signal. These stress

Based on this result CFSs can be used for damage monitoring and for the prediction of the lifetime of damaged structures if the damage level can be characterized by stiffness loss. Figure 14 shows the cyclic loading of a laminate to measure the stiffness loss and to determine Ladeveze's material parameters [8]. Based on this calibration the lifetime of a structure, e.g.

0 2000 4000 6000 8000 10000 12000 14000 16000

Load step 1 (σ ≈ 70 N/mm²) Load step 2 (σ ≈ 90 N/mm²) Load step 3 (σ ≈ 110 N/mm²) Load step 4 (σ ≈ 120 N/mm²) Load step 5 (σ ≈ 150 N/mm²)

Strain signal of the carbon-fibre sensor [μm/m]

**Figure 14.** Damage measurement and determination of damage variables like the energy release rate

An impact loading can cause small damages inside the composite material which may not be found by visible inspection. One major concern is delamination damages or the disbonding of interfaces. These damages result in sublaminates having lower buckling resistance and compression strength. Although a small delamination-damage does not necessarily constitute failure, the damaged area may undergo a time-dependent growth and may attend a critical

The principles for achieving damage tolerant primary composite structures were established by the aircraft companies [14]. Maintenance intervals and inspection plans are determined in

concentrations may result in filament breakage and in extremely high signal levels.

pressure vessel, can be predicted.

0

Material: GFRP, EG/913 Lay-up: [0◦, 90◦

size.

<sup>5</sup> , 0◦, 90◦

<sup>5</sup> , 0◦]

**7. Impact and delamination detection**

20

40

60

Stress

*σ* [N/mm²]

80

100

120

140

160

For aircraft structures health monitoring systems have an extremely high potential to improve the efficiency of composite structures. Based on a monitoring system the material design values can be increased and the inspection intervals can be enlarged. Both aspects can result in a weight reduction of the structure up to 10%. A preliminary study was performed to investigate the use of CFSs as a sensor system to detect the BVID. The CAI specimen was used to integrate a rectangular CFS mesh (Figure 15 and Figure 16).

**Figure 15.** Compression after impact (CAI)-specimen with integrated CFS mesh to detect damages below the barely visible impact damage level (BVID)

The distance between the CFSs varied from 30 to 100 mm. Three methods were investigated to detect the impact damage:


It has been shown that all three procedures are suitable to detect impact damages. A distance of 50 mm between the CFSs is necessary to detect even small damages below the

#### 14 Will-be-set-by-IN-TECH 370 Composites and Their Applications Carbon Fibre Sensor: Theory and Application <sup>15</sup>

BVID. In a second step the use of CFSs will be investigated to detect debonding of skin and stringer. A health monitoring system for a complex aircraft structure will be based on several technologies like ultrasonic inspection sensors and strain sensors. The CFS technology will complement the established sensors due to its specific and simple integral measurement principle.

**Figure 16.** Compression after impact (CAI)-specimen with integrated CFS mesh. The CFSs are used as heating element for active thermography. A small delamination damage is visible (BVID)

## **8. Application**

CFSs offer a high potential to be used as a sensor element for composite materials for stress analysis, damage detection and the monitoring of manufacturing processes. Two industrial applications have been selected to demonstrate this.

## **8.1. Tabletop of a CT-Scanner**

Carbon fibre reinforced plastics (CFRP) are used for tabletops of computer tomography (CT) scanners, since CFRP fulfills the X-Ray transparency which is necessary to get the picture quality sufficient for medical diagnosis.

CFSs can be embedded in the tabletop of a CT scanner to measure its deflection. Based on the measured deflection the CT images can be readjusted to result in an improved medical attendance [7]. Figure 17 shows the tabletop of a CT scanner with ten u-shaped CFSs applied. For this application u-shaped CFSs are used to avoid that any metal wiring is part of the scan plane for all operation positions. The lengths of the u-shaped CFSs vary from 250 to 1250 mm. The determination of the beam deflection is based on the integral strain measurement of CFSs (Equation (6)). Considering small deformations the relation between the elastic strain of the outer fibre *<sup>ε</sup>* and the beam deflection *<sup>v</sup>* is given by:

$$v = \iint v'' \mathbf{dx} \mathbf{dx} = \iint \frac{\hat{\mathbf{e}}}{\mathbf{e}\_y} \mathbf{dx} \mathbf{dx} \tag{12}$$

**Figure 17.** CT tabletop with u-shaped CFSs to measure the deflection. The metallic wiring is attached to

where *ey* denotes the distance from the neutral axis. Assuming a cantilever beam (see Figure 18) the slope *v*� of the beam can be determined directly by the signals of the CFSs. Assuming that the CFS starts at the clamping support (*x* = 0) the slope *v*� at the end of the

*key*

(*xn*) − *v*�

 *-*


 

 

 

2

(*xn*−1)

 Δ*R R i*

(13)

(*ln* − *ln*−1) (14)

Carbon Fibre Sensor: Theory and Application 371

(*<sup>x</sup>* <sup>=</sup> *li*) = *li*

(*xn*) <sup>−</sup> *<sup>v</sup>*�

*-*

*-*

*v*�

 *v*�

*i* ∑ *n*=1

> *--*

 

**Figure 18.** Side and top view of a cantilever beam with five u-shaped CFS

*-*

The deflection *y* of the beam can be calculated by numerical integration.

the clamping support.

applied CFS (*x* = *li*) becomes:

*v*(*x* = *li*) =

14 Will-be-set-by-IN-TECH

BVID. In a second step the use of CFSs will be investigated to detect debonding of skin and stringer. A health monitoring system for a complex aircraft structure will be based on several technologies like ultrasonic inspection sensors and strain sensors. The CFS technology will complement the established sensors due to its specific and simple integral measurement

**Figure 16.** Compression after impact (CAI)-specimen with integrated CFS mesh. The CFSs are used as

CFSs offer a high potential to be used as a sensor element for composite materials for stress analysis, damage detection and the monitoring of manufacturing processes. Two industrial

Carbon fibre reinforced plastics (CFRP) are used for tabletops of computer tomography (CT) scanners, since CFRP fulfills the X-Ray transparency which is necessary to get the picture

CFSs can be embedded in the tabletop of a CT scanner to measure its deflection. Based on the measured deflection the CT images can be readjusted to result in an improved medical attendance [7]. Figure 17 shows the tabletop of a CT scanner with ten u-shaped CFSs applied. For this application u-shaped CFSs are used to avoid that any metal wiring is part of the scan plane for all operation positions. The lengths of the u-shaped CFSs vary from 250 to 1250 mm. The determination of the beam deflection is based on the integral strain measurement of CFSs (Equation (6)). Considering small deformations the relation between the elastic strain of the

*v*d*x*d*x* =

 *<sup>ε</sup> ey*

d*x*d*x* (12)

heating element for active thermography. A small delamination damage is visible (BVID)

applications have been selected to demonstrate this.

outer fibre *<sup>ε</sup>* and the beam deflection *<sup>v</sup>* is given by:

*v* = 

**8.1. Tabletop of a CT-Scanner**

quality sufficient for medical diagnosis.

principle.

**8. Application**

**Figure 17.** CT tabletop with u-shaped CFSs to measure the deflection. The metallic wiring is attached to the clamping support.

where *ey* denotes the distance from the neutral axis. Assuming a cantilever beam (see Figure 18) the slope *v*� of the beam can be determined directly by the signals of the CFSs. Assuming that the CFS starts at the clamping support (*x* = 0) the slope *v*� at the end of the applied CFS (*x* = *li*) becomes:

$$v'(\mathbf{x} = l\_i) = \frac{l\_i}{k e\_{\mathcal{Y}}} \left(\frac{\Delta R}{R}\right)\_i \tag{13}$$

The deflection *y* of the beam can be calculated by numerical integration.

**Figure 18.** Side and top view of a cantilever beam with five u-shaped CFS

The index *i* denotes the number of CFSs applied. The quality of the approximation in accordance to Equation (14) depends on the complexity of the loading, the number of applied CFSs and the used sensor configuration.

There are two aspects for the use of CFSs for pressure vessels which can be easily integrated

Carbon Fibre Sensor: Theory and Application 373

• Monitoring of degradation processes due to fatigue or overloading of the radial fibre

For such an application a sensor patch with four CFSs connected in full-bridge configuration is particularly suitable, since the full-bridge circuit minimizes the influences of thermal effects and shows an improved long term stability of the signal. Figure 20 shows such a hoop

by means of the winding process:

reinforcement

• Determination of the pressure level of the vessel

wrapped vessel with an embedded CFS patch.

**Figure 20.** Hoop wrapped pressure vessel (type II vessel) with embedded CFSs

Experimental studies showed that the pressure of the vessel can be determined by using a CFS patch with a resolution of about 1 bar. A representative measurement of the performed test is shown in Figure 21. The pressure load of the vessel was increased stepwise up to a maximum pressure level of 100 bar. The subsequent pressure relief was performed in the same manner. Micro cracks in the CFRP layers of the pressure vessel may occur as a result of mechanical or thermal overloading. The failure of the matrix causes a loss of stiffness of the CFRP layers and reduces the global stiffness of the vessel. Depending on the crack density and the crack growth the lifetime of the structure will decrease. Based on the damage master curve of the

structure, an estimation of the remaining lifetime can be performed (see Figure 14).

In the case of the CT table (Figure 17) the deflection of the table can be determined with an accuracy of ±0.3 mm for different operation positions. Figure 19 shows a typical measurement. The operating position of the CT tabletop varies stepwise from 0 mm to 2000 mm and back to 0 mm. The weight of the used dummy is 100 kg and electrical half bridges are used for temperature compensation.

**Figure 19.** CFS signals of the CT table for a weight of 100 kg and different operation positions, ranging from 0 to 2000 mm

#### **8.2. Pressure vessels**

For thin walled assumptions the longitudinal stress *σ<sup>l</sup>* and hoop stress *σ<sup>r</sup>* in the cylindrical portion of a pressure vessel, away from the ends, are given by:

$$
\sigma\_l = \frac{pr}{2t} \tag{15}
$$

$$
\sigma\_{\overline{l}} = \frac{pr}{t} \tag{16}
$$

where *t* is the thickness and *r* is the radius of the vessel. The relation *σr*/*σ<sup>l</sup>* shows that the efficiency of pressure vessels can be increased if hoop wrapped vessels are used. A metal cylinder is reinforced by carbon fibres having a radial orientation (type II vessels). The strength of the vessel is increased remarkably.

There are two aspects for the use of CFSs for pressure vessels which can be easily integrated by means of the winding process:

• Determination of the pressure level of the vessel

16 Will-be-set-by-IN-TECH

The index *i* denotes the number of CFSs applied. The quality of the approximation in accordance to Equation (14) depends on the complexity of the loading, the number of applied

In the case of the CT table (Figure 17) the deflection of the table can be determined with an accuracy of ±0.3 mm for different operation positions. Figure 19 shows a typical measurement. The operating position of the CT tabletop varies stepwise from 0 mm to 2000 mm and back to 0 mm. The weight of the used dummy is 100 kg and electrical half

0 20 40 60 80 100 120 140

Time [s]

**Figure 19.** CFS signals of the CT table for a weight of 100 kg and different operation positions, ranging

For thin walled assumptions the longitudinal stress *σ<sup>l</sup>* and hoop stress *σ<sup>r</sup>* in the cylindrical

*<sup>σ</sup><sup>l</sup>* <sup>=</sup> *pr*

*<sup>σ</sup><sup>r</sup>* <sup>=</sup> *pr*

where *t* is the thickness and *r* is the radius of the vessel. The relation *σr*/*σ<sup>l</sup>* shows that the efficiency of pressure vessels can be increased if hoop wrapped vessels are used. A metal cylinder is reinforced by carbon fibres having a radial orientation (type II vessels). The

<sup>2</sup>*<sup>t</sup>* (15)

*<sup>t</sup>* (16)

CFSs and the used sensor configuration.


from 0 to 2000 mm

**8.2. Pressure vessels**






Strain signal [μm/m], (*k* = 2.0)




0

20

bridges are used for temperature compensation.

CFS\_1, l = 250 mm CFS\_2, l = 500 mm CFS\_3, l = 750 mm CFS\_4, l = 1000 mm CFS\_5, l = 1250 mm CFS\_6, l = 250 mm CFS\_7, l = 500 mm CFS\_8, l =750 mm CFS\_9, l = 1000 mm CFS\_10, l = 1250 mm

portion of a pressure vessel, away from the ends, are given by:

strength of the vessel is increased remarkably.

• Monitoring of degradation processes due to fatigue or overloading of the radial fibre reinforcement

For such an application a sensor patch with four CFSs connected in full-bridge configuration is particularly suitable, since the full-bridge circuit minimizes the influences of thermal effects and shows an improved long term stability of the signal. Figure 20 shows such a hoop wrapped vessel with an embedded CFS patch.

**Figure 20.** Hoop wrapped pressure vessel (type II vessel) with embedded CFSs

Experimental studies showed that the pressure of the vessel can be determined by using a CFS patch with a resolution of about 1 bar. A representative measurement of the performed test is shown in Figure 21. The pressure load of the vessel was increased stepwise up to a maximum pressure level of 100 bar. The subsequent pressure relief was performed in the same manner.

Micro cracks in the CFRP layers of the pressure vessel may occur as a result of mechanical or thermal overloading. The failure of the matrix causes a loss of stiffness of the CFRP layers and reduces the global stiffness of the vessel. Depending on the crack density and the crack growth the lifetime of the structure will decrease. Based on the damage master curve of the structure, an estimation of the remaining lifetime can be performed (see Figure 14).

CFSs can be used for strain analysis, damage monitoring and the control of manufacturing processes. Concerning strain and stress analysis an approach for CFS meshes was developed based on triangular elements with linear displacement approximation. A good correlation was found between the measurement and the finite element calculation. The use of CFS meshes can be a new approach to complement finite element analysis from the experimental

Carbon Fibre Sensor: Theory and Application 375

Concerning monitoring aspects the influence of material damages on the sensor signal were studied. It has been demonstrated that based on the integral strain measurement method the CFS is an excellent sensor to detect delaminations and matrix cracks in multidirectional reinforced laminates. Therefore, the CFS offers unique features for fracture mechanics: Measurement of strain levels and detection of matrix cracks. By means of two examples the

Strain measurement and matrix crack detection are in the focus of safe and damage tolerant composite structures making the CFS technology a complement of established sensors.

[1] Christner, C., Horoschenkoff, A. & Rapp, H. [2012]. Longitudinal and transverse strain sensitivity of embedded carbon-fibre sensors, *Journal of Composite Materials* Online

[3] Dresselhaus, M., Dresselhaus, G., Sugihara, K., Spain, I. & Goldberg, H. [1988]. *Graphite*

[4] Garrett, K. & Bailey, J. [1977]. Multiple transverse fracture in 90◦ cross-ply laminates of a

[5] Hoffmann, K. [1987]. *An introduction to measurements using strain gages*, Hottinger

[6] Horoschenkoff, A., Müller, T. & Kröll, A. [2009]. On the charaterization of the piezoresistivity of embedded carbon fibres, *17th International Conference on Composite*

[7] Horoschenkoff, A., Müller, T., Strössner, C. & Farmbauer, K. [2011]. Use of carbon-fibre sensors to determine the deflection of composite-beams, *18th International Conference on*

glass fibre-reinforced polyester, *Journal of Material Science* Vol. 12: 157–168.

*Composite Materials*, International Conference on Composite Materials, Jeju.

[2] Chung, D. [1994]. *Carbon Fiber Composites*, Butterworth-Heinemann.

CFS technologies could be demonstrated successfully:

• Determination of the deflection of a tabletop of a CT-Scanner

• Determination of the strain level and the crack density of a pressure vessel

side.

**Author details**

Christian Christner

**10. References**

Alexander Horoschenkoff

*Munich University of Applied Sciences, Germany*

*Universität der Bundeswehr München, Germany*

First: DOI: 10.1177/0021998312437983.

*Fibers and Filaments*, Springer.

Baldwin Messtechnik.

*Materials*, Edinburgh.

**Figure 21.** Strain signals of a CFS patch applied near the surface of a type II pressure vessel subjected to a pressure test

## **9. Conclusion**

There are three main aspects which made carbon fibre sensors (CFSs) very interesting to be used for composite materials:


CFSs based on a T300B 1K ex-Pan fibre exhibit an excellent linear piezoresistivity up to a strain level of 6000 *μ*m/m. The according strain sensitivity was determined as *k* = 1.71 (related to a Possion ratio of *ν* = 0.28). The longitudinal strain sensitivity *kl* of the CFS is in the range of 1.72 - 1.78. Transverse to the fibre direction CFSs exhibit a transverse strain sensitivity *kt* of approximately 0.4. This significant transverse strain sensitivity must be considered in praxis. Tension load was applied for all tests, the characterization of the compression behaviour is under examination.

A disadvantage of CFSs is the high influence of temperature on the signal which will be an aspect for future research. At the moment a long term stability of ±2 *μ*m/m (*T* = *const*.) can be achieved for a half or full bridge circuit.

CFSs can be used for strain analysis, damage monitoring and the control of manufacturing processes. Concerning strain and stress analysis an approach for CFS meshes was developed based on triangular elements with linear displacement approximation. A good correlation was found between the measurement and the finite element calculation. The use of CFS meshes can be a new approach to complement finite element analysis from the experimental side.

Concerning monitoring aspects the influence of material damages on the sensor signal were studied. It has been demonstrated that based on the integral strain measurement method the CFS is an excellent sensor to detect delaminations and matrix cracks in multidirectional reinforced laminates. Therefore, the CFS offers unique features for fracture mechanics: Measurement of strain levels and detection of matrix cracks. By means of two examples the CFS technologies could be demonstrated successfully:


Strain measurement and matrix crack detection are in the focus of safe and damage tolerant composite structures making the CFS technology a complement of established sensors.

## **Author details**

0

20

40

60

Pressure load of the vessel [bar]

80

100

120

CFS patch Pressure

18 Will-be-set-by-IN-TECH

0 50 100 150 200 250 300 350

Time [s]

**Figure 21.** Strain signals of a CFS patch applied near the surface of a type II pressure vessel subjected to

There are three main aspects which made carbon fibre sensors (CFSs) very interesting to be

CFSs based on a T300B 1K ex-Pan fibre exhibit an excellent linear piezoresistivity up to a strain level of 6000 *μ*m/m. The according strain sensitivity was determined as *k* = 1.71 (related to a Possion ratio of *ν* = 0.28). The longitudinal strain sensitivity *kl* of the CFS is in the range of 1.72 - 1.78. Transverse to the fibre direction CFSs exhibit a transverse strain sensitivity *kt* of approximately 0.4. This significant transverse strain sensitivity must be considered in praxis. Tension load was applied for all tests, the characterization of the compression behaviour is

A disadvantage of CFSs is the high influence of temperature on the signal which will be an aspect for future research. At the moment a long term stability of ±2 *μ*m/m (*T* = *const*.) can

0

a pressure test

**9. Conclusion**

used for composite materials:

• Linear piezoresistivity up to high strain levels

• Integral strain measurement method

be achieved for a half or full bridge circuit.

• Material-conformity

under examination.

100

200

300

400

Strain signal of the CFS patch [μm/m]

500

600

700

800

Alexander Horoschenkoff *Munich University of Applied Sciences, Germany*

Christian Christner *Universität der Bundeswehr München, Germany*

## **10. References**


© 2012 Mingallon and Ramaswamy, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is

distribution, and reproduction in any medium, provided the original work is properly cited.

© 2012 Mingallon and Ramaswamy, licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

**Bio-Inspired Self-Actuating Composite Materials** 

Self-organisation is a process through which the internal organisation of the system adapts to the environment to promote a specific function without being controlled from outside. Biological systems have adapted and evolved over several billion years into efficient

Form, structure, geometry, material, and behaviour are factors, which cannot be separated from one another. For example, the veins in a leaf contribute to the overall form of the leaf, its structure and geometry. At the micro scale the fibre material organisation compliments to the responsive behaviour of the leaf. Therefore, the veins display an integral coherence within the multiple functions they perform which could be termed as 'Integrated Functionality'. Integrated Functionality occurs in nature due to multiple levels of hierarchy

The premise of this research is to integrate sensing and actuation functions into a fibre composite material system. Fibre composites, which are anisotropic and heterogeneous, offer the possibility for local variations in their material properties. Embedded fibre optics would be used to sense multiple parameters and Shape memory alloys integrated into composite material for actuation. The definition of the geometry, both locally and globally would complement the adaptive functions and hence the system would display 'Integrated

**2. Less is more: Organization strategies in organic composite materials** 

Cellulose, collagen, chitin and silks are the only four types of fibrous tissues found in natural constructions (Figure 2). Biology is capable of building all living organisms using only these four materials. It does so, without further variation than changing the arrangement and organization of the fibres in the bonding substance to adapt to function specific requirements.

Maria Mingallon and Sakthivel Ramaswamy

Additional information is available at the end of the chapter

configurations, which are symbiotic with the environment.

http://dx.doi.org/10.5772/47860

in the material organization.

Functionality'.

**1. Introduction** 

properly cited.

[16] Zienkiewicz, O. & Taylor, R. [2000]. *Finite Element Method Volume 1: The Basis*, Elsevier.

## **Bio-Inspired Self-Actuating Composite Materials**

Maria Mingallon and Sakthivel Ramaswamy

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/47860

## **1. Introduction**

20 Will-be-set-by-IN-TECH

[8] Ladeveze, P. & Dantec, E. L. [1992]. Damage modelling of the elementary ply for

[9] Matzies, T., Christner, C., Müller, T., Horoschenkoff, A. & Rapp, H. [2011]. Carbon-fibre sensor meshes: Simulation and experiment, *21st International Workshop on Computational*

[10] Müller, T., Horoschenkoff, A., Rapp, H., Sause, M. & Horn, S. [2010]. Einfluss von zwischenfaserbrüchen in 0/90-laminaten auf die elektrische widerstandsänderung von

[11] Nairn, J. [1989]. The strain energy relase rate of composite microcracking: A variational

[12] Nairn, J. & Hu, S. [1994]. Matrix microcracking, *Damage Mechanics of Composite Materials*

[14] Razi, H. & Ward, S. [1996]. Principles for achieving damage tolerant primary composite aircraft structures, *11th DoD/FAA/NASA Conference on Fibrous Composites in Structural*

[15] Spain, I., K., V., Goldberg, H. & Kalnin, I. [1982]. Unusual electrical resistivity behavior

[16] Zienkiewicz, O. & Taylor, R. [2000]. *Finite Element Method Volume 1: The Basis*, Elsevier.

laminated composites, *Composite Science and Technology* Vol. 43: 257–267.

eingebetteten carbonfasern, *59th Deutscher Luft- und Raumfahrkongress*.

approach, *Journal of Composite Materials* Vol. 23: 1106–1129.

[13] Perry, C. & Lissner, H. [1955]. *The Strain Gauge Primer*, Mc Gram Hill.

of carbon fibres, *Solid State Communications* Vol. 45(No.): 817–819.

*Mechanics of Materials*, Limerick.

Vol. 9: 187–243.

*Design*.

Self-organisation is a process through which the internal organisation of the system adapts to the environment to promote a specific function without being controlled from outside. Biological systems have adapted and evolved over several billion years into efficient configurations, which are symbiotic with the environment.

Form, structure, geometry, material, and behaviour are factors, which cannot be separated from one another. For example, the veins in a leaf contribute to the overall form of the leaf, its structure and geometry. At the micro scale the fibre material organisation compliments to the responsive behaviour of the leaf. Therefore, the veins display an integral coherence within the multiple functions they perform which could be termed as 'Integrated Functionality'. Integrated Functionality occurs in nature due to multiple levels of hierarchy in the material organization.

The premise of this research is to integrate sensing and actuation functions into a fibre composite material system. Fibre composites, which are anisotropic and heterogeneous, offer the possibility for local variations in their material properties. Embedded fibre optics would be used to sense multiple parameters and Shape memory alloys integrated into composite material for actuation. The definition of the geometry, both locally and globally would complement the adaptive functions and hence the system would display 'Integrated Functionality'.

## **2. Less is more: Organization strategies in organic composite materials**

Cellulose, collagen, chitin and silks are the only four types of fibrous tissues found in natural constructions (Figure 2). Biology is capable of building all living organisms using only these four materials. It does so, without further variation than changing the arrangement and organization of the fibres in the bonding substance to adapt to function specific requirements.

Bio-Inspired Self-Actuating Composite Materials 379

Living tissues have the capability to adapt to constantly changing environmental conditions. This is achieved through iterative feedback loops, which sense, record, inform and instruct the

2.1 a - Emergence: Morphogenetic Design Strategies- Architectural Design, Academy Editions, London, Vol. 74 No 3

**Figure 2.** There are only four types of fibres in natural organisms: collagen, cellulose, chitin and silk.

In natural constructions, material is being continuously removed from places where it is not required and deposited where it can contribute to maintain the structural integrity of the structure. This concept was summarised by D'Arcy Thompson as 'growth under stresses'. Such a differentiated distribution process of fibres emerges through sensing the patterns of

Material self-organization and real-time optimization are both processes present in the formation and adaptation of biological tissues. They are termed as 'thigmo-morphogenesis' and are responsible of the resultant high performance and enormous capacity, found in natural fibre composites, to deal with unprecedented environmental conditions, unlike man-

Thigmo-morphogenesis refers to the changes in shape, structure and material properties that are produced in response to transient changes in environmental conditions. We are all familiar with the fact that many plants are capable of movement, sometimes slow as in the petals of

2.1 b - Drew, Philip- Frei Otto – Form and Structure, Granada, London, 1976, p. 22 2.1 c -http://nanotechweb.org/articles/news/1/11/5/1/0611102 (accessed on Jun 12th 2009) 2.1 d- http://upload.wikimedia.org/wikipedia/ commons/a/ab/Spider\_web\_with\_dew\_drops04.jpg

loading, or stresses constantly received by the natural organism.

made composite materials commercially available till date.

Issue May/June 2004, p. 4

(accessed on Jun 12th 2009)

fibre composite to alter its current configuration towards an optimized one.

1.a -http://cybele.bu.edu/index/leaf.jpg 1.b-http://www.buffalogardens.com/historical/ Crystal\_Palaces/body\_crystal\_palaces.html 1.c-http://www.mjausson.com/2003/img/ walk24Jun03/14gunnera\_dt.jpg 1.d - http://universe-review.ca/I10-22a-stomata.jpg (accessed on May 4th 2006)

**Figure 1.** Series of images featuring from top: hibiscus leaves, the structure at the bottom of a lily pad, the vein pattern of a leaf, and a micro-photo of stomata which aids photosynthesis.

Living tissues have the capability to adapt to constantly changing environmental conditions. This is achieved through iterative feedback loops, which sense, record, inform and instruct the fibre composite to alter its current configuration towards an optimized one.

378 Composites and Their Applications

1.a -http://cybele.bu.edu/index/leaf.jpg

(accessed on May 4th 2006)

1.d - http://universe-review.ca/I10-22a-stomata.jpg

1.b-http://www.buffalogardens.com/historical/ Crystal\_Palaces/body\_crystal\_palaces.html

the vein pattern of a leaf, and a micro-photo of stomata which aids photosynthesis.

**Figure 1.** Series of images featuring from top: hibiscus leaves, the structure at the bottom of a lily pad,

1.c-http://www.mjausson.com/2003/img/ walk24Jun03/14gunnera\_dt.jpg

2.1 a - Emergence: Morphogenetic Design Strategies- Architectural Design, Academy Editions, London, Vol. 74 No 3 Issue May/June 2004, p. 4

2.1 b - Drew, Philip- Frei Otto – Form and Structure, Granada, London, 1976, p. 22

2.1 c -http://nanotechweb.org/articles/news/1/11/5/1/0611102 (accessed on Jun 12th 2009)

2.1 d- http://upload.wikimedia.org/wikipedia/ commons/a/ab/Spider\_web\_with\_dew\_drops04.jpg (accessed on Jun 12th 2009)

**Figure 2.** There are only four types of fibres in natural organisms: collagen, cellulose, chitin and silk.

In natural constructions, material is being continuously removed from places where it is not required and deposited where it can contribute to maintain the structural integrity of the structure. This concept was summarised by D'Arcy Thompson as 'growth under stresses'. Such a differentiated distribution process of fibres emerges through sensing the patterns of loading, or stresses constantly received by the natural organism.

Material self-organization and real-time optimization are both processes present in the formation and adaptation of biological tissues. They are termed as 'thigmo-morphogenesis' and are responsible of the resultant high performance and enormous capacity, found in natural fibre composites, to deal with unprecedented environmental conditions, unlike manmade composite materials commercially available till date.

Thigmo-morphogenesis refers to the changes in shape, structure and material properties that are produced in response to transient changes in environmental conditions. We are all familiar with the fact that many plants are capable of movement, sometimes slow as in the petals of flowers which open and close, tracking of the sun by the sunflowers, the convolutions of bindweed's around supporting stems, snaking of roots around obstacles; sometimes visible to the eye, as in the dropping of leaves when mimosa pudica is touched, and exceptionally very rapid, too fast to be seen, as in the closing of the leaves of the venus flytrap.

Bio-Inspired Self-Actuating Composite Materials 381

for its application to architectural constructions. The resulting material had to have integrated sensing capabilities and actuation competences, to be able to dynamically adapt

**Figure 4.** Diagram showing the different adaptation strategies found in natural organisms. Control

Fibre optics would be used as sensors and shape memory alloys (SMA) as actuators (Figure 5). Glass fibre mats constituted the reinforcement layer for the resin-based binding matrix, in which fibre optics and shape memory alloys were embedded. Experiments were however performed substituting fibre optics for thermocouples and strain gauges, which sensed and transmitted the energy necessary for the actuation to the shape memory alloys. Energy is supplied through a source of external heat, which forms part of the experiment setup. Further research reveals that, in hot-dry climates, sun radiation could be used as the main heat source to enable actuation, with only a small percentage of the total energy being supplied by external sources at certain periods of the day when exploiting solar heat is not

In structural engineering, fibre optics is used as monitoring devices capable of measuring strain, temperature and humidity. One of their great advantages relies on their small size and fibred geometry, which converts them in perfect candidates for thin-wall structures such as fibre composite matrixes. Their receptive ability is achieved by designing the fibre optic cable to be sensitive to a specific parameter. The light pulse sent through the cable is received and further analysed by the processing unit to determine the magnitude of strain or temperature measured. Fibre optics was however substituted by strain gauges and thermocouples in the series of experiments implemented to test the performance of the self-

actuating fibre composite material presented herein.

to transient changes (Figure 4).

being the main differentiator.

possible.

In all these examples, movement and force are generated by a unique interaction of materials, structures, energy sources and sensors. Cellulose walls of parenchyma cells nonlignified, flexible in bending but stiff in tension, constitute the material; the structures are the cells themselves and their shape with the biologically active membrane that can control the passage of fluid in and out of the cells; the energy source is the chemical potential difference between the inside and the outside of the cells; the sensors are as yet unknown. These systems are essentially working as networks of interacting mini hydraulic actuators, liquid filled bags which can become turgid or flaccid and which, owing to their shape and mutual interaction translate local deformations to global ones and are also capable of generating very high stresses. Similar mechanisms can be seen in operation when leaves emerge from buds and deploy to catch sunlight. How to package the maximum surface area of material in the bud and to expand it rapidly and efficiently is the result of smart folding strategies, turgor pressure and growth. [1]

http://www.tucsongardener.com/Year02/Fall2002/ photos/sensitivefold.JPG

**Figure 3.** Undisturbed delicate leaves of the sensitive plant mimosa pudica, which closes its leaves when lightly touched.

## **3. Alive: Hypothesis behind a smart composite material**

The research presented herein proposes a bio-inspired synthetic self-actuating fibre composite, which emulates the morpho-mechanical processes found in natural fibre tissues, for its application to architectural constructions. The resulting material had to have integrated sensing capabilities and actuation competences, to be able to dynamically adapt to transient changes (Figure 4).

380 Composites and Their Applications

strategies, turgor pressure and growth. [1]

http://www.tucsongardener.com/Year02/Fall2002/ photos/sensitivefold.JPG

**3. Alive: Hypothesis behind a smart composite material** 

when lightly touched.

**Figure 3.** Undisturbed delicate leaves of the sensitive plant mimosa pudica, which closes its leaves

The research presented herein proposes a bio-inspired synthetic self-actuating fibre composite, which emulates the morpho-mechanical processes found in natural fibre tissues,

flowers which open and close, tracking of the sun by the sunflowers, the convolutions of bindweed's around supporting stems, snaking of roots around obstacles; sometimes visible to the eye, as in the dropping of leaves when mimosa pudica is touched, and exceptionally very

In all these examples, movement and force are generated by a unique interaction of materials, structures, energy sources and sensors. Cellulose walls of parenchyma cells nonlignified, flexible in bending but stiff in tension, constitute the material; the structures are the cells themselves and their shape with the biologically active membrane that can control the passage of fluid in and out of the cells; the energy source is the chemical potential difference between the inside and the outside of the cells; the sensors are as yet unknown. These systems are essentially working as networks of interacting mini hydraulic actuators, liquid filled bags which can become turgid or flaccid and which, owing to their shape and mutual interaction translate local deformations to global ones and are also capable of generating very high stresses. Similar mechanisms can be seen in operation when leaves emerge from buds and deploy to catch sunlight. How to package the maximum surface area of material in the bud and to expand it rapidly and efficiently is the result of smart folding

rapid, too fast to be seen, as in the closing of the leaves of the venus flytrap.

**Figure 4.** Diagram showing the different adaptation strategies found in natural organisms. Control being the main differentiator.

Fibre optics would be used as sensors and shape memory alloys (SMA) as actuators (Figure 5). Glass fibre mats constituted the reinforcement layer for the resin-based binding matrix, in which fibre optics and shape memory alloys were embedded. Experiments were however performed substituting fibre optics for thermocouples and strain gauges, which sensed and transmitted the energy necessary for the actuation to the shape memory alloys. Energy is supplied through a source of external heat, which forms part of the experiment setup. Further research reveals that, in hot-dry climates, sun radiation could be used as the main heat source to enable actuation, with only a small percentage of the total energy being supplied by external sources at certain periods of the day when exploiting solar heat is not possible.

In structural engineering, fibre optics is used as monitoring devices capable of measuring strain, temperature and humidity. One of their great advantages relies on their small size and fibred geometry, which converts them in perfect candidates for thin-wall structures such as fibre composite matrixes. Their receptive ability is achieved by designing the fibre optic cable to be sensitive to a specific parameter. The light pulse sent through the cable is received and further analysed by the processing unit to determine the magnitude of strain or temperature measured. Fibre optics was however substituted by strain gauges and thermocouples in the series of experiments implemented to test the performance of the selfactuating fibre composite material presented herein.

Bio-Inspired Self-Actuating Composite Materials 383

**Figure 6.** Picture illustrates the calibration process of the strain gauges processing unit.

**Figure 7.** Picture features the strain gauge during its calibration and testing on a polyester strip.

**Figure 5.** Nitinol based shape memory alloy. Shaped as a ribbon featuring an actuation temperature of 65°C.

Strain gauges are resistance-based sensors employed to measure variations in length of a parent component, factored by the component's original length. Strain gauges consist of a thin wire of metal foil, wrapped across a grid, which is also attached to a thin flexible backing material impregnated with glue, for adhesion to the parent component for which strain is to be monitored. This setup allows the wrapped wire to stretch or compress thus, detecting elongations and contractions felt by the parent component (Figures 6 and 7).

## **4. Experimental: Understanding the behaviour of SMAs**

Nitinol (NiTi) is a specifically manufactured alloy of nickel and titanium, which has the ability to generate significant force upon changing shape. NiTi shape memory alloys can exist in three different crystal structures or phases called martensite, stress-induced martensite and austenite. At low temperature, the alloy exists as martensite, which is weak, soft and highly deformable. Stress-induced martensite (or super elastic NiTi) is highly elastic and is present at a temperature slightly higher than its transformation temperature. The austenite is the strongest, higher temperature phase, present in NiTi. Most of the physical properties of austenite and martensite vary during phase transformations; among these properties are the Young's modulus, the heat capacity, the latent heat and the thermal conductivity.

**Figure 6.** Picture illustrates the calibration process of the strain gauges processing unit.

65°C.

**Figure 5.** Nitinol based shape memory alloy. Shaped as a ribbon featuring an actuation temperature of

Strain gauges are resistance-based sensors employed to measure variations in length of a parent component, factored by the component's original length. Strain gauges consist of a thin wire of metal foil, wrapped across a grid, which is also attached to a thin flexible backing material impregnated with glue, for adhesion to the parent component for which strain is to be monitored. This setup allows the wrapped wire to stretch or compress thus, detecting elongations and contractions felt by the parent component (Figures 6 and 7).

Nitinol (NiTi) is a specifically manufactured alloy of nickel and titanium, which has the ability to generate significant force upon changing shape. NiTi shape memory alloys can exist in three different crystal structures or phases called martensite, stress-induced martensite and austenite. At low temperature, the alloy exists as martensite, which is weak, soft and highly deformable. Stress-induced martensite (or super elastic NiTi) is highly elastic and is present at a temperature slightly higher than its transformation temperature. The austenite is the strongest, higher temperature phase, present in NiTi. Most of the physical properties of austenite and martensite vary during phase transformations; among these properties are the

**4. Experimental: Understanding the behaviour of SMAs** 

Young's modulus, the heat capacity, the latent heat and the thermal conductivity.

**Figure 7.** Picture features the strain gauge during its calibration and testing on a polyester strip.

Shape setting is essential to train the NiTi alloys to remember a specific shape. An actuator element designed for a particular purpose generally requires the setting of a custom shape. Shape setting is similar in all forms of nitinol, such as, wires, ribbons, strips, sheets, tubes or bars. It is accomplished by constraining the nitinol element on a mandrel or a fixture of the desired shape while applying an appropriate heat treatment. The heat treatment parameters and the properties of the actuator element are critical for the consequent behaviour of the NiTi, and usually need to be determined experimentally. In principle, temperatures as low as 400°C and heating times as short as 1 to 2 minutes are sufficient to set the shape, but generally one uses a temperature closer to 500°C and a heating time period of at least 5 minutes. Rapid cooling of the alloy is preferred via a water quench or rapid air-cooling. Higher heat treatment times and temperatures will increase the actuation temperature of the alloy and often results on sharper thermal responses. There is also an accompanying decrease in the ability of the actuator to resist permanent deformation. [2]

Bio-Inspired Self-Actuating Composite Materials 385

**Figure 9.** Shape memory alloy and mandrel following its removal from the kiln, after the cooling

process.

The first set of experiments focused on understanding the process of shape setting in SMAs outlined above, and their actuation behaviour against temperature. These were especially motivated by the need to quantify their lifting capacity against time for their latter integration in the fibre composite matrix. The SMAs used for these experiments were ribbons with an actuation temperature of 65°C, 1.2mm thick, 4.6mm wide and 270mm long.

The shape setting process required the SMAs to be heated at 500°C for at least 5 minutes. The SMA ribbons were trained by fixing them around metal pipes, which helped maintaining the SMAs in place during the heating process. They were subsequently removed from the oven and immediately immersed in cold water whilst maintaining the imposed bent shape throughout the cooling procedure (Figures 8 and 9).

**Figure 8.** Shape memory alloys and mandrels inside kiln after heating process had finalised.

Shape setting is essential to train the NiTi alloys to remember a specific shape. An actuator element designed for a particular purpose generally requires the setting of a custom shape. Shape setting is similar in all forms of nitinol, such as, wires, ribbons, strips, sheets, tubes or bars. It is accomplished by constraining the nitinol element on a mandrel or a fixture of the desired shape while applying an appropriate heat treatment. The heat treatment parameters and the properties of the actuator element are critical for the consequent behaviour of the NiTi, and usually need to be determined experimentally. In principle, temperatures as low as 400°C and heating times as short as 1 to 2 minutes are sufficient to set the shape, but generally one uses a temperature closer to 500°C and a heating time period of at least 5 minutes. Rapid cooling of the alloy is preferred via a water quench or rapid air-cooling. Higher heat treatment times and temperatures will increase the actuation temperature of the alloy and often results on sharper thermal responses. There is also an accompanying

The first set of experiments focused on understanding the process of shape setting in SMAs outlined above, and their actuation behaviour against temperature. These were especially motivated by the need to quantify their lifting capacity against time for their latter integration in the fibre composite matrix. The SMAs used for these experiments were ribbons with an actuation temperature of 65°C, 1.2mm thick, 4.6mm wide and 270mm long. The shape setting process required the SMAs to be heated at 500°C for at least 5 minutes. The SMA ribbons were trained by fixing them around metal pipes, which helped maintaining the SMAs in place during the heating process. They were subsequently removed from the oven and immediately immersed in cold water whilst maintaining the

decrease in the ability of the actuator to resist permanent deformation. [2]

imposed bent shape throughout the cooling procedure (Figures 8 and 9).

**Figure 8.** Shape memory alloys and mandrels inside kiln after heating process had finalised.

**Figure 9.** Shape memory alloy and mandrel following its removal from the kiln, after the cooling process.

Bio-Inspired Self-Actuating Composite Materials 387

Subsequent experiments focused on demonstrating quite simplistically the actuation abilities of our SMAs. We first wrapped the SMAs ribbons with a piece of felt to better illustrate the resulting shape change. The outcome, featured in Figure 10, was exactly what we expected, with the SMA achieving the 'memorized' shape quite rapidly. The experiment that followed tested the behaviour of the actuator under the tension exerted by a thin fabric membrane. The fabric was anchored to a circular frame installed on a planar surface with a heat-gun pointing straight downwards onto the alloy. The ribbon curved consistently, pulling the thin membrane up steadily, as soon as the actuation temperature was reached. Figure 11 illustrates the results. While these were both very simplistic experiments, they guided our research towards

quantifying the actuation force of our SMAs when embedded in a fibre composite.

**Figure 11.** Sequential photograms featuring the actuation of the shape memory alloy sewed to a thin

**Figure 12.** Sequential photograms featuring the load lifting tests undertaken.

fabric membrane.

**Figure 10.** Sequential photograms featuring the actuation of the shape memory alloy ribbon sewed onto a piece of felt.

Subsequent experiments focused on demonstrating quite simplistically the actuation abilities of our SMAs. We first wrapped the SMAs ribbons with a piece of felt to better illustrate the resulting shape change. The outcome, featured in Figure 10, was exactly what we expected, with the SMA achieving the 'memorized' shape quite rapidly. The experiment that followed tested the behaviour of the actuator under the tension exerted by a thin fabric membrane. The fabric was anchored to a circular frame installed on a planar surface with a heat-gun pointing straight downwards onto the alloy. The ribbon curved consistently, pulling the thin membrane up steadily, as soon as the actuation temperature was reached. Figure 11 illustrates the results. While these were both very simplistic experiments, they guided our research towards quantifying the actuation force of our SMAs when embedded in a fibre composite.

386 Composites and Their Applications

a piece of felt.

**Figure 10.** Sequential photograms featuring the actuation of the shape memory alloy ribbon sewed onto

**Figure 11.** Sequential photograms featuring the actuation of the shape memory alloy sewed to a thin fabric membrane.

**Figure 12.** Sequential photograms featuring the load lifting tests undertaken.

The ribbon was this time set up as a simply supported beam under sequential loading increments, the aim being to quantify the SMAs actuation force against time (Figure 12). Whenever the load was increased, the actuation time was measured. Each load increment was quantified as 0.56 N, i.e. the weight of the nuts used. Figure 13 shows the load-time relationship when actuation occurred, lifting up the ribbon and the imposed weights. Experiments proved that the ribbon under testing could lift a load of 8.83N, which equates to 100 times its selfweight. The time taken to lift the first nut was 8 seconds, while lifting the group of nuts weighting 8.83N was 18 seconds. Assuming the 8 seconds for the first lift is the time it takes the ribbon to achieve the actuation temperature, the actual actuation time to lift 8.83N was 10 seconds. This series of experiments provided us with substantial information on the behaviour of the SMAs and particularly, how much force they could exert and how rapidly.

Bio-Inspired Self-Actuating Composite Materials 389

**Figure 14.** Series of photograms featuring the calibration of the shape memory alloy ribbon. Actuation temperature and curvature changes were measured and subsequently registered to inform the building

Further experiments followed the preliminary tests described above, contributing to the refinement of the final model. These were aimed to test the elasticity of different polymers, from highly deformable to more rigid mixtures. Finding a polymer with an appropriate elasticity modulus was key to achieve the intended degree of actuation in the fibre composite material. Figure 15 features a failed setup using a silicon-based composite, which resulted extremely flexible and heavy to be anyhow actuated by four SMA ribbons. The test did serve however to guide the research towards the use of polymers with higher Young's

Our final experimental model consisted of a sandwich structure made of two layers of a glass fibre mat bonded by an epoxy-based resin. A total of four SMA alloys were embedded in between the two layers of glass fibres. Figure 16 features a diagram illustrating the set up

of the final prototype.

modulus.

of the model.

**5. Composite: Building the material system** 

**Figure 13.** Graph featuring the load lifting capacity of the ribbon, against the time taken to actuate.

The next step was to calibrate the curvature change of the SMAs in relation to temperature. We had purchased ribbons with a theoretical actuation temperature of 65°C. However, we knew that the behaviour of the alloy and ultimately its actuation temperature could have been altered during the shape training process. A simple experiment using a thermocouple and a unit controlling the temperature of the alloy served to measure the curvature of the alloy at different temperature increments (Figure 14). The experiment demonstrated that the shape change did not occur instantaneously; instead, it was a steady process that started at 38°C, with the alloy reaching its maximum curvature at 58°C, as supposed to its theoretical actuation temperature of 65°C. It was clear that the training regime of the alloy had an impact on its later behaviour. The high curvature of the trained shape could have also altered the resulting actuation performance. This test also provided us with key data regarding the maximum curvature change that the alloy could achieve when setup freely. The outcome of this calibration exercise served to feed the construction of the final prototype.

#### Bio-Inspired Self-Actuating Composite Materials 389

**Figure 14.** Series of photograms featuring the calibration of the shape memory alloy ribbon. Actuation temperature and curvature changes were measured and subsequently registered to inform the building of the final prototype.

## **5. Composite: Building the material system**

388 Composites and Their Applications

The ribbon was this time set up as a simply supported beam under sequential loading increments, the aim being to quantify the SMAs actuation force against time (Figure 12). Whenever the load was increased, the actuation time was measured. Each load increment was quantified as 0.56 N, i.e. the weight of the nuts used. Figure 13 shows the load-time relationship when actuation occurred, lifting up the ribbon and the imposed weights. Experiments proved that the ribbon under testing could lift a load of 8.83N, which equates to 100 times its selfweight. The time taken to lift the first nut was 8 seconds, while lifting the group of nuts weighting 8.83N was 18 seconds. Assuming the 8 seconds for the first lift is the time it takes the ribbon to achieve the actuation temperature, the actual actuation time to lift 8.83N was 10 seconds. This series of experiments provided us with substantial information on the behaviour

of the SMAs and particularly, how much force they could exert and how rapidly.

**Figure 13.** Graph featuring the load lifting capacity of the ribbon, against the time taken to actuate.

this calibration exercise served to feed the construction of the final prototype.

The next step was to calibrate the curvature change of the SMAs in relation to temperature. We had purchased ribbons with a theoretical actuation temperature of 65°C. However, we knew that the behaviour of the alloy and ultimately its actuation temperature could have been altered during the shape training process. A simple experiment using a thermocouple and a unit controlling the temperature of the alloy served to measure the curvature of the alloy at different temperature increments (Figure 14). The experiment demonstrated that the shape change did not occur instantaneously; instead, it was a steady process that started at 38°C, with the alloy reaching its maximum curvature at 58°C, as supposed to its theoretical actuation temperature of 65°C. It was clear that the training regime of the alloy had an impact on its later behaviour. The high curvature of the trained shape could have also altered the resulting actuation performance. This test also provided us with key data regarding the maximum curvature change that the alloy could achieve when setup freely. The outcome of Further experiments followed the preliminary tests described above, contributing to the refinement of the final model. These were aimed to test the elasticity of different polymers, from highly deformable to more rigid mixtures. Finding a polymer with an appropriate elasticity modulus was key to achieve the intended degree of actuation in the fibre composite material. Figure 15 features a failed setup using a silicon-based composite, which resulted extremely flexible and heavy to be anyhow actuated by four SMA ribbons. The test did serve however to guide the research towards the use of polymers with higher Young's modulus.

Our final experimental model consisted of a sandwich structure made of two layers of a glass fibre mat bonded by an epoxy-based resin. A total of four SMA alloys were embedded in between the two layers of glass fibres. Figure 16 features a diagram illustrating the set up of the model.

Bio-Inspired Self-Actuating Composite Materials 391

**Figure 17.** Silicone heating patches used in the experiments. Advantages of the use of these patches are

their lightweight, thin and flexible structure, while being able to heat up to 232°C.

**Figure 18.** Pictures illustrating the construction of the final prototype.

**Figure 15.** Sequential photograms featuring the failed experiment using a silicon-based composite.

**Figure 16.** Diagram featuring the arrangement followed for the assembly of the final prototype.

**Figure 15.** Sequential photograms featuring the failed experiment using a silicon-based composite.

**Figure 16.** Diagram featuring the arrangement followed for the assembly of the final prototype.

**Figure 17.** Silicone heating patches used in the experiments. Advantages of the use of these patches are their lightweight, thin and flexible structure, while being able to heat up to 232°C.

**Figure 18.** Pictures illustrating the construction of the final prototype.

The sensing capabilities of the model were based on an active-dummy method (also known as Wheatstone's bridge) that allowed measurement of real-time changes in strain on the parent shell structure. Two gauges were then connected to a processing unit, which translated the strain signal into a voltage output of 2 volts, when elongation was detected, and 0 volts, once it ceased. This voltage was then sent to the controller unit, which turned on and off a set of silicon heating strips upon which a shape memory alloy wire was glued (Figure 17). A set of thermocouples were used to measure the temperature of the shape memory alloys as the silicon heating strips commenced to heat them. The processing unit to which the thermocouples were connected would automatically stop the heating process once the actuation temperature of the actuators was reached (Figures 18, 19 and 20).

Bio-Inspired Self-Actuating Composite Materials 393

**Figure 20.** Series of pictures showing preliminary tests of the actuation in the laboratory.

for the strain gauges, the processing and control units, as well as, the heating strips.

by superimposing the actuation stages described above.

**6. Architecture with smart composites** 

Alternative methods to the use of silicon heating strips could have been piezoelectric fibres, which can generate electric potential in response to applied mechanical stress. The implementation of piezoelectric fibres in our setup could have potentially avoided the need

Figure 21 features the set up of the final prototype, including the strain gauges processing unit and the different controlling devices. Figure 22 shows the actuation response of the prototype at the temperatures of 30°C, 42°C and 58°C. At 30°C the shape of the prototype has not yet been altered; it is therefore the initial shape which serves as reference of the nonactuated model. At 42°C, the strain gauges detected actuation had commenced. From previous tests, we knew that if setup freely, the alloys would start actuation at 38°C. However, the alloys were now embedded in a fibre composite, which contributed to an increase in stiffness. It was more difficult for the alloy now to start curving and as a result, to spread that deformation to the material it was embedded in. This caused a delay on the actuation of 4°C when compared to the previously tested model where the SMA did not experience external material constraints. At 58°C the prototype was about to reach its highest curvature. The shape change can be easily compared thanks to the photogram made

On an architectural scale, the aim was to introduce actuation not through and external heat

source but by utilizing the diurnal temperature variation in the environment.

**Figure 19.** Pictures illustrating the soldering and preparation of the strain gauges on the final prototype.

#### Bio-Inspired Self-Actuating Composite Materials 393

**Figure 20.** Series of pictures showing preliminary tests of the actuation in the laboratory.

Alternative methods to the use of silicon heating strips could have been piezoelectric fibres, which can generate electric potential in response to applied mechanical stress. The implementation of piezoelectric fibres in our setup could have potentially avoided the need for the strain gauges, the processing and control units, as well as, the heating strips.

Figure 21 features the set up of the final prototype, including the strain gauges processing unit and the different controlling devices. Figure 22 shows the actuation response of the prototype at the temperatures of 30°C, 42°C and 58°C. At 30°C the shape of the prototype has not yet been altered; it is therefore the initial shape which serves as reference of the nonactuated model. At 42°C, the strain gauges detected actuation had commenced. From previous tests, we knew that if setup freely, the alloys would start actuation at 38°C. However, the alloys were now embedded in a fibre composite, which contributed to an increase in stiffness. It was more difficult for the alloy now to start curving and as a result, to spread that deformation to the material it was embedded in. This caused a delay on the actuation of 4°C when compared to the previously tested model where the SMA did not experience external material constraints. At 58°C the prototype was about to reach its highest curvature. The shape change can be easily compared thanks to the photogram made by superimposing the actuation stages described above.

## **6. Architecture with smart composites**

392 Composites and Their Applications

19 and 20).

prototype.

The sensing capabilities of the model were based on an active-dummy method (also known as Wheatstone's bridge) that allowed measurement of real-time changes in strain on the parent shell structure. Two gauges were then connected to a processing unit, which translated the strain signal into a voltage output of 2 volts, when elongation was detected, and 0 volts, once it ceased. This voltage was then sent to the controller unit, which turned on and off a set of silicon heating strips upon which a shape memory alloy wire was glued (Figure 17). A set of thermocouples were used to measure the temperature of the shape memory alloys as the silicon heating strips commenced to heat them. The processing unit to which the thermocouples were connected would automatically stop the heating process once the actuation temperature of the actuators was reached (Figures 18,

**Figure 19.** Pictures illustrating the soldering and preparation of the strain gauges on the final

On an architectural scale, the aim was to introduce actuation not through and external heat source but by utilizing the diurnal temperature variation in the environment.

Bio-Inspired Self-Actuating Composite Materials 395

**Figure 23.** A view of the shell with the actuating fenestrations

**Figure 24.** An interior view from the shell

Hot and dry climatic zones which have a considerable diurnal variation in temperature would be the most appropriate to exploit the environmental energy for the efficient functioning of the adaptive system. While actuation temperatures of commercially available

**Figure 21.** Final setup of the prototype including the strain gauges processing unit, the single input controller, the actuation temperature controller and the final prototype.

**Figure 22.** Superimposed photograms featuring three resulting shapes of the actuation at the indicated temperatures.

**Figure 23.** A view of the shell with the actuating fenestrations

temperatures.

**Figure 21.** Final setup of the prototype including the strain gauges processing unit, the single input

**Figure 22.** Superimposed photograms featuring three resulting shapes of the actuation at the indicated

controller, the actuation temperature controller and the final prototype.

**Figure 24.** An interior view from the shell

Hot and dry climatic zones which have a considerable diurnal variation in temperature would be the most appropriate to exploit the environmental energy for the efficient functioning of the adaptive system. While actuation temperatures of commercially available shape memory alloys range between 30°C and 95°C, the specific alloys used for the experimental setup had actuation temperatures ranging from 35°C to 65°C. In hot and dry climatic zones the variation in atmospheric temperature is measured to range from 22°C to 44°C in the summer months. Surface temperature of the alloys would therefore easily reach the required 35°C which would initiate their actuation.

**Chapter 16** 

© 2012 de Oliveira and de Oliveira, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is

distribution, and reproduction in any medium, provided the original work is properly cited.

© 2012 de Oliveira and de Oliveira, licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use,

properly cited.

**Composite Material and Optical Fibres** 

For ease of handling and polishing, optical fibres are generally mounted in some form of rigid structure. A schematic of a typical fibre termination used in astronomical instruments (typical of multiple-fibre spectrographs) is show in Fig. 1. The fibre is first placed within a flexible tube (polyimide or similar), often referred to as the strain relief tube. The fibre and tube are placed within a rigid ferrule. Adhesive is applied to the fibre and tubing to fix them in place. The ferrule can then be easily manipulated for polishing, or mounting within an instrument, without risk of damage to the fibre. The role of the strain relief tube is to prevent stresses occurring at the point where the fibre enters the ferrule given bending at this point may lead to breakages. For coupling an array of optical fibres to a microlens array, such as in IFU (Integral Field Unity), a brass plate with an array of drilled microholes may be used. Optical fibres

positioned in an array of accurately drilled holes, as illustrated schematically in Fig. 2.

**Figure 1.** Schematic diagram of a single fibre mounting assembly: 1, core; 2, cladding; 3, polyamide

buffer; 4, acrylate buffer; 5, epoxy; 6, plastic tube; 7, epoxy; 8, ferrule steel tube.

Antonio C. de Oliveira and Ligia S. de Oliveira

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/76664

**1. Introduction** 

Self-actuation potential of any structure invariably necessitates integrating decision-making abilities and thus intelligent behaviour into the adaptive system. The morphological definition of the structure plays a key role in adaptation and has to be coherent with the actuation logic. The material tests and experiments conducted, establish the premise for the architectural application of the self-actuating fibre composite system developed herein. The study branches further into the utilization of such a self-adaptive material system in an architectural application, with reference to context specific climatic data (Figures 23 and 24).

The image shows a large span fibre composite shell structure with actuating fenestrations. The shape memory alloys embedded in the fenestrations allow the structure to open and close based on the external environmental conditions. The opening are strategically positioned in a manner in which they do not affect the structural stability at the same time enhance the interior lighting and wind flow pattern.

## **Author details**

Maria Mingallon *ARUP, McGill University, School of Architecture, Canada* 

Sakthivel Ramaswamy *KRR Group, India* 

## **Acknowledgement**

We would like to thank our tutors; Mike Weinstock for his involvement and invaluable guidance, and Michael Hensel for his help and encouragement. George Jeronimidis for his immense help in developing our research and in performing the physical experiments. His research on biomimetics is the foundation for this project. We would also like to thank Stylianos Dritsas, for his essential input in evolving the geometry. Professors Kevin Kuang and W.J. Cantwell for sharing their knowledge and research on shape memory alloys and fibre optics. We would finally like to thank our families and friends for their constant support and invaluable encouragement.

## **7. References**


## **Composite Material and Optical Fibres**

Antonio C. de Oliveira and Ligia S. de Oliveira

Additional information is available at the end of the chapter

http://dx.doi.org/10.5772/76664

## **1. Introduction**

396 Composites and Their Applications

**Author details** 

Maria Mingallon

Sakthivel Ramaswamy *KRR Group, India* 

**Acknowledgement** 

**7. References** 

*ARUP,* 

the required 35°C which would initiate their actuation.

enhance the interior lighting and wind flow pattern.

*McGill University, School of Architecture, Canada* 

support and invaluable encouragement.

shape memory alloys range between 30°C and 95°C, the specific alloys used for the experimental setup had actuation temperatures ranging from 35°C to 65°C. In hot and dry climatic zones the variation in atmospheric temperature is measured to range from 22°C to 44°C in the summer months. Surface temperature of the alloys would therefore easily reach

Self-actuation potential of any structure invariably necessitates integrating decision-making abilities and thus intelligent behaviour into the adaptive system. The morphological definition of the structure plays a key role in adaptation and has to be coherent with the actuation logic. The material tests and experiments conducted, establish the premise for the architectural application of the self-actuating fibre composite system developed herein. The study branches further into the utilization of such a self-adaptive material system in an architectural application, with reference to context specific climatic data (Figures 23 and 24). The image shows a large span fibre composite shell structure with actuating fenestrations. The shape memory alloys embedded in the fenestrations allow the structure to open and close based on the external environmental conditions. The opening are strategically positioned in a manner in which they do not affect the structural stability at the same time

We would like to thank our tutors; Mike Weinstock for his involvement and invaluable guidance, and Michael Hensel for his help and encouragement. George Jeronimidis for his immense help in developing our research and in performing the physical experiments. His research on biomimetics is the foundation for this project. We would also like to thank Stylianos Dritsas, for his essential input in evolving the geometry. Professors Kevin Kuang and W.J. Cantwell for sharing their knowledge and research on shape memory alloys and fibre optics. We would finally like to thank our families and friends for their constant

[1] Jeronimidis, George, 'Biomimetics - Differentiation / Integration / Emergence, Sensing – Actuation –Control', - Lecture at the Architectural Association, London, 2009. [2] Smith,S. A, 'Shape Setting Nitinol', - Proceedings of the Materials and Processes for Medical Devices Conference, pp 266 – 270. edited by S. Shrivastava, ASM International, Sept., 2003.

For ease of handling and polishing, optical fibres are generally mounted in some form of rigid structure. A schematic of a typical fibre termination used in astronomical instruments (typical of multiple-fibre spectrographs) is show in Fig. 1. The fibre is first placed within a flexible tube (polyimide or similar), often referred to as the strain relief tube. The fibre and tube are placed within a rigid ferrule. Adhesive is applied to the fibre and tubing to fix them in place. The ferrule can then be easily manipulated for polishing, or mounting within an instrument, without risk of damage to the fibre. The role of the strain relief tube is to prevent stresses occurring at the point where the fibre enters the ferrule given bending at this point may lead to breakages. For coupling an array of optical fibres to a microlens array, such as in IFU (Integral Field Unity), a brass plate with an array of drilled microholes may be used. Optical fibres positioned in an array of accurately drilled holes, as illustrated schematically in Fig. 2.

**Figure 1.** Schematic diagram of a single fibre mounting assembly: 1, core; 2, cladding; 3, polyamide buffer; 4, acrylate buffer; 5, epoxy; 6, plastic tube; 7, epoxy; 8, ferrule steel tube.

© 2012 de Oliveira and de Oliveira, licensee InTech. This is an open access chapter distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. © 2012 de Oliveira and de Oliveira, licensee InTech. This is a paper distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/3.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

This system, called microholes array, contains a grid of holes spaced by the pitch of the microlens array. The holes are machined using custom made drills with two different diameters. This produces a stepped hole, with the smaller diameter hole used for fibre positioning while the larger hole is used to accommodate a ferrule. The small holes are approximately 10 m larger than the fibre diameter to allow sufficient space for a glue to penetrate. Using a stepped hole also allows a greater depth of material to be machined than by using a small drill alone. This permits a thicker, hence more robust, piece of material to be used. A support plate is also used, positioned above the fibre-positioning array with spacers, to maintain accurate angular alignment of the ferrules with respect to the microlens optical axis. Each ferrule contains a polyimide strain relief tube to prevent mechanical stress, occurring at the point where the fibre enters the ferrule. To secure the fibres, ferrules, and polyamide tubes in place the whole input assembly is immersed in a container of EPOTEK 301-2 adhesive. This epoxy is a natural choice due to its excellent wicking properties and low shrinkage upon curing. After curing, which takes approximately three days at room temperature; any excess glue is removed prior to optical polishing.

Composite Material and Optical Fibres 399

ideal condition requires a material with elasticity controlled so as not to cause stress or shift the positioning of optical fibre under temperature gradients. For just such purposes, we have developed a special composite formed from a mixture of EPO-TEK 301-2 and some refractory material oxide in nano-particle form, cured and submitted to a customized thermal treatment. To avoid bubbles and points of stress, this mixture is prepared in a separate receptacle inside a vacuum chamber. The resulting material is more resistant and harder than EPO-TEK 301-2 and is found to be well suited to the fabrication of optical fibre arrays. An important secondary characteristic is the ease with which it can be polished. This feature is a result of the micro particles, which keep the polished surface very homogeneous during the final polishing procedure. The resulting composite combines the beneficial characteristics of both the epoxy and the oxide; main factor its coefficient of thermal expansion is significantly lower than simple solidified epoxy; the exact value depending on the relative concentrations. While the characteristics of this particular composite are still under study, it is clearly possible deploy this material in the construction of devices for

Similar microholes arrays and the support plates of the Fig. 2, used to construct Eucalyptus IFU, were made with toolmakers brass (de Oliveira et al., 2002). The problem here is that differential expansion between the metal array and the glass microlens substrate may lead to the bond between them failing at low temperatures. Although the coefficient of thermal expansion of epoxy is much greater than those of steel, brass or glass, the elasticity of the epoxy accommodates the dimensional changes without breakage: however, this can

It is well known that mechanical deformation causes focal ratio degradation (FRD) by the formation of microbends in the fibre (Clayton 1989). FRD is a non-conservation of *étendue* such that the focal ratio is broadened by propagation in the fibre. When mounting the fibre, the appropriate epoxy and tubing should be selected, and general care must be taken to minimize mechanical stress and avoid additional FRD (de Oliveira et al., 2005). This is straightforward at room temperature, but greater care must be taken in the choice of materials for use at low temperatures. When the fibre assembly is cooled to temperatures around -10 °C, the epoxy, tubing and ferrule will all shrink differentially, and this may cause the level of FRD to increase. There is other problem when the fibre assembly is warmed to around 20 °C and cooled to around -10 °C. The UV epoxy, currently used used to cement the metal and the glass may be damaged if the system will be submitted several times at big changes of temperature. In this case the system may detach in places due the thermal

Microholes array and support plate made with solidified EPOTEK represent a first step to change the metallic base for a polymeric base. The choice of the EPOTEK 301-2 is appropriate due to its excellent wicking properties and low shrinkage upon curing. This properties are very good to use in optical fibres system, so that, if it is possible to get plates

several fibre instruments.

gradient.

**2. New materials to support optical fibres** 

introduce a small amount of stress build-up.

**Figure 2.** Schematic micro lens array and fibre positioning array used to constructed IFUs

The problem here may be an increase of FRD (Focal Ratio Degradation) caused by contraction of the metal ferrule or brass plate at low temperature causing stress on the fibres and consequent loss of throughput. Astronomic instruments like that in general work in environments with significant thermal gradients, a common characteristic of ground-based observatories. An interesting alternative to the conventional steel ferrule may be a quartz tube. Quartz material has no problems of contraction in the temperature gradients experienced in that places, -10 °C to 20 °C, but is very expensive and difficult to obtain. The ideal condition requires a material with elasticity controlled so as not to cause stress or shift the positioning of optical fibre under temperature gradients. For just such purposes, we have developed a special composite formed from a mixture of EPO-TEK 301-2 and some refractory material oxide in nano-particle form, cured and submitted to a customized thermal treatment. To avoid bubbles and points of stress, this mixture is prepared in a separate receptacle inside a vacuum chamber. The resulting material is more resistant and harder than EPO-TEK 301-2 and is found to be well suited to the fabrication of optical fibre arrays. An important secondary characteristic is the ease with which it can be polished. This feature is a result of the micro particles, which keep the polished surface very homogeneous during the final polishing procedure. The resulting composite combines the beneficial characteristics of both the epoxy and the oxide; main factor its coefficient of thermal expansion is significantly lower than simple solidified epoxy; the exact value depending on the relative concentrations. While the characteristics of this particular composite are still under study, it is clearly possible deploy this material in the construction of devices for several fibre instruments.

## **2. New materials to support optical fibres**

398 Composites and Their Applications

This system, called microholes array, contains a grid of holes spaced by the pitch of the microlens array. The holes are machined using custom made drills with two different diameters. This produces a stepped hole, with the smaller diameter hole used for fibre positioning while the larger hole is used to accommodate a ferrule. The small holes are approximately 10 m larger than the fibre diameter to allow sufficient space for a glue to penetrate. Using a stepped hole also allows a greater depth of material to be machined than by using a small drill alone. This permits a thicker, hence more robust, piece of material to be used. A support plate is also used, positioned above the fibre-positioning array with spacers, to maintain accurate angular alignment of the ferrules with respect to the microlens optical axis. Each ferrule contains a polyimide strain relief tube to prevent mechanical stress, occurring at the point where the fibre enters the ferrule. To secure the fibres, ferrules, and polyamide tubes in place the whole input assembly is immersed in a container of EPOTEK 301-2 adhesive. This epoxy is a natural choice due to its excellent wicking properties and low shrinkage upon curing. After curing, which takes approximately three days at room

temperature; any excess glue is removed prior to optical polishing.

**Figure 2.** Schematic micro lens array and fibre positioning array used to constructed IFUs

The problem here may be an increase of FRD (Focal Ratio Degradation) caused by contraction of the metal ferrule or brass plate at low temperature causing stress on the fibres and consequent loss of throughput. Astronomic instruments like that in general work in environments with significant thermal gradients, a common characteristic of ground-based observatories. An interesting alternative to the conventional steel ferrule may be a quartz tube. Quartz material has no problems of contraction in the temperature gradients experienced in that places, -10 °C to 20 °C, but is very expensive and difficult to obtain. The Similar microholes arrays and the support plates of the Fig. 2, used to construct Eucalyptus IFU, were made with toolmakers brass (de Oliveira et al., 2002). The problem here is that differential expansion between the metal array and the glass microlens substrate may lead to the bond between them failing at low temperatures. Although the coefficient of thermal expansion of epoxy is much greater than those of steel, brass or glass, the elasticity of the epoxy accommodates the dimensional changes without breakage: however, this can introduce a small amount of stress build-up.

It is well known that mechanical deformation causes focal ratio degradation (FRD) by the formation of microbends in the fibre (Clayton 1989). FRD is a non-conservation of *étendue* such that the focal ratio is broadened by propagation in the fibre. When mounting the fibre, the appropriate epoxy and tubing should be selected, and general care must be taken to minimize mechanical stress and avoid additional FRD (de Oliveira et al., 2005). This is straightforward at room temperature, but greater care must be taken in the choice of materials for use at low temperatures. When the fibre assembly is cooled to temperatures around -10 °C, the epoxy, tubing and ferrule will all shrink differentially, and this may cause the level of FRD to increase. There is other problem when the fibre assembly is warmed to around 20 °C and cooled to around -10 °C. The UV epoxy, currently used used to cement the metal and the glass may be damaged if the system will be submitted several times at big changes of temperature. In this case the system may detach in places due the thermal gradient.

Microholes array and support plate made with solidified EPOTEK represent a first step to change the metallic base for a polymeric base. The choice of the EPOTEK 301-2 is appropriate due to its excellent wicking properties and low shrinkage upon curing. This properties are very good to use in optical fibres system, so that, if it is possible to get plates adequate to machine with this epoxy we can get total compatible in the construction of the system.

Composite Material and Optical Fibres 401

displaying a minimum of burring; scarf, remaining in the holes, may be readily removed by

There are several advantages to the use of solidified epoxy as compared to brass, for example, in the fabrication and use of fibre support devices. Ease of machining and compatibility with other epoxies used to attach glass or silica, may be the most important of these advantages. Although the coefficient of thermal expansion of epoxy is much greater than that of steel or glass, Tab. 1, its elasticity accommodate thermally induced dimensional changes without breakage. This also avoids excessive stress associated with increases in FRD but, in principle, could be deleterious in compromising the critical positioning stability

**Material α CTE at 20 °C Units**  Brass 19 10-6 / °C Carbon Steel 10.8 10-6 / °C In ox Steel 17.3 10-6 / °C Quartz 0.59 10-6 / °C EPO-TEK 301-2 55 at 61 10-6 / °C

cleaning in an ultrasonic bath.

of optical fibres as the temperature varies.

**Figure 4.** Plate of EPO-TEK 301-2 solidified and machined

**Table 1.** Coefficient of Thermal Expansion of some materials

## **2.1. Epoxy solidified**

The epoxy EPO-TEK 301-2 has low viscosity and requires a container to constrain its flow until it is solidified. Generally aluminium has been used to make these containers but it is possible to use brass, plastic or acrylic. The complete curing process takes approximately three days at room temperature and when it is dry, it is transparent to visible light. To avoid bubbles and points of stress, the epoxy is prepared in a separate container inside a vacuum chamber. The correct amount is allowed to set in the container, which is placed inside a dry environment. Once cured, some thermal treatment may be necessary. Several kinds of blocks, cylinders and plates can be made to test the polishing qualities of these test pieces. The results are very encouraging with the hardness similar to acrylic resin. The Fig. 3 and 4 shows steps to obtain samples machined to manufacture blocks of epoxy solidified.

**Figure 3.** EPO-TEK 301-2 solidified, during the machining procedure

Machining quality is important as burrs inside the microholes may prevent the fibres from being threaded into the holes, or cause stress, or breakage, of the fibres. The quality of such microhole arrays inspected visually using a microscope, give very encouraging results displaying a minimum of burring; scarf, remaining in the holes, may be readily removed by cleaning in an ultrasonic bath.

400 Composites and Their Applications

**2.1. Epoxy solidified** 

system.

adequate to machine with this epoxy we can get total compatible in the construction of the

The epoxy EPO-TEK 301-2 has low viscosity and requires a container to constrain its flow until it is solidified. Generally aluminium has been used to make these containers but it is possible to use brass, plastic or acrylic. The complete curing process takes approximately three days at room temperature and when it is dry, it is transparent to visible light. To avoid bubbles and points of stress, the epoxy is prepared in a separate container inside a vacuum chamber. The correct amount is allowed to set in the container, which is placed inside a dry environment. Once cured, some thermal treatment may be necessary. Several kinds of blocks, cylinders and plates can be made to test the polishing qualities of these test pieces. The results are very encouraging with the hardness similar to acrylic resin. The Fig. 3 and 4

shows steps to obtain samples machined to manufacture blocks of epoxy solidified.

**Figure 3.** EPO-TEK 301-2 solidified, during the machining procedure

Machining quality is important as burrs inside the microholes may prevent the fibres from being threaded into the holes, or cause stress, or breakage, of the fibres. The quality of such microhole arrays inspected visually using a microscope, give very encouraging results There are several advantages to the use of solidified epoxy as compared to brass, for example, in the fabrication and use of fibre support devices. Ease of machining and compatibility with other epoxies used to attach glass or silica, may be the most important of these advantages. Although the coefficient of thermal expansion of epoxy is much greater than that of steel or glass, Tab. 1, its elasticity accommodate thermally induced dimensional changes without breakage. This also avoids excessive stress associated with increases in FRD but, in principle, could be deleterious in compromising the critical positioning stability of optical fibres as the temperature varies.

**Figure 4.** Plate of EPO-TEK 301-2 solidified and machined


**Table 1.** Coefficient of Thermal Expansion of some materials

Machining quality is important as burrs inside the microholes could prevent the fibres from entering the hole, cause stress, or breakage, of the optical fibres. The quality of the microholes array may be inspected visually using a binocular microscope and the results are often very satisfactory with minimal burring present. Swarf present in the holes is readily removed by cleaning in an ultrasonic bath. The Fig. 5 shows a sample of epoxy solidified with a microholes array.

Composite Material and Optical Fibres 403

analysis, polarized light is passed through a transparent sample or the body in question, and stress-induced or static stress changes in the light result in an interference-like pattern, which may be analysed to determine the principal stresses at each point within the body.

The basis for photo elastic measurement is a phenomenon of double refraction (also called artificial birefringence). There are two situations that may cause this phenomenon. Certain plastics exhibit the first situation when the sample of this type is subjected to an applied load, the resulting stress /strain field causes the molecules within the transparent material to have a preferred alignment. The second situation is exhibited by certain epoxies after dried and in this case the stress may be called static stress. In both situations the light wave vibrations have two preferred directions within the material and a wave of linearly polarised light entering the field is split into two waves which are linearly polarised at right angles to each other and which propagate with different velocities. That is, two rays travel along each an original line of propagation, and their electric vectors are mutually perpendicular. In fact, each vibration is collinear with one of the principal stress directions. (See Fig. 6.) Also, since the two waves travel at different velocities, a phase difference

**Figure 6.** Left: propagation of light through photo elastic models. Right: plane polariscope used to get

A very simple system to get qualitative images of the samples may be adapted with a transmission Polariscope, as shown in Fig. 6. The system uses a CCD camera to take the images. Stresses within solidified EPO-TEK 301-2 may be investigated with the use of the photo elasticity method whereby stress-induced birefringence is measured using polarized light. Static stress can be recorded as an interference pattern, which may be analysed to determine the principal stresses at each point within the material. Indeed, significant stress

This stress can be alleviated through thermal shock induced by warming the sample to 80 ºC for 30 min. Fig. 7 side right demonstrates the reduction in stress as the material is returned to room temperature. Of course, such experiments are only viable for transparent materials but they do give a warning that care must be taken in analysing the effects of thermally induced stress through measurement of fibre displacement in arrangements and FRD stress-induced.

information of the stress inside of the sample by analyse of the artificial birefringence.

induced birefringence is detected in such samples, as is shown in Fig.7 side left.

develops between then and by using certain optical elements.

**Figure 5.** Photograph of the microholes array in a sample of the EPO-TEK 301-2 solidified

After machined, this sample has a diameter of 48 mm and a thickness of 3 mm. This microholes array is matrix 30x30 holes spaced on a 1.0 mm pitch. The holes were machined using custom made drills with diameters of 0.60 mm and 0.21 mm. This produces a stepped hole, with the smaller diameter hole used for fibre positioning while the larger hole is used to accommodate a ferrule. The small holes are approximately 10 m larger than the fibre diameter to allow sufficient space for glue penetrates. The machining error in the position of the small holes was measured to be approximately 2 m.

## **2.2. Experimental stress analyses**

It is possible to use a very simple experiment of Photo elasticity method to evaluate the static stress in the plates of epoxy solidified. Classical two-dimensional photo elasticity is an optical experimental technique for determining stress fields in solids bodies. For a given analysis, polarized light is passed through a transparent sample or the body in question, and stress-induced or static stress changes in the light result in an interference-like pattern, which may be analysed to determine the principal stresses at each point within the body.

402 Composites and Their Applications

with a microholes array.

Machining quality is important as burrs inside the microholes could prevent the fibres from entering the hole, cause stress, or breakage, of the optical fibres. The quality of the microholes array may be inspected visually using a binocular microscope and the results are often very satisfactory with minimal burring present. Swarf present in the holes is readily removed by cleaning in an ultrasonic bath. The Fig. 5 shows a sample of epoxy solidified

**Figure 5.** Photograph of the microholes array in a sample of the EPO-TEK 301-2 solidified

the small holes was measured to be approximately 2 m.

**2.2. Experimental stress analyses** 

After machined, this sample has a diameter of 48 mm and a thickness of 3 mm. This microholes array is matrix 30x30 holes spaced on a 1.0 mm pitch. The holes were machined using custom made drills with diameters of 0.60 mm and 0.21 mm. This produces a stepped hole, with the smaller diameter hole used for fibre positioning while the larger hole is used to accommodate a ferrule. The small holes are approximately 10 m larger than the fibre diameter to allow sufficient space for glue penetrates. The machining error in the position of

It is possible to use a very simple experiment of Photo elasticity method to evaluate the static stress in the plates of epoxy solidified. Classical two-dimensional photo elasticity is an optical experimental technique for determining stress fields in solids bodies. For a given The basis for photo elastic measurement is a phenomenon of double refraction (also called artificial birefringence). There are two situations that may cause this phenomenon. Certain plastics exhibit the first situation when the sample of this type is subjected to an applied load, the resulting stress /strain field causes the molecules within the transparent material to have a preferred alignment. The second situation is exhibited by certain epoxies after dried and in this case the stress may be called static stress. In both situations the light wave vibrations have two preferred directions within the material and a wave of linearly polarised light entering the field is split into two waves which are linearly polarised at right angles to each other and which propagate with different velocities. That is, two rays travel along each an original line of propagation, and their electric vectors are mutually perpendicular. In fact, each vibration is collinear with one of the principal stress directions. (See Fig. 6.) Also, since the two waves travel at different velocities, a phase difference develops between then and by using certain optical elements.

**Figure 6.** Left: propagation of light through photo elastic models. Right: plane polariscope used to get information of the stress inside of the sample by analyse of the artificial birefringence.

A very simple system to get qualitative images of the samples may be adapted with a transmission Polariscope, as shown in Fig. 6. The system uses a CCD camera to take the images. Stresses within solidified EPO-TEK 301-2 may be investigated with the use of the photo elasticity method whereby stress-induced birefringence is measured using polarized light. Static stress can be recorded as an interference pattern, which may be analysed to determine the principal stresses at each point within the material. Indeed, significant stress induced birefringence is detected in such samples, as is shown in Fig.7 side left.

This stress can be alleviated through thermal shock induced by warming the sample to 80 ºC for 30 min. Fig. 7 side right demonstrates the reduction in stress as the material is returned to room temperature. Of course, such experiments are only viable for transparent materials but they do give a warning that care must be taken in analysing the effects of thermally induced stress through measurement of fibre displacement in arrangements and FRD stress-induced.

Composite Material and Optical Fibres 405

**Figure 8.** Samples of different composites at the centre and epoxy solidified at the borders

times less than the time required to polish a surface of brass of the same size.

high physical stability.

**3. Simple composite ferrule** 

though it has some degree of slow oxidation on its surface. This oxidation is evident from the slight colour change after a few weeks of exposure and manipulation, but still remains a

This composite has two physical characteristics very interesting for the construction of optical fibres holders. The first feature is its ability to sustain their polishing, with minimum quantities of abrasives during this procedure. In other words, when the composite is subjected to a polishing of high performance, the detachment of the refractory oxide nanoparticles reinforces gently the polishing process and increasing the efficiency of this procedure. The surface roughness measured in several samples, after high performance polishing was about 0.01 microns. Furthermore, the time for obtaining a polished surface with this quality is about 10

Mechanical deformation is a change of geometry of the optical fibre away from a straight cylinder. Large-scale bending, or macrobending is where the radius of the curvature of the bend is very large in comparison to the core diameter. On the other hand microbends are deformations of the cylindrical core shape, which are small, compared to the fibre diameter (Ransey 1988). It is well known that mechanical deformation causes FRD by the formations of microbends in the fibre (Clayton 1989). When mounting the fibre, the appropriate epoxy and tubing should be selected, and general care must be taken to minimize mechanical stress and avoid additional FRD. Currently steel ferrules tubes are used to prepare the extremities of the optical fibres for general purposes, in test lab or even as a part of some instrument. Although it is clear that inefficiencies can result in the use of metal ferrules

**Figure 7.** Left: sample before thermal shock. Right: same sample after thermal shock

## **2.3. Composite**

It is possible create composites using a mix of epoxy and several types of oxides in micro or nano-particle form. To avoid stress points and heterogeneous regions, the composite needs to be prepared using mixers of high speed. Ultrasonic chamber can be useful to ensure more uniformity to the mixture. Before the cure, this composite requires be subjected to a vacuum of 10-3 Torr to reduce bubbles inside of material. The mixture of EPO-TEK 301-2 with refractory material oxide in nano-powder, cured and submitted to a thermal treatment around 400 °C, produce a very interesting option instead simple epoxy solidified. The resulting material is more resistant and harder than EPO-TEK 301-2 and is found to be well suited to the fabrication of optical fibre arrays. Several different refractory material oxides in nano-powder may be used to produce different characteristics in this type of composite. So it is possible combine Zirconium oxide, Barium oxide, Silica oxide, Cerium oxide and others, Fig. 8, to obtain a material optimized to specific applications. The solidified mixture combines the beneficial characteristics of both the epoxy and the oxide; main factor its coefficient of thermal expansion is significantly lower than simple solidified epoxy; the exact value depending on the relative concentrations.

There are two important factors that consolidate the structure of this composite. The first is the process of cure of the liquid mixture. The second is the process of heating of the solid material obtained after the cure. The chemical reactions during the first process are limited by the time to reach the complete cure of the epoxy. Anyway, chemical analysis showed no evidence of endothermic or exothermic chemical reactions between oxides and epoxy. In fact, the materials involved in the mixture appear quite neutral. However, the heating procedure in temperatures around 400 C with slow cooling during 24 hours induces slight shrinkage on the material. Although the study still lacks depth, it is fairly simple to conclude that the structure undergoes some type of molecular rearrangement with some material loss and subsequent compaction. In fact this process carbonizes the external side of the solid material. To avoid total and destructive carbonization, both, the heating and cooling is done with the composite inside a steel container with refractory sand. After this procedure, the external part carbonized can be removed by machining process leaving the sample completely clean. The material thus obtained proves to be quite stable and resistant even

**Figure 8.** Samples of different composites at the centre and epoxy solidified at the borders

though it has some degree of slow oxidation on its surface. This oxidation is evident from the slight colour change after a few weeks of exposure and manipulation, but still remains a high physical stability.

This composite has two physical characteristics very interesting for the construction of optical fibres holders. The first feature is its ability to sustain their polishing, with minimum quantities of abrasives during this procedure. In other words, when the composite is subjected to a polishing of high performance, the detachment of the refractory oxide nanoparticles reinforces gently the polishing process and increasing the efficiency of this procedure. The surface roughness measured in several samples, after high performance polishing was about 0.01 microns. Furthermore, the time for obtaining a polished surface with this quality is about 10 times less than the time required to polish a surface of brass of the same size.

## **3. Simple composite ferrule**

404 Composites and Their Applications

**2.3. Composite** 

**Figure 7.** Left: sample before thermal shock. Right: same sample after thermal shock

value depending on the relative concentrations.

It is possible create composites using a mix of epoxy and several types of oxides in micro or nano-particle form. To avoid stress points and heterogeneous regions, the composite needs to be prepared using mixers of high speed. Ultrasonic chamber can be useful to ensure more uniformity to the mixture. Before the cure, this composite requires be subjected to a vacuum of 10-3 Torr to reduce bubbles inside of material. The mixture of EPO-TEK 301-2 with refractory material oxide in nano-powder, cured and submitted to a thermal treatment around 400 °C, produce a very interesting option instead simple epoxy solidified. The resulting material is more resistant and harder than EPO-TEK 301-2 and is found to be well suited to the fabrication of optical fibre arrays. Several different refractory material oxides in nano-powder may be used to produce different characteristics in this type of composite. So it is possible combine Zirconium oxide, Barium oxide, Silica oxide, Cerium oxide and others, Fig. 8, to obtain a material optimized to specific applications. The solidified mixture combines the beneficial characteristics of both the epoxy and the oxide; main factor its coefficient of thermal expansion is significantly lower than simple solidified epoxy; the exact

There are two important factors that consolidate the structure of this composite. The first is the process of cure of the liquid mixture. The second is the process of heating of the solid material obtained after the cure. The chemical reactions during the first process are limited by the time to reach the complete cure of the epoxy. Anyway, chemical analysis showed no evidence of endothermic or exothermic chemical reactions between oxides and epoxy. In fact, the materials involved in the mixture appear quite neutral. However, the heating procedure in temperatures around 400 C with slow cooling during 24 hours induces slight shrinkage on the material. Although the study still lacks depth, it is fairly simple to conclude that the structure undergoes some type of molecular rearrangement with some material loss and subsequent compaction. In fact this process carbonizes the external side of the solid material. To avoid total and destructive carbonization, both, the heating and cooling is done with the composite inside a steel container with refractory sand. After this procedure, the external part carbonized can be removed by machining process leaving the sample completely clean. The material thus obtained proves to be quite stable and resistant even

Mechanical deformation is a change of geometry of the optical fibre away from a straight cylinder. Large-scale bending, or macrobending is where the radius of the curvature of the bend is very large in comparison to the core diameter. On the other hand microbends are deformations of the cylindrical core shape, which are small, compared to the fibre diameter (Ransey 1988). It is well known that mechanical deformation causes FRD by the formations of microbends in the fibre (Clayton 1989). When mounting the fibre, the appropriate epoxy and tubing should be selected, and general care must be taken to minimize mechanical stress and avoid additional FRD. Currently steel ferrules tubes are used to prepare the extremities of the optical fibres for general purposes, in test lab or even as a part of some instrument. Although it is clear that inefficiencies can result in the use of metal ferrules submitted to low temperatures. Ferrules and inserts made with the composite described here, promises to be best option to handle the ends isolated of optical fibres.

Composite Material and Optical Fibres 407

**4. Microholes arrays using plates of composite** 

A system like that shown in section 1, Fig. 2, presented a problem in the past: This problem was the terrific facility to detach the glass substrate of the metal brass polished. Variations of temperature at long of time cause different expansion in the metal brass and the glass. After some time, the UV epoxy normally used to glue the microlens arrays with the microholes array, cannot support more the bonding between the metal brass plates due to the successive expansions and contractions caused by temperature variations. Experiments using plates made with epoxy solidified, Fig. 11 can resolve this kind of problem in the range of temperatures between –10 ºC and 22 ºC, typical of high altitude, ground-based observatories. Although the coefficient of thermal expansion of epoxy, around 60 x 10-6 in/in/°C, is much greater than that of brass metal, steel metal or glass, its elasticity accommodates dimensional changes thermally induced. This means less pressure on the optical fibre and consequently avoids increases in FRD associated with stress but, in principle, could be deleterious in compromising the critical positioning of fibres as the temperature varies. The ideal condition requires a material with elasticity controlled so as not to cause stress or shift the positioning of optical fibre under temperature gradients.

**Figure 11.** Microholes array device being prepared to be the input array of an IFU system

Notwithstanding the characteristics of this particular composite are still under study, this material was used successfully in the construction of devices for several fibres instruments. For example, we have used this composite to construct SIFS/IFU for the SOAR telescope in

## **3.1. Composite**

While there is no direct evidence for the deterioration in Focal Ratio Degradation (FRD) of optical fibres in severe temperature gradients, the fibre ends inserted into metallic containment devices such as steel ferrules can be a source of stress, and hence increased FRD at low temperatures. In such conditions, instruments using optical fibres may suffer some increase in FRD and consequent loss of system throughput when they are working in environments with significant thermal gradients, a common characteristic of ground-based observatories. It is possible to use careful methodologies that give absolute measurements of FRD to quantify the advantages of using epoxy-based composites rather than metals as support structures for the fibre ends. This is shown to be especially important in minimizing thermally induced stresses in the fibre terminations. Furthermore, by impregnating the composites with small cerium oxide particles the composite materials supply their own fine polishing grit, Fig. 9, which aids significantly to the optical quality of the finished product. Different types of inserts are possible, Fig. 10, depending only on the precision of the machining.

**Figure 9.** Microscopic photo of optical fibre inserted in a composite ferrule, after polishing procedure.

**Figure 10.** Inserts with optical fibres to be used in a fibres collector plate. Each insert can have several fibres.

## **4. Microholes arrays using plates of composite**

406 Composites and Their Applications

**3.1. Composite** 

submitted to low temperatures. Ferrules and inserts made with the composite described

While there is no direct evidence for the deterioration in Focal Ratio Degradation (FRD) of optical fibres in severe temperature gradients, the fibre ends inserted into metallic containment devices such as steel ferrules can be a source of stress, and hence increased FRD at low temperatures. In such conditions, instruments using optical fibres may suffer some increase in FRD and consequent loss of system throughput when they are working in environments with significant thermal gradients, a common characteristic of ground-based observatories. It is possible to use careful methodologies that give absolute measurements of FRD to quantify the advantages of using epoxy-based composites rather than metals as support structures for the fibre ends. This is shown to be especially important in minimizing thermally induced stresses in the fibre terminations. Furthermore, by impregnating the composites with small cerium oxide particles the composite materials supply their own fine polishing grit, Fig. 9, which aids significantly to the optical quality of the finished product. Different types of inserts are

**Figure 9.** Microscopic photo of optical fibre inserted in a composite ferrule, after polishing procedure.

**Figure 10.** Inserts with optical fibres to be used in a fibres collector plate. Each insert can have several fibres.

here, promises to be best option to handle the ends isolated of optical fibres.

possible, Fig. 10, depending only on the precision of the machining.

A system like that shown in section 1, Fig. 2, presented a problem in the past: This problem was the terrific facility to detach the glass substrate of the metal brass polished. Variations of temperature at long of time cause different expansion in the metal brass and the glass. After some time, the UV epoxy normally used to glue the microlens arrays with the microholes array, cannot support more the bonding between the metal brass plates due to the successive expansions and contractions caused by temperature variations. Experiments using plates made with epoxy solidified, Fig. 11 can resolve this kind of problem in the range of temperatures between –10 ºC and 22 ºC, typical of high altitude, ground-based observatories. Although the coefficient of thermal expansion of epoxy, around 60 x 10-6 in/in/°C, is much greater than that of brass metal, steel metal or glass, its elasticity accommodates dimensional changes thermally induced. This means less pressure on the optical fibre and consequently avoids increases in FRD associated with stress but, in principle, could be deleterious in compromising the critical positioning of fibres as the temperature varies. The ideal condition requires a material with elasticity controlled so as not to cause stress or shift the positioning of optical fibre under temperature gradients.

**Figure 11.** Microholes array device being prepared to be the input array of an IFU system

Notwithstanding the characteristics of this particular composite are still under study, this material was used successfully in the construction of devices for several fibres instruments. For example, we have used this composite to construct SIFS/IFU for the SOAR telescope in Chile, (de Oliveira et al. 2010) and FRODOspec/IFU for the Liverpool Telescope, (Macanhan et al. 2006).

Composite Material and Optical Fibres 409

In general, the schematic shown in Fig. 12 is the base of the entrance device of the lenslet IFU system. This device is much easier to be manufactured than the device described in section 1, Fig. 2. In fact, this new version does not require any precision in the holes confection on the composite plates. To obtain precision with the fibres position we have used a third plate called mask of precision, Fig. 13. This is a metal mask very thin obtained by a technique called electro formation. The mask obtained by this way may be configured to have holes with specifics diameters and pits, with error around 1 micron in the diameter and in the position of the holes. This technique may produce a metal nickel plate with 200 microns of thickness and the procedure is very cheap. Taking in account these facilities; the mask will define the precision of the fibres array. It is possible to obtain micro holes with the diameter exactly one or two microns larger than the diameter of the fibre used. For another hand, the diameter of the holes in the composite plates does not need to have any precision and may be much larger than the diameter of the fibre. Since that, the step holes with different diameters in the composite plates it is not more necessary, also will be not necessary to use ferrules and any kind of protection to the fibres. Eventually a device like as shown in the Fig. 13 need to be made under a microscope because the diameter of the fibre may be much small and the number of fibres

**Figure 13.** Entrance device during the assembling step, where the matrixes of holes in the composite

plate set and in the precision mask are populated with the optical fibres terminations.

involved at the assemble may be high.

## **4.1. Construction of microholes arrays systems**

To replace the brass metal or epoxy solidified and resolve the problems presented by both materials, we have used our composite to manufacture the parts of the microholes array device. The material composite obtained is less stressed and harder than EPOTEK 301-2 being a good choice to be used in optical fibres arrays. This material certainly has a combination of the characteristics from the epoxy and the refractory material oxides. The most important consequence of this combination is a coefficient of thermal expansion hither than metal brass but shorter than a simple epoxy solidified. The exactly number will depend of the relative concentration between the refractory material oxides and epoxy.

**Figure 12.** Schematic of the composite plates set to build the entrance device of lenslet IFU

In general, the schematic shown in Fig. 12 is the base of the entrance device of the lenslet IFU system. This device is much easier to be manufactured than the device described in section 1, Fig. 2. In fact, this new version does not require any precision in the holes confection on the composite plates. To obtain precision with the fibres position we have used a third plate called mask of precision, Fig. 13. This is a metal mask very thin obtained by a technique called electro formation. The mask obtained by this way may be configured to have holes with specifics diameters and pits, with error around 1 micron in the diameter and in the position of the holes. This technique may produce a metal nickel plate with 200 microns of thickness and the procedure is very cheap. Taking in account these facilities; the mask will define the precision of the fibres array. It is possible to obtain micro holes with the diameter exactly one or two microns larger than the diameter of the fibre used. For another hand, the diameter of the holes in the composite plates does not need to have any precision and may be much larger than the diameter of the fibre. Since that, the step holes with different diameters in the composite plates it is not more necessary, also will be not necessary to use ferrules and any kind of protection to the fibres. Eventually a device like as shown in the Fig. 13 need to be made under a microscope because the diameter of the fibre may be much small and the number of fibres involved at the assemble may be high.

408 Composites and Their Applications

**4.1. Construction of microholes arrays systems** 

et al. 2006).

epoxy.

Chile, (de Oliveira et al. 2010) and FRODOspec/IFU for the Liverpool Telescope, (Macanhan

To replace the brass metal or epoxy solidified and resolve the problems presented by both materials, we have used our composite to manufacture the parts of the microholes array device. The material composite obtained is less stressed and harder than EPOTEK 301-2 being a good choice to be used in optical fibres arrays. This material certainly has a combination of the characteristics from the epoxy and the refractory material oxides. The most important consequence of this combination is a coefficient of thermal expansion hither than metal brass but shorter than a simple epoxy solidified. The exactly number will depend of the relative concentration between the refractory material oxides and

**Figure 12.** Schematic of the composite plates set to build the entrance device of lenslet IFU

**Figure 13.** Entrance device during the assembling step, where the matrixes of holes in the composite plate set and in the precision mask are populated with the optical fibres terminations.

After assembled, the precision mask is glued against the composite plate and all set is immersed in EPOTEK 301-2 following the old procedure. To obtain the maximum throughput the surface of the fibres should be polished such that they are optically flat. This is the condition to attach the microlens array against the composite plate, Fig. 14 and Fig.15.

Composite Material and Optical Fibres 411

when the device is submitted at thermal gradients. More specifically, optical fibres arrays used in astronomic instruments need to resist low temperatures without displacement of the fibre position and without delamination problem between parts. Simples experiments show that the linear CTE assumes values between 20 and 40 x 10-6 / °C to 0 °C depending the concentration of the components. For example, a sample made with EPO-TEK 301-2, Barium oxide, Zircon oxide and Cerium oxide with proportions respectively 5:1:1:1, exhibits an α

Analysis of the Absolut Transmission in samples shows clearly that optical fibres inserted in brass or steel ferrules suffer increases in FRD when submitted to low temperatures. On the hand, the FRD increase in optical fibres inserted in ferrule made from EPO-TEK or in composite materials is minimised when submitted at the same negative variation of temperature. In fact, the result predicts a loss of around 10 per cent for the brass ferrules and around 3 per cent for the steel. Although it is clear that inefficiencies can result in the use of metal ferrules submitted to low temperatures, the losses are not easily quantifiable. The reason for this is that the ratio of the outer diameter of the fibre and the inside diameter of the ferrule defines the amount of epoxy between the ferrule and fibre. In the final analysis, this represents more or less compression in the fibre when the metal is compressed during

It is possible to do an experiment to observe the displacement of the fibres in an array of fibres constructed in the plates described in the section 4.2. An experimental array of 10 x 8 optical fibres is chosen as a representative test since it matches the base of the input array of IFUs as described before. A displacement is likely to occur with variations in temperature since the support material may suffer from some type of mechanical distortion. The experimental assembly consists of a support to hold the input array and to control thermal dissipation. A relay lens is used to project the image of the fibre array onto a CCD as a shown in the Fig. 16. The support to hold the array under examination (Fig. 17 and 18) is made of brass and had a canal for the introduction of liquid nitrogen. A continuous flux of dry nitrogen needs to be directed towards the surface of the input array to avoid condensation. Four small temperature sensors are cemented inside holes in the tested plate, close to the optical fibres. These sensors are necessary in order to test if the temperature along the plate reach thermalized state. A digital thermometer can be used to collect

In our experiment, another sensor was installed inside the brass support together with a special electrical resistor to allow for temperature control. The temperature of the input array was controlled over a range between 23 ºC and -10 ºC. Images of the illuminated optical fibres can be obtained for a set of temperatures within the allocated range. With these images it is possible to obtain information regarding the change in the position of each

fibre in the array. A simple algorithm may be used to process these results.

CTE around 30 x 10-6 1/°C.

the reduction of temperature.

information from the sensors.

**5.1. Tests on fibres in an array** 

**Figure 14.** SIFS/IFU microlens glued

The pre-polishing process starts with the removal of excess glue with 2000 grit emery paper. Initial lapping with 6 m diamond slurry on a copper plate and a second lapping with 1 m diamond slurry on a tin-lead plate is used until the complete removal of the precision mask. Without the metal mask, the material of the composite plate is self-abrasive enough to produce a polishing of high performance of the optical fibres on a chemical cloth. This procedure is a basic condition to attach the microlens array against the composite plate of fibre terminations.

## **5. Characterization**

The complete characterization of this composite may require several kinds of possible tests. However, applications with optical fibres in metrology involve analyses of displacement when the device is submitted at thermal gradients. More specifically, optical fibres arrays used in astronomic instruments need to resist low temperatures without displacement of the fibre position and without delamination problem between parts. Simples experiments show that the linear CTE assumes values between 20 and 40 x 10-6 / °C to 0 °C depending the concentration of the components. For example, a sample made with EPO-TEK 301-2, Barium oxide, Zircon oxide and Cerium oxide with proportions respectively 5:1:1:1, exhibits an α CTE around 30 x 10-6 1/°C.

Analysis of the Absolut Transmission in samples shows clearly that optical fibres inserted in brass or steel ferrules suffer increases in FRD when submitted to low temperatures. On the hand, the FRD increase in optical fibres inserted in ferrule made from EPO-TEK or in composite materials is minimised when submitted at the same negative variation of temperature. In fact, the result predicts a loss of around 10 per cent for the brass ferrules and around 3 per cent for the steel. Although it is clear that inefficiencies can result in the use of metal ferrules submitted to low temperatures, the losses are not easily quantifiable. The reason for this is that the ratio of the outer diameter of the fibre and the inside diameter of the ferrule defines the amount of epoxy between the ferrule and fibre. In the final analysis, this represents more or less compression in the fibre when the metal is compressed during the reduction of temperature.

## **5.1. Tests on fibres in an array**

410 Composites and Their Applications

**Figure 14.** SIFS/IFU microlens glued

**Figure 15.** FRODOS IFU microlens glued

fibre terminations.

**5. Characterization** 

Fig.15.

After assembled, the precision mask is glued against the composite plate and all set is immersed in EPOTEK 301-2 following the old procedure. To obtain the maximum throughput the surface of the fibres should be polished such that they are optically flat. This is the condition to attach the microlens array against the composite plate, Fig. 14 and

The pre-polishing process starts with the removal of excess glue with 2000 grit emery paper. Initial lapping with 6 m diamond slurry on a copper plate and a second lapping with 1 m diamond slurry on a tin-lead plate is used until the complete removal of the precision mask. Without the metal mask, the material of the composite plate is self-abrasive enough to produce a polishing of high performance of the optical fibres on a chemical cloth. This procedure is a basic condition to attach the microlens array against the composite plate of

The complete characterization of this composite may require several kinds of possible tests. However, applications with optical fibres in metrology involve analyses of displacement It is possible to do an experiment to observe the displacement of the fibres in an array of fibres constructed in the plates described in the section 4.2. An experimental array of 10 x 8 optical fibres is chosen as a representative test since it matches the base of the input array of IFUs as described before. A displacement is likely to occur with variations in temperature since the support material may suffer from some type of mechanical distortion. The experimental assembly consists of a support to hold the input array and to control thermal dissipation. A relay lens is used to project the image of the fibre array onto a CCD as a shown in the Fig. 16. The support to hold the array under examination (Fig. 17 and 18) is made of brass and had a canal for the introduction of liquid nitrogen. A continuous flux of dry nitrogen needs to be directed towards the surface of the input array to avoid condensation. Four small temperature sensors are cemented inside holes in the tested plate, close to the optical fibres. These sensors are necessary in order to test if the temperature along the plate reach thermalized state. A digital thermometer can be used to collect information from the sensors.

In our experiment, another sensor was installed inside the brass support together with a special electrical resistor to allow for temperature control. The temperature of the input array was controlled over a range between 23 ºC and -10 ºC. Images of the illuminated optical fibres can be obtained for a set of temperatures within the allocated range. With these images it is possible to obtain information regarding the change in the position of each fibre in the array. A simple algorithm may be used to process these results.

Composite Material and Optical Fibres 413

**Figure 18.** Schematic diagram of the holder showing the canal to flow the liquid nitrogen during the

fibre at the top/left is used as a position reference. The variations of vector's modulus during the temperature gradient are computed to produce a graph with sub pixel precision (Neal et al. 1997). In this section we present results of tests using fibre arrays submitted to negative temperature gradients. The purpose of these tests is to analyse how much the fibres in the array may be displaced from their original position as a function of the expansion of the material during the change of temperature. Figs. 20, 21 and 22 show the behaviour of arrays with 80 optical fibres when submitted to four temperature gradients. The accuracy calculated for this experiment was less than 0.2µm and the continue curve represents a fitted function.

procedure to decrease the temperature. The holder is made of brass.

**Figure 19.** Image of the optical fibres matrix illuminated and projected on the CCD.

**Figure 16.** Diagram of the experimental set up to take images from the optical fibre array. The CCD is installed in a translation stage to put the image of the optical fibre illuminated exactly in the centre of the CCD plate. The holder support is used to keep the fibre plate array fixed and to control thermal dissipation.

**Figure 17.** Schematic diagram of the holder where is fixed the fibre plate array.

## **5.2. Analyses of displacements of fibres in the array**

An image analysis by software then determines the centroid of each bright spotlight projected by each fibre from the array on the CCD. Several images like the sample shown in the Fig. 19 are used to determine an average value in the position of each bright spot light. This associates position vectors connecting each bright spotlight with the origin. The first

dissipation.

**Figure 16.** Diagram of the experimental set up to take images from the optical fibre array. The CCD is installed in a translation stage to put the image of the optical fibre illuminated exactly in the centre of the CCD plate. The holder support is used to keep the fibre plate array fixed and to control thermal

**Figure 17.** Schematic diagram of the holder where is fixed the fibre plate array.

An image analysis by software then determines the centroid of each bright spotlight projected by each fibre from the array on the CCD. Several images like the sample shown in the Fig. 19 are used to determine an average value in the position of each bright spot light. This associates position vectors connecting each bright spotlight with the origin. The first

**5.2. Analyses of displacements of fibres in the array** 

**Figure 18.** Schematic diagram of the holder showing the canal to flow the liquid nitrogen during the procedure to decrease the temperature. The holder is made of brass.

fibre at the top/left is used as a position reference. The variations of vector's modulus during the temperature gradient are computed to produce a graph with sub pixel precision (Neal et al. 1997). In this section we present results of tests using fibre arrays submitted to negative temperature gradients. The purpose of these tests is to analyse how much the fibres in the array may be displaced from their original position as a function of the expansion of the material during the change of temperature. Figs. 20, 21 and 22 show the behaviour of arrays with 80 optical fibres when submitted to four temperature gradients. The accuracy calculated for this experiment was less than 0.2µm and the continue curve represents a fitted function.

**Figure 19.** Image of the optical fibres matrix illuminated and projected on the CCD.

Composite Material and Optical Fibres 415

The bar graphs, demonstrates the distribution pattern of fibre positions as the temperature declines. It is possible to observe, the expansion of the EPO-TEK 301-2 epoxy material. The change in positions of the fibres amounts to ~12µm as the temperature approaches -10 ºC. The array made of brass almost reaches this value despite having a totally different molecular structure to the epoxy. An interesting result was obtained with the optical fibre array in composite as may be observed in the Fig. 23. The behaviour of the composite array at low temperatures, represented in the bar graphs, is less noticeable than that obtained for the brass and epoxy arrays. In fact, when submitted to -10 ºC the change of the positions at the fibres is less than 6µm. In the experimentation made with composite and brass plate samples, the temperature registered by all sensors on the plate was the same after some minutes and the error expected between the sensors would be around 0.2ºC. However, we noted variations of ~1.2C between the sensors in the experimentation with EPO-TEK plate. This may be explained by the fact that there are regions with different degrees of stress in the solidified EPO-TEK plate. These differences imply in a possible variation of thermal conductivity along the plate. As was shown in the section 2.3, stresses within solidified EPO-TEK 301-2 can be investigated with the use of the photo elasticity method whereby stress-induced birefringence is measured using polarised light. In fact it is quite common to

observe static stress in plates of EPO-TEK solidified.

temperatures, 10 min each.

**Figure 22.** Distribution pattern of the fibres array in composite submitted to 4 gradients of

**Number of Fibres**

The final conclusion for this experiment is that the composite epoxy material shows significant improvement and, in fact, has an even better performance than the brass or

0 2 4 6 8 10 12

0 2 4 6 8 10 12

0 2 4 6 8 10 12

0 2 4 6 8 10 12

**0C0 to -10C0**

**7C0 to 0C0**

**15C0 to 7C0**

**22C0 to 15C0**

**Displacement (m)**

**Figure 20.** Distribution pattern of the optical fibres array constructed in metal brass plate submitted to four gradients of temperatures, 10 min each.

**Figure 21.** Distribution pattern of the optical fibres array constructed in epoxy EPO-TEK 301-2 submitted to four gradients of temperatures, 10 min each.

The bar graphs, demonstrates the distribution pattern of fibre positions as the temperature declines. It is possible to observe, the expansion of the EPO-TEK 301-2 epoxy material. The change in positions of the fibres amounts to ~12µm as the temperature approaches -10 ºC. The array made of brass almost reaches this value despite having a totally different molecular structure to the epoxy. An interesting result was obtained with the optical fibre array in composite as may be observed in the Fig. 23. The behaviour of the composite array at low temperatures, represented in the bar graphs, is less noticeable than that obtained for the brass and epoxy arrays. In fact, when submitted to -10 ºC the change of the positions at the fibres is less than 6µm. In the experimentation made with composite and brass plate samples, the temperature registered by all sensors on the plate was the same after some minutes and the error expected between the sensors would be around 0.2ºC. However, we noted variations of ~1.2C between the sensors in the experimentation with EPO-TEK plate. This may be explained by the fact that there are regions with different degrees of stress in the solidified EPO-TEK plate. These differences imply in a possible variation of thermal conductivity along the plate. As was shown in the section 2.3, stresses within solidified EPO-TEK 301-2 can be investigated with the use of the photo elasticity method whereby stress-induced birefringence is measured using polarised light. In fact it is quite common to observe static stress in plates of EPO-TEK solidified.

414 Composites and Their Applications

four gradients of temperatures, 10 min each.

**Figure 20.** Distribution pattern of the optical fibres array constructed in metal brass plate submitted to

**Figure 21.** Distribution pattern of the optical fibres array constructed in epoxy EPO-TEK 301-2

0 2 4 6 8 10 12

0 2 4 6 8 10 12

**7 0**

**15 0**

**22 0**

0 2 4 6 8 10 12

0 2 4 6 8 10 12

**0 0**

**C to -10 0**

**C to 0 0 C**

**C to 7 0 C**

**C to 15 0**

**C**

**C**

**Displacement (m)**

submitted to four gradients of temperatures, 10 min each.

**Number of Fibres**

**Figure 22.** Distribution pattern of the fibres array in composite submitted to 4 gradients of temperatures, 10 min each.

The final conclusion for this experiment is that the composite epoxy material shows significant improvement and, in fact, has an even better performance than the brass or epoxy solidified. The chosen composite material (EPO-TEK 301-2 + zirconium oxide) retains the beneficial bonding properties of the epoxy while avoiding its thermal displacement properties.

Composite Material and Optical Fibres 417

To measure the FRD properties of an optical fibre it is necessary to illuminate the test fibre with an input beam of known focal ratio. Then the output beam can be measured and compared with the input beam from a pinhole with the same diameter as the fibre core to determine the amount of FRD produced by the test fibre. The result is a plot of absolute transmission against output focal ratio. The experimental apparatus used to achieve this is

Illumination is provided by a 1-to-1 telecentric optical system that produces an image from an extensive uniformly illuminated source. This source is fed by a stabilized halogen lamp and has a band pass filter to provide light at 525nm, and filter's bandwidth of 100nm. An iris diaphragm placed in the collimated beam can be used to select the input focal ratio. A microscope with a CCD and beam splitter, monitored by a TV may be inserted between the pinhole/fibre plane, to be sure that the pinhole or the test fibre occupies the same position. To ensure accurate alignment of the fibre with the optical axis of the camera, the fibre is mounted in a tip-tilt translation stage. To begin the experiment, the pinhole device and the CCD are positioned to give us a reference image. In the test sequence, the pinhole is replaced with the entrance of the test fibre and the CCD is illuminated by the exit of the test fibre to give a projected image of the fibre. A distance of 9 mm between the CCD and the pinhole (or the entrance of the fibre in test) was determined as the best position to obtain images for optimal analysis. Background exposures are necessary for subtraction from the test exposures to remove the effects of hot pixels and stray light. In our experiments all fibres were tested at wavelength of 525nm, (defined using a Schott glass VG14 colour filter,

We have developed a custom software package (DEGFOC 3.0) to reduce the fibre images and to obtain throughput energy curves. This software works with PC microcomputers in a WINDOWS environment. We found this to be an effective solution for use in the optical laboratory environment allowing for ease of analysis. The DEGFOC 3.0 package gives curves of enclosed energy as is shown in the Fig. 24 with the option to save the result in

Fibre throughputs are automatically determined as a function of output focal ratio. The first step is an estimation of the background level to be subtracted from the test exposures to remove the effects of hot pixels and stray light. The software then finds the image centre by calculating the weighted average of all pixels. It associates a radius with each pixel and calculates the eccentricity that, in the ideal case, should be zero. Our target here is to obtain the absolute transmission of the fibre at a particular input f-ratio. After establishing the distance between the fibre test and the CCD, the software defines concentric annuli centred on the fibre image. These are then used to define the efficiency over a range of f-numbers at the exit of the fibre, where each f-number value contains the summation of all energy emergent from the fibre. Each energy value is calculated by the number of counts within each annulus divided by total number of counts from the pinhole images. The limiting focal

ASCII format to be used in any graphic software, (eg: ORIGIN).

illustrated in Fig. 23.

 **50 nm filter's bandwidth**).

**5.4. Reduction software** 

## **5.3. FRD in optical fibres samples**

The mode dependent loss mechanisms are the causes of focal ratio degradation (FRD) in optical fibres, and are not often addressed by manufacturers. Mode dependent losses can be divided into two basic mechanisms. The first is waveguide scattering, which causes transfer of energy into loss modes by variations of the core diameter along the length of the fibre. The second is mechanical deformation. Mechanical deformation is a change of the geometry of the fibre away from a straight cylinder. Large scale bending, or macrobendings, is where the radius of curvature of the bend is very large in comparison to the core diameter. On the other hand, microbends are deformations of the cylindrical core shape, which are small, compared to the fibre diameter (Ransey 1988). It is well known that mechanical deformation causes FRD by the formation of microbends in the fibre (Clayton 1989). FRD is a nonconservation of *étendue* (or optical entropy) such that the focal ratio is broadened by propagation in the fibre. When mounting the fibre, the appropriate epoxy and, tubing should be selected and general care must be taken to minimise mechanical stress and avoid additional FRD.

**Figure 23.** Diagram of the apparatus used to measure FRD – 1, light source, band pass filter and light diffuser; 2, telecentric optical system with unit magnification; 3, adjustable iris diaphragm; 4, alignment plate with a pinhole and both extremities of the tested fibre; 5, *peltie*r device connected with the entrance of the optical fibre; 6, optical fibre; 7, exit of the optical fibre; 8, pinhole; 9, CCD; 10, xyz translation stage; 11, xyz translation stage; 12, microscope system; 13, CCD/lens; 14, beam splitter; 15, xyz translation stage

To measure the FRD properties of an optical fibre it is necessary to illuminate the test fibre with an input beam of known focal ratio. Then the output beam can be measured and compared with the input beam from a pinhole with the same diameter as the fibre core to determine the amount of FRD produced by the test fibre. The result is a plot of absolute transmission against output focal ratio. The experimental apparatus used to achieve this is illustrated in Fig. 23.

Illumination is provided by a 1-to-1 telecentric optical system that produces an image from an extensive uniformly illuminated source. This source is fed by a stabilized halogen lamp and has a band pass filter to provide light at 525nm, and filter's bandwidth of 100nm. An iris diaphragm placed in the collimated beam can be used to select the input focal ratio. A microscope with a CCD and beam splitter, monitored by a TV may be inserted between the pinhole/fibre plane, to be sure that the pinhole or the test fibre occupies the same position. To ensure accurate alignment of the fibre with the optical axis of the camera, the fibre is mounted in a tip-tilt translation stage. To begin the experiment, the pinhole device and the CCD are positioned to give us a reference image. In the test sequence, the pinhole is replaced with the entrance of the test fibre and the CCD is illuminated by the exit of the test fibre to give a projected image of the fibre. A distance of 9 mm between the CCD and the pinhole (or the entrance of the fibre in test) was determined as the best position to obtain images for optimal analysis. Background exposures are necessary for subtraction from the test exposures to remove the effects of hot pixels and stray light. In our experiments all fibres were tested at wavelength of 525nm, (defined using a Schott glass VG14 colour filter,  **50 nm filter's bandwidth**).

## **5.4. Reduction software**

416 Composites and Their Applications

**5.3. FRD in optical fibres samples** 

properties.

additional FRD.

translation stage

epoxy solidified. The chosen composite material (EPO-TEK 301-2 + zirconium oxide) retains the beneficial bonding properties of the epoxy while avoiding its thermal displacement

The mode dependent loss mechanisms are the causes of focal ratio degradation (FRD) in optical fibres, and are not often addressed by manufacturers. Mode dependent losses can be divided into two basic mechanisms. The first is waveguide scattering, which causes transfer of energy into loss modes by variations of the core diameter along the length of the fibre. The second is mechanical deformation. Mechanical deformation is a change of the geometry of the fibre away from a straight cylinder. Large scale bending, or macrobendings, is where the radius of curvature of the bend is very large in comparison to the core diameter. On the other hand, microbends are deformations of the cylindrical core shape, which are small, compared to the fibre diameter (Ransey 1988). It is well known that mechanical deformation causes FRD by the formation of microbends in the fibre (Clayton 1989). FRD is a nonconservation of *étendue* (or optical entropy) such that the focal ratio is broadened by propagation in the fibre. When mounting the fibre, the appropriate epoxy and, tubing should be selected and general care must be taken to minimise mechanical stress and avoid

**Figure 23.** Diagram of the apparatus used to measure FRD – 1, light source, band pass filter and light diffuser; 2, telecentric optical system with unit magnification; 3, adjustable iris diaphragm; 4, alignment plate with a pinhole and both extremities of the tested fibre; 5, *peltie*r device connected with the entrance of the optical fibre; 6, optical fibre; 7, exit of the optical fibre; 8, pinhole; 9, CCD; 10, xyz translation stage; 11, xyz translation stage; 12, microscope system; 13, CCD/lens; 14, beam splitter; 15, xyz

We have developed a custom software package (DEGFOC 3.0) to reduce the fibre images and to obtain throughput energy curves. This software works with PC microcomputers in a WINDOWS environment. We found this to be an effective solution for use in the optical laboratory environment allowing for ease of analysis. The DEGFOC 3.0 package gives curves of enclosed energy as is shown in the Fig. 24 with the option to save the result in ASCII format to be used in any graphic software, (eg: ORIGIN).

Fibre throughputs are automatically determined as a function of output focal ratio. The first step is an estimation of the background level to be subtracted from the test exposures to remove the effects of hot pixels and stray light. The software then finds the image centre by calculating the weighted average of all pixels. It associates a radius with each pixel and calculates the eccentricity that, in the ideal case, should be zero. Our target here is to obtain the absolute transmission of the fibre at a particular input f-ratio. After establishing the distance between the fibre test and the CCD, the software defines concentric annuli centred on the fibre image. These are then used to define the efficiency over a range of f-numbers at the exit of the fibre, where each f-number value contains the summation of all energy emergent from the fibre. Each energy value is calculated by the number of counts within each annulus divided by total number of counts from the pinhole images. The limiting focal

ratio that can propagate in the tested fibre is approximately f/2.2. Therefore we have defined f/2 to be the outer limit of the external annulus within which all of the light from the test fibre will be collected. The corresponding diameters of the annulus are converted to output focal ratios, multiplying them by the appropriate constant given by the distance between the fibre output end and the detector.

Composite Material and Optical Fibres 419

23 oC


obtained from one fibre with brass ferrule, in dry atmosphere, is shown in Fig. 25. These results show an increase in FRD when the brass ferrule experiences a cold temperature. The total variation observed in the hatched area is very strong and diminishes as the output focal ratio of the fibre is increased. An analysis of the results demonstrates that the loss of light at F/2.3 would be around 10 per cent. This degradation is caused, presumably, by the contraction of the brass ferrule with decreasing temperature causing compressive stress of the ferrule on the fibre. The error bars, of ± 1 per cent, together the average curves, were defined after repeating each experimentation at least six times. Some experimental uncertainty in the control of temperature causing small variations in the compression force on the ferrule/fibre and consequently cause small variations in the throughput of the sample. However is evident the presence of some dissipative process, which changes the borderline of the stress during the variations of temperature. Taking in account that the experiment is made with input focal ratio around the Numerical Aperture of the fibre

**Figure 25.** Performance of the optical fibre using brass ferrule. The ferrule was submitted to a negative

2.0 2.5 3.0 3.5 4.0

Such effects are critical to the design and implementation of fibre spectrographs. These results imply serious restrictions in the use of metal ferrules for optical fibres operating in ambient conditions that experience large changes of temperature typical of many

temperature gradient of 23 oC in a dry atmosphere. The gradient was obtained, reducing the temperature, 23 oC to -10 oC, in 30 min of interval time. Two extremes curves were measured in this

F/2.34 Output Focal Ratio (F/#)

observatories both during the night and throughout the year.

interval, producing the hatched area.

60

70

80

Absolute Transmission (per cent)

90

100

(F/2.27) there is the possibility that it is changing because the stress.

E lost ~ 10 per cent

**Figure 24.** Print screen of the windows to the DEGFOC software.

## **5.5. Temperature gradient & FRD in optical fibres**

In this experiment we have controlled the temperature of samples between –10 ºC and 22 ºC, typical of high altitude, ground-based observatories. To achieve this variation we have used a *Peltier* device coupled with a temperature sensor connected to an electronic controller. The end of the test fibre is placed in contact with the *Peltier* plate by a support, and to avoid problems with water condensation at low temperatures, the test ferrule is installed inside a plastic container with a glass window. A positive pressure of nitrogen gas is maintained using a flexible tube from a gas source. With these experimental arrangements it is possible to obtain images of the optical fibres with one of extremities inside a ferrule experiencing low temperatures without water condensation. This avoids the formation of ice at the end of the fibre that could attenuate the light at its termination and contaminate the results. Our aim is to measure the effect of constriction of the ferrule on the optical fibre caused by the gradient in temperature.

Plots of absolute transmission versus output focal ratio for three samples in four configurations are presented here. We have plotted graphs with the extremes curves obtained at room temperature of 23 ºC and at -10 ºC after a time interval of 30 min. chosen to stabilize the thermal effects between one measurement and next. The throughput graph obtained from one fibre with brass ferrule, in dry atmosphere, is shown in Fig. 25. These results show an increase in FRD when the brass ferrule experiences a cold temperature. The total variation observed in the hatched area is very strong and diminishes as the output focal ratio of the fibre is increased. An analysis of the results demonstrates that the loss of light at F/2.3 would be around 10 per cent. This degradation is caused, presumably, by the contraction of the brass ferrule with decreasing temperature causing compressive stress of the ferrule on the fibre. The error bars, of ± 1 per cent, together the average curves, were defined after repeating each experimentation at least six times. Some experimental uncertainty in the control of temperature causing small variations in the compression force on the ferrule/fibre and consequently cause small variations in the throughput of the sample. However is evident the presence of some dissipative process, which changes the borderline of the stress during the variations of temperature. Taking in account that the experiment is made with input focal ratio around the Numerical Aperture of the fibre (F/2.27) there is the possibility that it is changing because the stress.

418 Composites and Their Applications

fibre output end and the detector.

**Figure 24.** Print screen of the windows to the DEGFOC software.

**5.5. Temperature gradient & FRD in optical fibres** 

gradient in temperature.

ratio that can propagate in the tested fibre is approximately f/2.2. Therefore we have defined f/2 to be the outer limit of the external annulus within which all of the light from the test fibre will be collected. The corresponding diameters of the annulus are converted to output focal ratios, multiplying them by the appropriate constant given by the distance between the

In this experiment we have controlled the temperature of samples between –10 ºC and 22 ºC, typical of high altitude, ground-based observatories. To achieve this variation we have used a *Peltier* device coupled with a temperature sensor connected to an electronic controller. The end of the test fibre is placed in contact with the *Peltier* plate by a support, and to avoid problems with water condensation at low temperatures, the test ferrule is installed inside a plastic container with a glass window. A positive pressure of nitrogen gas is maintained using a flexible tube from a gas source. With these experimental arrangements it is possible to obtain images of the optical fibres with one of extremities inside a ferrule experiencing low temperatures without water condensation. This avoids the formation of ice at the end of the fibre that could attenuate the light at its termination and contaminate the results. Our aim is to measure the effect of constriction of the ferrule on the optical fibre caused by the

Plots of absolute transmission versus output focal ratio for three samples in four configurations are presented here. We have plotted graphs with the extremes curves obtained at room temperature of 23 ºC and at -10 ºC after a time interval of 30 min. chosen to stabilize the thermal effects between one measurement and next. The throughput graph

**Figure 25.** Performance of the optical fibre using brass ferrule. The ferrule was submitted to a negative temperature gradient of 23 oC in a dry atmosphere. The gradient was obtained, reducing the temperature, 23 oC to -10 oC, in 30 min of interval time. Two extremes curves were measured in this interval, producing the hatched area.

Such effects are critical to the design and implementation of fibre spectrographs. These results imply serious restrictions in the use of metal ferrules for optical fibres operating in ambient conditions that experience large changes of temperature typical of many observatories both during the night and throughout the year.

The throughput for samples with fibres inserted into epoxy ferrules and composite ferrules, in dry atmosphere, are shown for comparison in Figs. 26 and 27 using the same experimental procedures. Both graphs, present a very similar curves, with loss of light at F/2.34 around 2 per cent to the epoxy ferrule and 1 per cent to the composite ferrule. It seems that the loss of energy through stress-induced FRD effects is significantly less than that observed with the metal ferrule samples. The similarity of the epoxy and composite results imply that we are seeing similar effects due to the similar structure of both materials. In fact the composite material uses the same epoxy as a substrate. A natural compression happens during the cooling process, but does not produce a compressive stress of the brass ferrule on the fibre. The elastic properties of the epoxy may neutralize the mechanical stress on the fibre during the contraction process. The same error bars, of ± 1 per cent, were obtained after six repetitions of the experiment.

Composite Material and Optical Fibres 421

230C


20 ºC after machining to avoid anomalous results during the experimentations. However, this procedure may increase the intrinsic FRD of the fibre given that the material structure of the ferrule may suffer accommodation pressing the fibre extremity. On the other hand, small differences of size in the hatched area of lost energy between similar samples could be expected. Differences like that would be explained by the difficulty to quantify the total length of the fibre immersed in epoxy inside the ferrule. The procedure of inserting fibre and epoxy into the ferrule is virtually handmade. There is no way to accurately control the amount of epoxy into opaque ferrules, because it is not possible to visualize the level of epoxy. Exception perhaps for polished quartz ferrules. Obviously, the length of fibre immersed in epoxy defines the length that would be submitted at the stress from the ferrule

**Figure 27.** Performance of the optical fibre using composite ferrule. The ferrule was submitted to the same negative temperature gradient of the anterior experimentation using metal ferrule, steel ferrule

Output Focal Ratio (F/#) F/2.34

E lost ~ 1 per cent

2.0 2.5 3.0 3.5 4.0

There are two ways of surface preparations in optical fibres, cleaving and polishing. In general applications directed to scientific instrumentation require optical fibres with extremities polished. This is the way where it is possible to optimize the spot light from the optical fibre. Furthermore, all fibre connectors require polishing and high performance may be reached with special machines and dedicated procedures. Currently, polishing procedures

contraction.

and epoxy ferrule.

60

70

80

Absolute Transmission (per cent)

90

100

**6. Polishing substrate** 

**Figure 26.** Performance of the optical fibre using epoxy ferrule. The ferrule was submitted to the negative temperature gradient following the same conditions of the experimentation using metal ferrule.

In general, the variation in the FRD results obtained with different samples from the same optical fibres is ±~1 per cent because the noise of the measurements. Analyse of the throughput curves obtained at room temperature from the epoxy and composite ferrules is ~ 3 per cent less on average when comparing the same curve obtained from the metal ferrules samples. The explanation for this difference may be in the aging process of the epoxy and composite ferrules. Both samples were submitted to six thermal cycles, between 50 ºC and -

20 ºC after machining to avoid anomalous results during the experimentations. However, this procedure may increase the intrinsic FRD of the fibre given that the material structure of the ferrule may suffer accommodation pressing the fibre extremity. On the other hand, small differences of size in the hatched area of lost energy between similar samples could be expected. Differences like that would be explained by the difficulty to quantify the total length of the fibre immersed in epoxy inside the ferrule. The procedure of inserting fibre and epoxy into the ferrule is virtually handmade. There is no way to accurately control the amount of epoxy into opaque ferrules, because it is not possible to visualize the level of epoxy. Exception perhaps for polished quartz ferrules. Obviously, the length of fibre immersed in epoxy defines the length that would be submitted at the stress from the ferrule contraction.

**Figure 27.** Performance of the optical fibre using composite ferrule. The ferrule was submitted to the same negative temperature gradient of the anterior experimentation using metal ferrule, steel ferrule and epoxy ferrule.

#### **6. Polishing substrate**

420 Composites and Their Applications

ferrule.

60

70

80

Absolute Transmission (per cent)

90

100

obtained after six repetitions of the experiment.

E lost ~ 2 per cent

The throughput for samples with fibres inserted into epoxy ferrules and composite ferrules, in dry atmosphere, are shown for comparison in Figs. 26 and 27 using the same experimental procedures. Both graphs, present a very similar curves, with loss of light at F/2.34 around 2 per cent to the epoxy ferrule and 1 per cent to the composite ferrule. It seems that the loss of energy through stress-induced FRD effects is significantly less than that observed with the metal ferrule samples. The similarity of the epoxy and composite results imply that we are seeing similar effects due to the similar structure of both materials. In fact the composite material uses the same epoxy as a substrate. A natural compression happens during the cooling process, but does not produce a compressive stress of the brass ferrule on the fibre. The elastic properties of the epoxy may neutralize the mechanical stress on the fibre during the contraction process. The same error bars, of ± 1 per cent, were

**Figure 26.** Performance of the optical fibre using epoxy ferrule. The ferrule was submitted to the negative temperature gradient following the same conditions of the experimentation using metal

Output Focal Ratio (F/#) F/2.34

In general, the variation in the FRD results obtained with different samples from the same optical fibres is ±~1 per cent because the noise of the measurements. Analyse of the throughput curves obtained at room temperature from the epoxy and composite ferrules is ~ 3 per cent less on average when comparing the same curve obtained from the metal ferrules samples. The explanation for this difference may be in the aging process of the epoxy and composite ferrules. Both samples were submitted to six thermal cycles, between 50 ºC and -

2.0 2.5 3.0 3.5 4.0

230C


There are two ways of surface preparations in optical fibres, cleaving and polishing. In general applications directed to scientific instrumentation require optical fibres with extremities polished. This is the way where it is possible to optimize the spot light from the optical fibre. Furthermore, all fibre connectors require polishing and high performance may be reached with special machines and dedicated procedures. Currently, polishing procedures to optical fibres are based on very delicate glass paper or lapping discs soaked in abrasive liquid solutions. Often, this kind of liquid abrasive is very expensive taking in account your composition based in sophisticated chemistry keeping micro diamonds in suspension. Other options, considers abrasive silica and aluminium oxide mixed with oil solution or water solution. A very interesting application for the composite described here is its use as a highperformance abrasive disc to polish optical fibres.

Composite Material and Optical Fibres 423

The motivation of this work was to test the performance of optical fibres inserted in ferrules made with different materials at low temperatures. The problem of finding a material best suited to securing fibres for astronomical spectrographs to cope with thermal stresses, FRD minimization and the need to achieve adequate polishing finish led us to investigate the use of composite materials. As has already been demonstrated, epoxies can be used not only as a means of holding fibres within structures (slit blocks, fibre arrays etc.) but also as a material to fabricate the structures themselves. The properties that require investigation in this context are CTE matching, machinability, bonding to glass and ease of polishing. In this context we have made several samples to evaluate FRD performance and position

displacement of the inserted fibres when submitted to low temperatures.

*Laboratório Nacional de Astrofísica / Ministério da Ciência Tecnologia e Inovação, Brazil* 

This work was financially supported by the FAPESP project no. 1999/03744-1 and CNPq project 62.0053/01-1- PADCT III/ Milenio. We wish to thank the staff of the Laboratório

Clayton, C. A. (1989). The Implications of Image Scrambling and Focal Ratio Degradation in Fibre Optics on the Design of Astronomical Instrumentation, Astronomy and

de Oliveira, A. C. et al. (2002). The Eucalyptus Spectrograph, Proceedings of SPIE Instrument Design and Performance for Optical/Infrared Ground-based Telescopes, pp.

de Oliveira, A. C. et al. (2005). Studying Focal Ratio Degradation of Optical Fibres with a Core Size of 50μm for Astronomy, Mon. Not. R. Astron. Soc., Vol. 356, No. 3, (October

de Oliveira, A. C. et al. (2010). The SOAR Integral Field Unit Spectrograph Optical Design and IFU Implementation, Proceedings of SPIE Modern Technologies in Space- and Ground-based Telescopes and Instrumentation, pp. 77394S-1-77394S-12, San Diego,

Ransey, L. W. (1988). Focal Ratio Degradation in Optical Fibers of Astronomical Interest, In: *Fiber Optics in Astronomy,* Samuel C. Barden, pp. 26-40, Astronomical Society of the

Astrophysics, Vol. 213, No. 1-2, (April 1989), pp. 502-515, ISSN 0004-6361

1417-1428, Waikoloa, Hawaii, USA, August 25-28, 2002

Pacific, ISBN 0-937707-20-1, San Francisco, California, USA

2004), pp. 1079-1087, ISSN 00358711

California, USA, June 27, 2010

**7. Conclusion** 

**Author details** 

**Acknowledgement** 

**8. References** 

Nacional de Astrofísica/ MCT.

Antonio C. de Oliveira and Ligia S. de Oliveira

## **6.1. Abrasive discs of composite to polish optical fibres**

It is possible to fabricate composite discs, controlling the abrasive capacity through the correct choice of oxide and quantity mixed with epoxy. There are several manufacturers of oxide refractory with high purity such that it is possible to compose a complete grid of polishing discs. We can consider two major advantages in the use of polishing discs manufactured with composite: The first lies in the fact that the entire polishing process can be done using distilled water only. The second advantage is that after the polishing procedure, the disc can be restored to its original flatness and completely cleaned by machining process. The efficiency of this composite disc to polish optical fibres is based in the fact that some of the oxides of the mixture are naturally abrasives. Materials like cerium oxide or silica oxide can be prepared in liquid solutions abrasives and has been used for a long time in polishing procedures of lenses and other optical devices. Discs of composite can be made in any size and can easily be adapted in the rotation device of polishing machine. Fig. 28 shows an array of optical fibres polished using discs of composite.

**Figure 28.** Microscopic photo of part of the optical fibres array, after polishing procedure, using discs of composite containing cerium oxide.

## **7. Conclusion**

422 Composites and Their Applications

composite.

composite containing cerium oxide.

performance abrasive disc to polish optical fibres.

**6.1. Abrasive discs of composite to polish optical fibres** 

to optical fibres are based on very delicate glass paper or lapping discs soaked in abrasive liquid solutions. Often, this kind of liquid abrasive is very expensive taking in account your composition based in sophisticated chemistry keeping micro diamonds in suspension. Other options, considers abrasive silica and aluminium oxide mixed with oil solution or water solution. A very interesting application for the composite described here is its use as a high-

It is possible to fabricate composite discs, controlling the abrasive capacity through the correct choice of oxide and quantity mixed with epoxy. There are several manufacturers of oxide refractory with high purity such that it is possible to compose a complete grid of polishing discs. We can consider two major advantages in the use of polishing discs manufactured with composite: The first lies in the fact that the entire polishing process can be done using distilled water only. The second advantage is that after the polishing procedure, the disc can be restored to its original flatness and completely cleaned by machining process. The efficiency of this composite disc to polish optical fibres is based in the fact that some of the oxides of the mixture are naturally abrasives. Materials like cerium oxide or silica oxide can be prepared in liquid solutions abrasives and has been used for a long time in polishing procedures of lenses and other optical devices. Discs of composite can be made in any size and can easily be adapted in the rotation device of polishing machine. Fig. 28 shows an array of optical fibres polished using discs of

**Figure 28.** Microscopic photo of part of the optical fibres array, after polishing procedure, using discs of

The motivation of this work was to test the performance of optical fibres inserted in ferrules made with different materials at low temperatures. The problem of finding a material best suited to securing fibres for astronomical spectrographs to cope with thermal stresses, FRD minimization and the need to achieve adequate polishing finish led us to investigate the use of composite materials. As has already been demonstrated, epoxies can be used not only as a means of holding fibres within structures (slit blocks, fibre arrays etc.) but also as a material to fabricate the structures themselves. The properties that require investigation in this context are CTE matching, machinability, bonding to glass and ease of polishing. In this context we have made several samples to evaluate FRD performance and position displacement of the inserted fibres when submitted to low temperatures.

## **Author details**

Antonio C. de Oliveira and Ligia S. de Oliveira *Laboratório Nacional de Astrofísica / Ministério da Ciência Tecnologia e Inovação, Brazil* 

## **Acknowledgement**

This work was financially supported by the FAPESP project no. 1999/03744-1 and CNPq project 62.0053/01-1- PADCT III/ Milenio. We wish to thank the staff of the Laboratório Nacional de Astrofísica/ MCT.

## **8. References**

	- Macanhan, V. B. P. et al. (2006). FRODOSPEC Integral Fibre Unit, Proceedings of SAB XXXII Reunião da Sociedade Astronômica Brasileira, pp. 194-195, Atibaia, São Paulo, Brasil, August 3, 2006

August 3, 2006

Macanhan, V. B. P. et al. (2006). FRODOSPEC Integral Fibre Unit, Proceedings of SAB XXXII Reunião da Sociedade Astronômica Brasileira, pp. 194-195, Atibaia, São Paulo, Brasil,

## *Edited by Ning Hu*

Composites are a class of material, which receives much attention not only because it is on the cutting edge of active material research fields due to appearance of many new types of composites, e.g., nanocomposites and bio-medical composites, but also because there are a great deal of promise for its potential applications in various industries ranging from aerospace to construction due to its various outstanding properties. This book mainly describes some potential applications and the related properties of various composites by focusing on the following several topics: health or integrity monitoring techniques of composites structures, bio-medical composites and their applications in dental or tissue materials, natural fiber or mineral filler reinforced composites and their property characterization, catalysts composites and their applications, and some other potential applications of fibers or composites as sensors, etc. This book has been divided into five sections to cover the above contents.

Composites and Their Applications

Composites and Their

Applications

*Edited by Ning Hu*

Photo by wahahaz / iStock