**2.3. Electrophoretic impregnation of porous anodizing layer by synthesized TiO2 nanoparticles**

#### *2.3.1. Synthesis of TiO2 nanoparticles*

**Figure 3.** SEM observations associated with 3D roughness profiles: (a) sample after mechanical polishing and (b) after

mechanical and electrochemical polishing.

128 Electrophoresis - Life Sciences Practical Applications

**Figure 4.** Experimental setup of anodizing.

In order to prepare the TiO<sup>2</sup> nanopowder, 10 ml of ethanol (C<sup>2</sup> H5 OH), 10 ml of acetic acid (CH<sup>3</sup> COOH), 400 μL of hydrochloric acid (HCL) were used as catalysts, and 10 ml of titanium tetraisopropoxide precursor(Ti (OCH(CH<sup>3</sup> ) 2 )4 ) were mixed in the indicated order. The mixture was stirred for 30 min at a constant speed of 200 rpm to obtain the TiO<sup>2</sup> sol. Then the resulting sol was introduced into the autoclave (**Figure 7**) heated up to 243°C and pressurized to overcome the critical point of ethanol (T<sup>c</sup> = 243°C, P<sup>c</sup> = 63 bar). After maintaining temperature at 243°C for 1 h, the sol-gelation occurred. To evacuate the interstitial solvent, depressurization for 1 h down to room temperature was conducted with nitrogen gas. Finally, titanium aerogel was obtained.

**Figure 8** indicates the sol-gel TiO<sup>2</sup> fabrication diagram.

#### *2.3.2. Structural and morphological investigations of TiO2 nanopowder*

Fourier-transform infrared (FTIR) spectroscopy was used to identify the functional groups presented in the as-synthesized TiO2 nanopowder. The FTIR absorbance spectra were given

**Figure 5.** The approach for the conduct of the two-step anodization.

**Figure 6.** SEM images of anodic layer elaborated on th Al5754 aluminum alloy (a) in phosphoric bath (H<sup>3</sup> PO<sup>4</sup> 8%, U = 195 V, T = −1.5° C and t = 4 h) and (b) cross section of the anodizing layer [5].

2θ (degree) of 25.23, 37.81, and 48.14 degree were indexed as (101), (004), and (200) planes

((PDF) # 00-021-1272).

thin films, *k* as a constant (=0.89), *λ* as the wavelength of

which matches well the reported data for TiO2

has been calculated using Scherer's equation [9].

X-ray (CuKα = 1.5406 Å), *β* as the true half-peak width, and *θ* as the half diffraction angle of the centroid of the peak in degree. Any contributions to broadening due to non-uniform stress were neglected and the instrumental line width in the XRD apparatus was subtracted. The

**Figure 11 (a**–**b)** shows the SEM micrographs that describe the morphology of the as-synthe-

spherical clusters. In addition, the expertise of **Figure 11b** suggested that the spherical-shaped

 *nanopowder by SEM and TEM*

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nanopowder. As it can be observed from the **Figure 11a**, the powder consists of

of anatase phase TiO2

**Figure 8.** The sol-gel TiO<sup>2</sup>

The grain size of TiO<sup>2</sup>

sized TiO2

With D as the crystallite size of TiO<sup>2</sup>

*2.3.3. Characterization of synthesized TiO2*

calculated crystallite size of the anatase phase was about 20 nm.

fabrication diagram.

**Figure 7.** PARR autoclave-type pressure reactor and solvent removal system.

in **Figure 9**. A wide band ranging between 400 and 900 cm−1 was attributed to Ti-O stretching vibrations [6]. In the medium wavenumber range, the bands at 1300–1800 cm−1 were attributed to ν[C=C, C=O] and δ CH<sup>3</sup> vibrations corresponding to the organic residues [7]. It was believed that a broad band at ds 3500 cm−1 corresponds to the surface-adsorbed water [8]. In fact, the energy dispersive X-ray (EDX) spectra shown in **Figure 11** indicates the presence of an oxygen excess which can be attributed to the adsorbed hydroxide groups on the surface of TiO2 nanoparticles.

The XRD pattern of TiO<sup>2</sup> nanopowder is shown in **Figure 10**. The obvious diffraction peaks of anatase TiO2 structure in the range of resolution of XRD were well defined which indicated the good crystallinity of the synthesized TiO<sup>2</sup> nanopowder. In fact, the diffraction peaks at Improving Tribological Behavior of Porous Anodic Film by Electrophoretic Impregnation by… http://dx.doi.org/10.5772/intechopen.75782 131

**Figure 8.** The sol-gel TiO<sup>2</sup> fabrication diagram.

in **Figure 9**. A wide band ranging between 400 and 900 cm−1 was attributed to Ti-O stretching vibrations [6]. In the medium wavenumber range, the bands at 1300–1800 cm−1 were attrib-

**Figure 6.** SEM images of anodic layer elaborated on th Al5754 aluminum alloy (a) in phosphoric bath (H<sup>3</sup>

U = 195 V, T = −1.5° C and t = 4 h) and (b) cross section of the anodizing layer [5].

130 Electrophoresis - Life Sciences Practical Applications

**Figure 7.** PARR autoclave-type pressure reactor and solvent removal system.

believed that a broad band at ds 3500 cm−1 corresponds to the surface-adsorbed water [8]. In fact, the energy dispersive X-ray (EDX) spectra shown in **Figure 11** indicates the presence of an oxygen excess which can be attributed to the adsorbed hydroxide groups on the surface of

vibrations corresponding to the organic residues [7]. It was

nanopowder. In fact, the diffraction peaks at

PO<sup>4</sup> 8%,

nanopowder is shown in **Figure 10**. The obvious diffraction peaks of

structure in the range of resolution of XRD were well defined which indicated

uted to ν[C=C, C=O] and δ CH<sup>3</sup>

the good crystallinity of the synthesized TiO<sup>2</sup>

nanoparticles.

The XRD pattern of TiO<sup>2</sup>

TiO2

anatase TiO2

2θ (degree) of 25.23, 37.81, and 48.14 degree were indexed as (101), (004), and (200) planes of anatase phase TiO2 which matches well the reported data for TiO2 ((PDF) # 00-021-1272).

The grain size of TiO<sup>2</sup> has been calculated using Scherer's equation [9].

With D as the crystallite size of TiO<sup>2</sup> thin films, *k* as a constant (=0.89), *λ* as the wavelength of X-ray (CuKα = 1.5406 Å), *β* as the true half-peak width, and *θ* as the half diffraction angle of the centroid of the peak in degree. Any contributions to broadening due to non-uniform stress were neglected and the instrumental line width in the XRD apparatus was subtracted. The calculated crystallite size of the anatase phase was about 20 nm.

#### *2.3.3. Characterization of synthesized TiO2 nanopowder by SEM and TEM*

**Figure 11 (a**–**b)** shows the SEM micrographs that describe the morphology of the as-synthesized TiO2 nanopowder. As it can be observed from the **Figure 11a**, the powder consists of spherical clusters. In addition, the expertise of **Figure 11b** suggested that the spherical-shaped

**Figure 9.** FTIR spectra of as-prepared TiO<sup>2</sup> nanopowder.

TiO2 particles are hollow and composed of nanosized TiO2 anatase. The TiO2 nanoparticles show an even distribution with a mean size of about 20 nm.

Furthermore, the crystalline structure of TiO<sup>2</sup> nanopowder was investigated by transmission electronic microscopy (TEM) (**Figure 12**) observation in order to estimate the primary TiO<sup>2</sup> crystallite. The TEM images of TiO<sup>2</sup> nanopowder are shown in **Figure 12 (a**–**b)**. As shown

in **Figure 12a**, the primary TiO<sup>2</sup>

**Figure 11.** SEM images of synthesized TiO2

TiO2

sition process (EPD).

cates that the synthesized TiO2

satisfactory agreement with the SEM results.

crystallite had a diameter of about 10–20 nm which was in a

nanopowder (a) Spherical clusters and (b) nanosized TiO2

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nanopar-

anatase.

nanoparticles

The local crystal structure of anatase was confirmed by selected area electron diffraction (SAED) technique. One SAED ring diffraction pattern with marked Miller indices of anatase

ticles seemed adequate to be used for the pores filling using an adopted electrophoretic depo-

shows peaks for titanium (Ti) and oxygen (O) elements. There is no trace of any other impurities could be seen within the detection limit of the EDX as presented in **Figure 11**. This indi-

nanopowder was qualified with a high purity.

or more. Thus from the morphological studies, we can say that the synthesized TiO<sup>2</sup>

Energy dispersive X-ray (EDX) spectrometry analysis of the synthetized TiO<sup>2</sup>

 nanopowder (JCPDS card no. 21-1272) is given in **Figure 12b**. The ring pattern confirmed that synthesized nanopowder is polycrystalline with constituent crystallites of about 10 nm

**Figure 10.** X-ray diffraction pattern of TiO<sup>2</sup> nanopowder synthesized by sol-gel process.

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**Figure 11.** SEM images of synthesized TiO2 nanopowder (a) Spherical clusters and (b) nanosized TiO2 anatase.

TiO2

particles are hollow and composed of nanosized TiO2

nanopowder.

electronic microscopy (TEM) (**Figure 12**) observation in order to estimate the primary TiO<sup>2</sup>

nanopowder synthesized by sol-gel process.

show an even distribution with a mean size of about 20 nm.

Furthermore, the crystalline structure of TiO<sup>2</sup>

crystallite. The TEM images of TiO<sup>2</sup>

**Figure 10.** X-ray diffraction pattern of TiO<sup>2</sup>

**Figure 9.** FTIR spectra of as-prepared TiO<sup>2</sup>

132 Electrophoresis - Life Sciences Practical Applications

anatase. The TiO2

nanopowder was investigated by transmission

nanopowder are shown in **Figure 12 (a**–**b)**. As shown

nanoparticles

in **Figure 12a**, the primary TiO<sup>2</sup> crystallite had a diameter of about 10–20 nm which was in a satisfactory agreement with the SEM results.

The local crystal structure of anatase was confirmed by selected area electron diffraction (SAED) technique. One SAED ring diffraction pattern with marked Miller indices of anatase TiO2 nanopowder (JCPDS card no. 21-1272) is given in **Figure 12b**. The ring pattern confirmed that synthesized nanopowder is polycrystalline with constituent crystallites of about 10 nm or more. Thus from the morphological studies, we can say that the synthesized TiO<sup>2</sup> nanoparticles seemed adequate to be used for the pores filling using an adopted electrophoretic deposition process (EPD).

Energy dispersive X-ray (EDX) spectrometry analysis of the synthetized TiO<sup>2</sup> nanoparticles shows peaks for titanium (Ti) and oxygen (O) elements. There is no trace of any other impurities could be seen within the detection limit of the EDX as presented in **Figure 11**. This indicates that the synthesized TiO2 nanopowder was qualified with a high purity.

**Figure 12.** Characterization of synthesized nanopowder by SEM (a) Size of primary crystallites and (b) SAED ring diffraction pattern with marked Miller indices of anatase TiO2 nanopowder.

#### *2.3.4. Electrophoretic impregnation of anodizing layer by a synthesized TiO2 nanoparticle*

#### *2.3.4.1. Preparation of the TiO2 nanoparticles suspension*

#### *2.3.4.1.1. Effect of ultrasound on the dispersion of nanoparticles*

According to preliminary studies, 0.05 g/100 ml of TiO<sup>2</sup> nanoparticles was chosen as the optimal concentration to achieve the EPD process. To do so, a stock solution (mother solution) that comprises mixing 0.05 g of TiO<sup>2</sup> with 100 ml of distilled water was prepared. The mixture was then magnetically stirred for 15 min. To investigate the effect of ultrasound on the dispersion of nanoparticles, the mother solution was subjected to ultrasonic various times (0, 5, 10, 20, 30, 60, and 90 min) (see **Figure 13**). According to the optical properties of the suspension, the absorbance increases with the increase of ultrasonic time. This indicates good dispersion of nanoparticles of TiO2 in the aqueous suspension. Based on the findings shown in **Figure 14**, the use of ultrasound leads to the break of the clusters of TiO<sup>2</sup> into smaller agglomerates and aggregates. Agglomerated particles were thus eroded and divided by the collisions between particles [10–12]. A slight difference was observed between 60 and 90 min. So, 1 hour of ultrasonication seemed to be considered as an optimal setting for the preparation of a well-dispersed TiO<sup>2</sup> suspension.

*2.3.4.1.2. Effect of PAA amount on the zeta potential*

reasonably stable dispersion [13].

**Figure 14.** FEG-SEM images of TiO<sup>2</sup>

**Figure 13.** Absorbance spectra of the TiO<sup>2</sup>

of wavelength.

/poly(acrylic acid) (PAA) suspensions at different polymer content was mea-

nanoparticles: (a) without ultrasound and (b) after 90 min of ultrasound.

nanoparticles dispersed in water with and without ultrasound as a function

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135

sured on the basis of zeta potential measurements by means of the electrophoretic mobility. A zeta potential (ζ) of at least 30 mv (positive or negative) was normally required to achieve

**Figure 15** presents the effect of the polymer content on the stability of the suspensions at initial pH (6). According to **Figure 10**, the addition of PAA resulted in a good dispersion of the

Stability of TiO<sup>2</sup>

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**Figure 13.** Absorbance spectra of the TiO<sup>2</sup> nanoparticles dispersed in water with and without ultrasound as a function of wavelength.

**Figure 14.** FEG-SEM images of TiO<sup>2</sup> nanoparticles: (a) without ultrasound and (b) after 90 min of ultrasound.

#### *2.3.4.1.2. Effect of PAA amount on the zeta potential*

*2.3.4. Electrophoretic impregnation of anodizing layer by a synthesized TiO2*

*2.3.4.1.1. Effect of ultrasound on the dispersion of nanoparticles*

diffraction pattern with marked Miller indices of anatase TiO2 nanopowder.

According to preliminary studies, 0.05 g/100 ml of TiO<sup>2</sup>

ultrasound leads to the break of the clusters of TiO<sup>2</sup>

 *nanoparticles suspension*

mal concentration to achieve the EPD process. To do so, a stock solution (mother solution) that

**Figure 12.** Characterization of synthesized nanopowder by SEM (a) Size of primary crystallites and (b) SAED ring

then magnetically stirred for 15 min. To investigate the effect of ultrasound on the dispersion of nanoparticles, the mother solution was subjected to ultrasonic various times (0, 5, 10, 20, 30, 60, and 90 min) (see **Figure 13**). According to the optical properties of the suspension, the absorbance increases with the increase of ultrasonic time. This indicates good dispersion of nanopar-

Agglomerated particles were thus eroded and divided by the collisions between particles [10–12]. A slight difference was observed between 60 and 90 min. So, 1 hour of ultrasonication seemed

to be considered as an optimal setting for the preparation of a well-dispersed TiO<sup>2</sup>

in the aqueous suspension. Based on the findings shown in **Figure 14**, the use of

*2.3.4.1. Preparation of the TiO2*

134 Electrophoresis - Life Sciences Practical Applications

comprises mixing 0.05 g of TiO<sup>2</sup>

ticles of TiO2

 *nanoparticle*

nanoparticles was chosen as the opti-

into smaller agglomerates and aggregates.

suspension.

with 100 ml of distilled water was prepared. The mixture was

Stability of TiO<sup>2</sup> /poly(acrylic acid) (PAA) suspensions at different polymer content was measured on the basis of zeta potential measurements by means of the electrophoretic mobility. A zeta potential (ζ) of at least 30 mv (positive or negative) was normally required to achieve reasonably stable dispersion [13].

**Figure 15** presents the effect of the polymer content on the stability of the suspensions at initial pH (6). According to **Figure 10**, the addition of PAA resulted in a good dispersion of the

According to the executed studies, the addition of 3% PAA was considered as the ideal condition and the pH is adjusted at 6.The as-prepared suspension has a zeta potential about −37 mV. So, it is considered a well-stable suspension to carry on electrophoretic

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137

 *suspension as a function of sedimentation time*

nanoparticles into the pores of the anodic oxide using EPD

nanoparticles suspension. It should be noted that impregnation

sol because of the anodic electrolysis of water which decreases

**Figure 17** shows the absorbance of titanium dioxide suspensions with and without PAA as a function of sedimentation time. In these tests, the PAA concentration was fixed at 3% and the pH is adjusted at 6. It is observed that the absorbance of titanium dioxide suspensions is lowering as the sedimentation proceeds. It is noteworthy that the absorbance of the suspension in the presence of PAA is stable for at least a week. This means that the adsorbed PAA was expected to provide a degree of electrosteric stabilization. Based on these results, the suspension (3% PAA at pH = 6) was suggested as an optimal standpoint stability to per-

Electrophoretic impregnation of porous anodizing layer elaborated in phosphoric acid was

process is conditioned by the applied electric field. Applying high electric field (200 V/cm)

the pH near the electrode surface and then destabilize the suspension against coagulation at low pH. In order to avoid this phenomena and facilitate the insertion of titanium dioxide nanoparticles, the addition of the glycine to buffer the suspension is necessary. At the beginning of EPD, particles go to the bottom of pores which continue to fill progressively. These

suspensions as a function of time.

process [14].

process.

*2.3.4.1.4. Stability of the TiO2*

form the incorporation of TiO2

executed in aqueous TiO<sup>2</sup>

induce the jellification of TiO<sup>2</sup>

**Figure 17.** Variation of transmittance of the TiO<sup>2</sup>

*2.3.4.1.5. Electrophoretic impregnation of anodic coating*

**Figure 15.** Effect of the amount of PAA on the stability of TiO<sup>2</sup> suspension.

suspensions with negative charge. The increase of negatively charged ▬COO▬ groups was assignable to the modification of the TiO<sup>2</sup> nanoparticles surface charge. The addition of 3% PAA was considered as the ideal condition to study and discuss the stability under various pH regions.

#### *2.3.4.1.3. Effect of pH on the zeta potential of the TiO<sup>2</sup> suspension*

**Figure 16** shows the effect of pH on the zeta potential of the TiO<sup>2</sup> /3% PAA suspension. As the pH increased, the number of negatively charged sites is continually increased until the zeta potential reaches a value over −35 mV at pH ranging between 6 and 8.

**Figure 16.** Variation of zeta potential as a function of pH of the TiO<sup>2</sup> suspension with 3% PAA.

According to the executed studies, the addition of 3% PAA was considered as the ideal condition and the pH is adjusted at 6.The as-prepared suspension has a zeta potential about −37 mV. So, it is considered a well-stable suspension to carry on electrophoretic process [14].

#### *2.3.4.1.4. Stability of the TiO2 suspension as a function of sedimentation time*

**Figure 17** shows the absorbance of titanium dioxide suspensions with and without PAA as a function of sedimentation time. In these tests, the PAA concentration was fixed at 3% and the pH is adjusted at 6. It is observed that the absorbance of titanium dioxide suspensions is lowering as the sedimentation proceeds. It is noteworthy that the absorbance of the suspension in the presence of PAA is stable for at least a week. This means that the adsorbed PAA was expected to provide a degree of electrosteric stabilization. Based on these results, the suspension (3% PAA at pH = 6) was suggested as an optimal standpoint stability to perform the incorporation of TiO2 nanoparticles into the pores of the anodic oxide using EPD process.

#### *2.3.4.1.5. Electrophoretic impregnation of anodic coating*

suspensions with negative charge. The increase of negatively charged ▬COO▬ groups was

PAA was considered as the ideal condition to study and discuss the stability under various

pH increased, the number of negatively charged sites is continually increased until the zeta

 *suspension*

suspension.

nanoparticles surface charge. The addition of 3%

suspension with 3% PAA.

/3% PAA suspension. As the

assignable to the modification of the TiO<sup>2</sup>

136 Electrophoresis - Life Sciences Practical Applications

**Figure 15.** Effect of the amount of PAA on the stability of TiO<sup>2</sup>

*2.3.4.1.3. Effect of pH on the zeta potential of the TiO<sup>2</sup>*

**Figure 16.** Variation of zeta potential as a function of pH of the TiO<sup>2</sup>

**Figure 16** shows the effect of pH on the zeta potential of the TiO<sup>2</sup>

potential reaches a value over −35 mV at pH ranging between 6 and 8.

pH regions.

Electrophoretic impregnation of porous anodizing layer elaborated in phosphoric acid was executed in aqueous TiO<sup>2</sup> nanoparticles suspension. It should be noted that impregnation process is conditioned by the applied electric field. Applying high electric field (200 V/cm) induce the jellification of TiO<sup>2</sup> sol because of the anodic electrolysis of water which decreases the pH near the electrode surface and then destabilize the suspension against coagulation at low pH. In order to avoid this phenomena and facilitate the insertion of titanium dioxide nanoparticles, the addition of the glycine to buffer the suspension is necessary. At the beginning of EPD, particles go to the bottom of pores which continue to fill progressively. These

**Figure 17.** Variation of transmittance of the TiO<sup>2</sup> suspensions as a function of time.

barrier layer at the metal-porous anodic film interface [15]. This finding is in satisfactory agreement with that of Fori et al. [15]. The following equation describes the migration speed

Improving Tribological Behavior of Porous Anodic Film by Electrophoretic Impregnation by…

ν = μE (1)

where ν as the speed of nanoparticles (m/s), μ as the electrophoretic mobility of nanoparticles

**O3**

O3 /TiO<sup>2</sup>

**/TiO2**

Tribological tests were carried out on a non-anodized aluminum substrate, an anodized coat-

on the quantification of friction coefficient and the wear volume are shown in **Figures 20** and **21**,

Examination of **Figure 20** reveals that the friction coefficient of the anodic coating alone has two periods: (1) a period of 250 seconds (approximately 414 cycles) during which the average friction coefficient fluctuates at about 0.8 and (2) a second period marked by a sharp drop in the friction coefficient until reaching a stable value almost equal to that of the non-anodized

**Figure 20.** Variation of friction coefficient as a function of time (normal load Fn = 1 N, movement speed v = 0.052 m.s−1,

and a TiO2

nanopowder already synthesized by a sol-gel process, in order to study the

/s.V), and E as the electric field (V/m). According to the this equation, an increase of the electric field promotes the driving forces of particles and then facilitates their incorporation

 **composite coating**

nanoparticles. The results thus obtained bearing essentially

massive produced by compression of

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139

of the nanoparticles:

inside pores of the anodizing layer.

**3. Tribological behavior of Al2**

ing alone, a composite coating of Al<sup>2</sup>

effect of the incorporation of TiO<sup>2</sup>

a mass of a TiO2

and time of friction t = 15 min).

respectively.

(m<sup>2</sup>

results attest that EPD can be used to fill successfully porous-anodizing layer despite the presence of the resistive barrier layer at the metal-oxide interface. **Figure 18** reveals experimental setup of electrophoretic impregnation of anodizing layer by a synthesized TiO<sup>2</sup> nanoparticle and the filled anodic layer is shown in **Figure 19**.

As shown in **Figure 19**, an increase of the electric field improves the impregnation depth of nanoparticles. Hence high electric field is necessary here to compensate the resistive

**Figure 19.** FEG-SEM cross sectional views of the porous anodic oxide: (a) after electrophoresis process using 25 V/cm, (b) after electrophoresis process using 50 V/cm, and (c) after electrophoresis process using 200 V/cm.

barrier layer at the metal-porous anodic film interface [15]. This finding is in satisfactory agreement with that of Fori et al. [15]. The following equation describes the migration speed of the nanoparticles:

$$\mathbf{v} = \mu \mathbf{E} \tag{1}$$

where ν as the speed of nanoparticles (m/s), μ as the electrophoretic mobility of nanoparticles (m<sup>2</sup> /s.V), and E as the electric field (V/m). According to the this equation, an increase of the electric field promotes the driving forces of particles and then facilitates their incorporation inside pores of the anodizing layer.

#### **3. Tribological behavior of Al2 O3 /TiO2 composite coating**

results attest that EPD can be used to fill successfully porous-anodizing layer despite the presence of the resistive barrier layer at the metal-oxide interface. **Figure 18** reveals experimental

As shown in **Figure 19**, an increase of the electric field improves the impregnation depth of nanoparticles. Hence high electric field is necessary here to compensate the resistive

**Figure 19.** FEG-SEM cross sectional views of the porous anodic oxide: (a) after electrophoresis process using 25 V/cm, (b)

after electrophoresis process using 50 V/cm, and (c) after electrophoresis process using 200 V/cm.

nanoparticle

nanoparticle.

setup of electrophoretic impregnation of anodizing layer by a synthesized TiO<sup>2</sup>

**Figure 18.** Experimental setup of electrophoretic impregnation of anodizing layer by a synthesized TiO<sup>2</sup>

and the filled anodic layer is shown in **Figure 19**.

138 Electrophoresis - Life Sciences Practical Applications

Tribological tests were carried out on a non-anodized aluminum substrate, an anodized coating alone, a composite coating of Al<sup>2</sup> O3 /TiO<sup>2</sup> and a TiO2 massive produced by compression of a mass of a TiO2 nanopowder already synthesized by a sol-gel process, in order to study the effect of the incorporation of TiO<sup>2</sup> nanoparticles. The results thus obtained bearing essentially on the quantification of friction coefficient and the wear volume are shown in **Figures 20** and **21**, respectively.

Examination of **Figure 20** reveals that the friction coefficient of the anodic coating alone has two periods: (1) a period of 250 seconds (approximately 414 cycles) during which the average friction coefficient fluctuates at about 0.8 and (2) a second period marked by a sharp drop in the friction coefficient until reaching a stable value almost equal to that of the non-anodized

**Figure 20.** Variation of friction coefficient as a function of time (normal load Fn = 1 N, movement speed v = 0.052 m.s−1, and time of friction t = 15 min).

**Figure 21.** Optical micrographs of (a) the trace and (b) the alumina ball after friction test on (1) non-anodized aluminum, (2) anodic coating alone, and (3) composite coating Al<sup>2</sup> O3 /TiO<sup>2</sup> (Fn = 1 N, v = 0,052 ms− 1 and t = 15 min).

substrate (μ = 0.30) without causing a sudden variation. This reflects that this coating still persists in wear and has a lifetime greater than 900 seconds (1490 cycles). The optical image shown in **Figure 22 (3a)** shows that the composite coating has low wear free of microcracks. While, the

The characteristics of the wear traces of the various samples thus examined are measured and the volume of wear is calculated (**Figure 23**). The expertise of the latter figure shows that the

**Figure 23.** Variation of the wear volume of the worn samples after friction tests (Fn = 1 N, v = 0.052 m.s−1 and t = 15 min).

) and that of the anodic coating alone (373,106 μm<sup>3</sup>

tion (μ = 0.1) and a low wear volume justify a credible choice of TiO<sup>2</sup>

or oxide.

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) intermediate between that of the substrate

solid and (b) trace of wear of the counterface (alumina ball)

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141

). Such a coefficient of fric-

nanoparticles to be used

counterface (**Figure 21 (3b)**) does not show either TiO<sup>2</sup>

**Figure 22.** Optical micrographs (a) trace of wear of a TiO<sup>2</sup>

after friction test (Fn = 1 N, v = 0.052 m.s−1 and t = 15 min).

massive has a low wear volume (29.6106 μm<sup>3</sup>

TiO2

(461.4106 μm<sup>3</sup>

substrate (μ = 0.3). This particular drop of the coefficient of friction indicates the total damage of the anodic coating alone and the alumina ball, constitutes our counterface, then becomes in direct contact with the exposed aluminum. This is confirmed by the optical micrographs of the traces of wear of the ball and the anodic coating alone (**Figure 21**). The anodic coating is totally worn out after 250 seconds (414 cycles) and its trace revealing the substrate and metal debris on the ball.

The TiO2 massif has a friction coefficient (μ = 0.1) that is practically low throughout the tribological test compared to that of the substrate (μ = 0.30). Optical micrographs of the alumina ball show that TiO2 arbed on their surfaces (**Figure 21 (2b)** and **Figure 16 (b)**).

At this level, we can partially conclude that after measuring the friction coefficient of the aluminum alloy (μ = 0.3), the anodic coating alone and the TiO<sup>2</sup> massif (μ = 0.1), it was therefore possible to evaluate the coefficient of friction and the lifetime of the anodic coating alone (μ = 0.8 and a lifetime = 414 cycles).

The curve reflecting the variation of the coefficient of friction of the composite anodic coating Al<sup>2</sup> O3 /TiO<sup>2</sup> as a function of time evolves in two periods: (1) a first period (at approximately 100 seconds) during which the coefficient of friction is almost equal to that of the solid mass TiO2 (μ = 0.1) and (2) a second period (the rest of the friction test) during which the coefficient of friction increases slightly until reaching an almost stable value (μ = 0.15). These two periods respectively correspond to the ball contacts of alumina/TiO<sup>2</sup> deposited on the surface of the anodic coating and ball of alumina/composite coating.

It should be noted that the composite anodic coating will end up with a mean friction coefficient μ = 0.15, intermediate between that of the TiO<sup>2</sup> massive (μ = 0.1) and that of the non-anodized Improving Tribological Behavior of Porous Anodic Film by Electrophoretic Impregnation by… http://dx.doi.org/10.5772/intechopen.75782 141

**Figure 22.** Optical micrographs (a) trace of wear of a TiO<sup>2</sup> solid and (b) trace of wear of the counterface (alumina ball) after friction test (Fn = 1 N, v = 0.052 m.s−1 and t = 15 min).

substrate (μ = 0.30) without causing a sudden variation. This reflects that this coating still persists in wear and has a lifetime greater than 900 seconds (1490 cycles). The optical image shown in **Figure 22 (3a)** shows that the composite coating has low wear free of microcracks. While, the counterface (**Figure 21 (3b)**) does not show either TiO<sup>2</sup> or oxide.

The characteristics of the wear traces of the various samples thus examined are measured and the volume of wear is calculated (**Figure 23**). The expertise of the latter figure shows that the TiO2 massive has a low wear volume (29.6106 μm<sup>3</sup> ) intermediate between that of the substrate (461.4106 μm<sup>3</sup> ) and that of the anodic coating alone (373,106 μm<sup>3</sup> ). Such a coefficient of friction (μ = 0.1) and a low wear volume justify a credible choice of TiO<sup>2</sup> nanoparticles to be used

substrate (μ = 0.3). This particular drop of the coefficient of friction indicates the total damage of the anodic coating alone and the alumina ball, constitutes our counterface, then becomes in direct contact with the exposed aluminum. This is confirmed by the optical micrographs of the traces of wear of the ball and the anodic coating alone (**Figure 21**). The anodic coating is totally worn out after 250 seconds (414 cycles) and its trace revealing the substrate and metal

**Figure 21.** Optical micrographs of (a) the trace and (b) the alumina ball after friction test on (1) non-anodized aluminum,

(Fn = 1 N, v = 0,052 ms−

O3 /TiO<sup>2</sup>

logical test compared to that of the substrate (μ = 0.30). Optical micrographs of the alumina

At this level, we can partially conclude that after measuring the friction coefficient of the alu-

possible to evaluate the coefficient of friction and the lifetime of the anodic coating alone

The curve reflecting the variation of the coefficient of friction of the composite anodic coating

100 seconds) during which the coefficient of friction is almost equal to that of the solid mass

It should be noted that the composite anodic coating will end up with a mean friction coefficient

 (μ = 0.1) and (2) a second period (the rest of the friction test) during which the coefficient of friction increases slightly until reaching an almost stable value (μ = 0.15). These two periods

as a function of time evolves in two periods: (1) a first period (at approximately

minum alloy (μ = 0.3), the anodic coating alone and the TiO<sup>2</sup>

respectively correspond to the ball contacts of alumina/TiO<sup>2</sup>

anodic coating and ball of alumina/composite coating.

μ = 0.15, intermediate between that of the TiO<sup>2</sup>

arbed on their surfaces (**Figure 21 (2b)** and **Figure 16 (b)**).

massif has a friction coefficient (μ = 0.1) that is practically low throughout the tribo-

massif (μ = 0.1), it was therefore

1 and t = 15 min).

deposited on the surface of the

massive (μ = 0.1) and that of the non-anodized

debris on the ball.

ball show that TiO2

(μ = 0.8 and a lifetime = 414 cycles).

(2) anodic coating alone, and (3) composite coating Al<sup>2</sup>

140 Electrophoresis - Life Sciences Practical Applications

The TiO2

Al<sup>2</sup> O3 /TiO<sup>2</sup>

TiO2

**Figure 23.** Variation of the wear volume of the worn samples after friction tests (Fn = 1 N, v = 0.052 m.s−1 and t = 15 min).

for the electrophoretic impregnation of the anodic coating developed in a phosphoric bath in order to reinforce its tribological behavior.

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layer by synthesized TiO2

1.2404316735-739

(OCoLC)904102259

MRK654-01

Instrum: Malvern; 2017

colsurfa.2012.09.011

ceramint.2009.07.012

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Improving Tribological Behavior of Porous Anodic Film by Electrophoretic Impregnation by…

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143

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The composite anodic coating, as shown in **Figure 23**, has a wear volume (3.4106 μm<sup>3</sup> ) which has 0.73% of that of the substrate and about 0.91% of that of the anodic coating alone.

Finally, this panoply of the results confirms that the functionalization of the anodic coating by TiO2 nanoparticles contributes to a significant improvement in its resistance to frictional wear.

These results are in satisfactory agreement with those found by Yugeswaram et al. [16] in the case of an Al<sup>2</sup> O3 /13% TiO<sup>2</sup> composite coating developed by the Air Plasma Spray (APS) process.
