**2. Ferrite ceramics for CIM**

Ferrites are ceramic materials based on iron-oxide. They exhibit soft magnetism and therefore are being used in a variety of applications such as antennae, transformer cores, microwave waveguides, etc. There are three main types of ferrites: Mn-Zn ferrite, Ni-Zn ferrite and Mg-Zn ferrite. Ferrites have several advantages when compared to other materials: temperature and stability, high resistivity, wide frequency range and low loss combined with high permeability. Disadvantages are low saturation flux density and low tensile strength. Differences between soft ferrites and other magnetic materials are presented in Table 1 (Z. Stanimirović & I. Stanimirović, 2010).

There are several techniques available to forming ferrite specimens: grinding, extrusion, pressing and injection molding. Most ferrites are commercially produced by a dry pressing process. The powder flows into a die cavity and upper and lower punches at about 10 tons per surface square inch are being applied. Since the pressing is being done in vertical direction, resulting specimen geometries are limited to simple geometric shapes. Grinding is the most economical forming technique to produce non standard ferrite cores. It requires no tooling since cores are ground from isostatically formed sintered bars. Extrusion is an ideal technique for forming long rods and bars.


Table 1. Differences between soft ferrites and other magnetic materials.

However, in recent years ceramic injection molding technique (Rodrigez et al., 2003; Zlatkov et al., 2008) has been applied as an alternative forming process. Injection molded ferrite parts can be produced from very simple forms to quite complex shapes. Further processing is rarely required, but if necessary, this can be achieved using conventional tools. Parts produced through this process can have very intricate shapes and tight tolerances. Injection

Ceramic Injection Molding 135

Fig. 4. Disc shaped CIM Mn-Zn ferrite samples (diameter d=16mm, thickness t=5mm).

Fig. 5. Ring shaped CIM Mn-Zn ferrite samples (outer diameter do=15mm, inner diameter

1320/2 5.83 89.2 1518 1305 13.21 13.9 1320/2 4.80 - 1238 1360 17.43 11.71 1320/4 7.71 - 1463 1463 23.52 21.60 1280/2 4.20 87.1 922.5 922.5 24.15 23.33 1250/4 4.50 90.4 717.7 - 37.18 - 1320/2 4.33 90.1 1609 1456 9.0 9.18 1320/2 n.a. 85.1 733.4 716.3 50.94 42.06 Table 3. The main properties of injection molded sintered ring shaped Mn-Zn ferrite specimens.

Initial relative permeability 750±25% 900±25% Operating frequency range [MHz] 0.1-1 0,01-0,5

Magnetic Induction [mT] 390 390 Table 4. Comparative properties of injection molded sintered Mn-Zn ferrite ring and disc

Relative loss factor 810-6-3010-6 510-6-2510-6

Experimental work demonstrated that Mn-Zn ferrite ceramics can be prepared using injection molding technique but the process is not trivial. For example, a special attention must be paid to initial filling of the mold. Due to uneven shrinkage rate during

[% TD] Initial relative permeability Loss factor

Ring shaped specimens Disc shaped specimens

[10-6]

Relative density

di=6mm, thickness t=5mm).

Grain size [μm]

Tsint/t [°C/h]

shaped specimens.

molded ferrite components have properties similar to conventionally produced parts (Skolyszewska et al., 2003; Zlatkov et al., 2010).

Manganese zinc ferrite is a magnetically soft material suitable for use as magnetic cores in low frequency range (1kHz-1MHz). For soft ferrite magnetic core production uniaxial powder pressing technique is usually used. However, CIM as an extremely flexible technology enabled production of Mn-Zn ferrites with characteristics comparable with commercial samples prepared by conventional methods. There are two reasons for CIM investigations of Mn-Zn ferrites: the shape complexity and the better permeability.

The starting material used for the production of Mn-Zn ferrite samples was commercially available Mn-Zn ferrite powder shown in Fig. 3(a). Prior to injection molding, powder was processed in a conventional manner. Mn-Zn ferrite powder in combination with binder (combination of polypropylene, microcrystalline wax and stearic acid) was used for feedstock production. Feedstock contained 10.5% of binder (9% wax, 1% wax with lower melting temperature, 1% of stabilizer) and 68% of Mn-Zn ceramic ferrite powder. Photograph of Mn-Zn ferrite feedstock is shown in Fig. 3(b).

Fig. 3. Mn-Zn ferrite: powder (a) and feedstock (b).

Injection molding was performed using molds in shapes required to form ring and disc shaped specimens. The injection molding process was carried out in Battenfeld HM 250/60- B4 machine and main injection molding parametres are given in Table 2. Debinding of green parts after injection molding was performed in two steps: solvent and thermal debinding. Thermal debinding was performed during initial priod of sintering (150-800ºC heating period) and the green ferrite samples were sintered at 1280-1320ºC/1-4h in nitrogen atmosphere.


Table 2. Main injection molding parameters.

Photographs and dimensions of injection molded ring and disc shaped CIM Mn-Zn specimens are given in Fig. 4 and Fig. 5. The main properties of injection molded sintered Mn-Zn ferrite ring shaped specimens are given in Table 3 and the comparative properties of injection molded sintered Mn- Zn ferrite ring and disc shaped specimens are given in Table 4.

molded ferrite components have properties similar to conventionally produced parts

Manganese zinc ferrite is a magnetically soft material suitable for use as magnetic cores in low frequency range (1kHz-1MHz). For soft ferrite magnetic core production uniaxial powder pressing technique is usually used. However, CIM as an extremely flexible technology enabled production of Mn-Zn ferrites with characteristics comparable with commercial samples prepared by conventional methods. There are two reasons for CIM

The starting material used for the production of Mn-Zn ferrite samples was commercially available Mn-Zn ferrite powder shown in Fig. 3(a). Prior to injection molding, powder was processed in a conventional manner. Mn-Zn ferrite powder in combination with binder (combination of polypropylene, microcrystalline wax and stearic acid) was used for feedstock production. Feedstock contained 10.5% of binder (9% wax, 1% wax with lower melting temperature, 1% of stabilizer) and 68% of Mn-Zn ceramic ferrite powder.

(a) (b)

Injection molding was performed using molds in shapes required to form ring and disc shaped specimens. The injection molding process was carried out in Battenfeld HM 250/60- B4 machine and main injection molding parametres are given in Table 2. Debinding of green parts after injection molding was performed in two steps: solvent and thermal debinding. Thermal debinding was performed during initial priod of sintering (150-800ºC heating period) and the green ferrite samples were sintered at 1280-1320ºC/1-4h in nitrogen

> **Parameter Setup**  Injection temperature (ºC) 120-160 Mold temperature (ºC) 30-45 Injection speed (ccm/s) 3-20 Injection pressure (bar) 300-800 Cooling time (s) 10 Sample ejection pressure (bar) 20-40

Photographs and dimensions of injection molded ring and disc shaped CIM Mn-Zn specimens are given in Fig. 4 and Fig. 5. The main properties of injection molded sintered Mn-Zn ferrite ring shaped specimens are given in Table 3 and the comparative properties of injection

molded sintered Mn- Zn ferrite ring and disc shaped specimens are given in Table 4.

investigations of Mn-Zn ferrites: the shape complexity and the better permeability.

(Skolyszewska et al., 2003; Zlatkov et al., 2010).

Photograph of Mn-Zn ferrite feedstock is shown in Fig. 3(b).

Fig. 3. Mn-Zn ferrite: powder (a) and feedstock (b).

Table 2. Main injection molding parameters.

atmosphere.

Fig. 4. Disc shaped CIM Mn-Zn ferrite samples (diameter d=16mm, thickness t=5mm).

Fig. 5. Ring shaped CIM Mn-Zn ferrite samples (outer diameter do=15mm, inner diameter di=6mm, thickness t=5mm).


Table 3. The main properties of injection molded sintered ring shaped Mn-Zn ferrite specimens.


Table 4. Comparative properties of injection molded sintered Mn-Zn ferrite ring and disc shaped specimens.

Experimental work demonstrated that Mn-Zn ferrite ceramics can be prepared using injection molding technique but the process is not trivial. For example, a special attention must be paid to initial filling of the mold. Due to uneven shrinkage rate during

Ceramic Injection Molding 137

barium titanate (BaTiO3) are ceramic materials that have found widespread use – especially lead zirconate titanate that is being widely used in sensors, transducers, microactuators, multilayer capacitors and micro-electromechanical systems (MEMS). These materials are known for their superior piezoelectric and ferroelectric properties. When a mechanical force is applied, piezoelectric materials generate electrical voltage. Conversely, when an electric field is applied, these materials induce mechanical stress or strains. These effects are known

Conventional powder metallurgy method is a commonly used method to produce piezoelectric materials. It starts with powder preparation. The powder is pressed to required shapes and size, and green shapes are processed into mechanically strong and dense ceramics. Machining process is being used for achieving desired shapes of the components. Elecroding and poling are the final sterps of the process. When complex shapes are in question, cutting and machining of piezoelectric ceramics are time consuming. There are

The most of the published papers have dealt with fabrication and electrical properties of piezoelectric ceramics produced using conventional powder metallurgy method (Fig. 7). However, a little work has been carried out on the fabrication and characterisation of piezoelectric ceramics prepared by ceramic powder injection molding method (CIM) (Luo et al., 2006; Wang et al., 1999, Zlatkov et al., 2008). In order to synthesise piezoelectric ceramics

Fig. 7. Piezoelectric ceramics production: conventional powder metallurgy method vs. CIM

method (I. Stanimirović & Z. Stanimirović, 2010).

as direct piezoelectric effect and converse piezoelectric effect, respectively.

also cost considerations because of the cost of the die and the waste material.

solidification, creation of stresses within the body of the sample may occur resulting in nucleation of voids or cracks. Also, if air pockets remain within the body of the specimen this may lead to poor properties of the realized component.

Problems may also occur during the burn out of the binder. Burn-out can be performed in air but this may cause excessive specimen shrinkage and surface layer exfoliation due to oxidative reaction. For that reason, nitrogen atmosphere was used. Sintering and densification of the specimen during sintering is a key factor that determines magnetic properties of the sample. Highest temperature used (1320 ºC) yielded the highest sample densities and as illustration SEM microstructure of CIM Mn-Zn ring shaped ferrite specimen sintered at 1320ºC/2h is shown in Fig. 6.

Fig. 6. SEM microstructure of CIM Mn-Zn ring shaped ferrite specimen sintered at 1320ºC/2h.

The grain sizes of injection molded specimens are usually smaller than grain sizes of conventionally produced Mn-Zn ferrites. Injection molding process leads to similar specimen densities when compared to conventional methods but grain sizes are up to 50% smaller. Increase of the sintering time from 2h to 4h results in grain growth normally expected for Mn-Zn samples. Smaller grain sizes lead to more grain boundaries and therefore more pinning centers resulting in lower permeability. Grain growth during prolonged sintering cycle leads to greater densities and increased permeability but at temperatures higher than 1180ºC (Pigram & Freer, 1994) zinc volatilization occurs leading to zinc loss. For that reason, temperature of 1150ºC (Pigram & Freer, 1994) is recommended for adequate grain growth without zinc volatilization. Therefore, further work to optimize the processing conditions is desirable. The goal is to increase the grain size and initial permeability of realized specimens.

Experimental work on Mn-Zn ferrite has shown that ferrite ceramics can be prepared using injection molding technique although the process is not trivial and optimization of both tools and processing conditions is essential. Mn-Zn sintering obtained by CIM technology is sensitive process compared to the conventional pressing technology, but the obtained results are satisfactory. Realized Mn-Zn ferrite specimens have high green-state strength, ideal for production of delicate and complex shapes. Also, specimens exhibit satisfactory structural integrity and magnetic properties, as well as densities similar to conventionally produced material.

#### **3. Piezoelectric ceramics for CIM**

Piezoelectric ceramics is one of the functional materials which have unique electrical properties with broadening range of applications. Lead zirconate titanate (PbZrTiO3) and

solidification, creation of stresses within the body of the sample may occur resulting in nucleation of voids or cracks. Also, if air pockets remain within the body of the specimen

Problems may also occur during the burn out of the binder. Burn-out can be performed in air but this may cause excessive specimen shrinkage and surface layer exfoliation due to oxidative reaction. For that reason, nitrogen atmosphere was used. Sintering and densification of the specimen during sintering is a key factor that determines magnetic properties of the sample. Highest temperature used (1320 ºC) yielded the highest sample densities and as illustration SEM microstructure of CIM Mn-Zn ring shaped ferrite specimen

Fig. 6. SEM microstructure of CIM Mn-Zn ring shaped ferrite specimen sintered at 1320ºC/2h.

The grain sizes of injection molded specimens are usually smaller than grain sizes of conventionally produced Mn-Zn ferrites. Injection molding process leads to similar specimen densities when compared to conventional methods but grain sizes are up to 50% smaller. Increase of the sintering time from 2h to 4h results in grain growth normally expected for Mn-Zn samples. Smaller grain sizes lead to more grain boundaries and therefore more pinning centers resulting in lower permeability. Grain growth during prolonged sintering cycle leads to greater densities and increased permeability but at temperatures higher than 1180ºC (Pigram & Freer, 1994) zinc volatilization occurs leading to zinc loss. For that reason, temperature of 1150ºC (Pigram & Freer, 1994) is recommended for adequate grain growth without zinc volatilization. Therefore, further work to optimize the processing conditions is desirable. The goal is to increase the grain size and initial

Experimental work on Mn-Zn ferrite has shown that ferrite ceramics can be prepared using injection molding technique although the process is not trivial and optimization of both tools and processing conditions is essential. Mn-Zn sintering obtained by CIM technology is sensitive process compared to the conventional pressing technology, but the obtained results are satisfactory. Realized Mn-Zn ferrite specimens have high green-state strength, ideal for production of delicate and complex shapes. Also, specimens exhibit satisfactory structural integrity and magnetic properties, as well as densities similar to conventionally

Piezoelectric ceramics is one of the functional materials which have unique electrical properties with broadening range of applications. Lead zirconate titanate (PbZrTiO3) and

this may lead to poor properties of the realized component.

sintered at 1320ºC/2h is shown in Fig. 6.

permeability of realized specimens.

**3. Piezoelectric ceramics for CIM** 

produced material.

barium titanate (BaTiO3) are ceramic materials that have found widespread use – especially lead zirconate titanate that is being widely used in sensors, transducers, microactuators, multilayer capacitors and micro-electromechanical systems (MEMS). These materials are known for their superior piezoelectric and ferroelectric properties. When a mechanical force is applied, piezoelectric materials generate electrical voltage. Conversely, when an electric field is applied, these materials induce mechanical stress or strains. These effects are known as direct piezoelectric effect and converse piezoelectric effect, respectively.

Conventional powder metallurgy method is a commonly used method to produce piezoelectric materials. It starts with powder preparation. The powder is pressed to required shapes and size, and green shapes are processed into mechanically strong and dense ceramics. Machining process is being used for achieving desired shapes of the components. Elecroding and poling are the final sterps of the process. When complex shapes are in question, cutting and machining of piezoelectric ceramics are time consuming. There are also cost considerations because of the cost of the die and the waste material.

The most of the published papers have dealt with fabrication and electrical properties of piezoelectric ceramics produced using conventional powder metallurgy method (Fig. 7). However, a little work has been carried out on the fabrication and characterisation of piezoelectric ceramics prepared by ceramic powder injection molding method (CIM) (Luo et al., 2006; Wang et al., 1999, Zlatkov et al., 2008). In order to synthesise piezoelectric ceramics

Fig. 7. Piezoelectric ceramics production: conventional powder metallurgy method vs. CIM method (I. Stanimirović & Z. Stanimirović, 2010).

Ceramic Injection Molding 139

The feedstock was then heated to a sufficient temperature - such that it melted and injected into a mold cavity where it cooled and formed desired shape. The injection molding process was carried out in Battenfeld HM 250/60-B4 machine and the main parameters of injection molding corresponded to ones listed in Table 2. Dimensions of green bodies were 20mm×10mm×2mm. In accordance with the binder system, debinding procedure was performed. A two-stage debinding technique was applied. The solvent debinding stage was followed by thermal debinding stage. The main debinding parameters are given in Table 6. The slow heating rate prevented defects such as micro-cracks, slumping and blistering of the

In a water bath: 24h in a destilled water

After the debinding process, the debinded parts were sintered in an air atmosphere. In order to minimize lead loss from PbZrTiO3 bodies that occur at about 800ºC, these samples were sintered in presence of a lead source. Basic information about the sintering process is given

> Butch kiln ELEKTRON 1500 Sagger Alumina 98% Sagger cover Alumina 98% Bottom plates ZrO2

safety powder ZrO2 and Pb3O4

Manual filling 20 psc. green bodies/sagger

Dimensions of sintered samples were 16.67mm×8.43mm×1.52mm (PbZrTiO3 samples) and 16.6mm×8.42mm×1.5mm (BaTiO3 samples). After the sintering process, PbZrTiO3 samples

Air atmosphere 21ºC -600ºC, rising degree [100ºC/h] PbZrTiO3: 600ºC-1250ºC, BaTiO3: 600ºC-1260ºC, rising degree [150ºC/h] PbZrTiO3: 1250 ºC, BaTiO3: 1260 ºC, holding time 2h Cooling 1250ºC /1260ºC–21ºC: Natural

4h at 80ºC 80ºC - 145ºC, rising degree [20ºC/h] 145ºC - 155ºC, rising degree [0.5ºC/h] 155ºC - 160ºC, rising degree [0.2ºC/h] At 160 ºC holding time 4h 160ºC - 170ºC, rising degree [2-5ºC/h] 170ºC - 220ºC, rising degree [10ºC/h] 220ºC - 300ºC, rising degree [20ºC/h] At 300 ºC holding time 2h

parts to be induced during debinding process.

In chamber drying device with fan:

Setting and

Sintering conditions

Table 7. Sintering process.

Table 6. Two-stage debinding procedure.

in Table 7.

using CIM process, four basic steps should be performed: feedstock preparation, ceramic injection molding, debinding and sintering. Components produced by CIM are expected to have more complex shapes and more homogeneous microstructure than components produced by conventional metallurgy method. Also, reduced machining and recycling use of feedstock are significantly reducing fabrication costs.

In order to explore the feasibility to synthesise piezoelectric ceramics by CIM, two series of test samples were realized (I. Stanimirović & Z. Stanimirović, 2010). Commercially available BaTiO3 and PbZrTiO3 powders were used. Basic properties of used powders are given in Table 5. Also, photographs of BaTiO3 and PbZrTiO3 powders are given in Fig. 8, as well as the micrograph of PbZrTiO3 powder particles Fig. 9(a).


Table 5. Basic properties of BaTiO3 and PbZrTiO3 powders.

Fig. 9. Scanning electron micrograph of PbZrTiO3 powder particles (a) and PbZrTiO3 feedstock (b).

These starting materials in combination with binder were used for feedstock production. Each feedstock contained 10.5% of binder (9% wax, 1% wax with lower melting temperature, 1% of stabilizer). Photograph of PbZrTiO3 feedstock is shown in Fig. 9(b).

using CIM process, four basic steps should be performed: feedstock preparation, ceramic injection molding, debinding and sintering. Components produced by CIM are expected to have more complex shapes and more homogeneous microstructure than components produced by conventional metallurgy method. Also, reduced machining and recycling use

In order to explore the feasibility to synthesise piezoelectric ceramics by CIM, two series of test samples were realized (I. Stanimirović & Z. Stanimirović, 2010). Commercially available BaTiO3 and PbZrTiO3 powders were used. Basic properties of used powders are given in Table 5. Also, photographs of BaTiO3 and PbZrTiO3 powders are given in Fig. 8, as well as

> Ceramic powder: BaTiO3 PbZrTiO3 Density [g/cm3] 6,2 7,8 Dielectric constant 33/<sup>0</sup> 1700 2200 Isolation resistance [m] 1011 1011

coefficient d33 [C/N] 12010-12 <sup>450</sup>10-12 Curie temperature TC [○С] 118 350 Specific surface area [m2/g] 2,6 2,7

(a) (b)

(a) (b)

These starting materials in combination with binder were used for feedstock production. Each feedstock contained 10.5% of binder (9% wax, 1% wax with lower melting temperature, 1% of stabilizer). Photograph of PbZrTiO3 feedstock is shown in Fig. 9(b).

Fig. 9. Scanning electron micrograph of PbZrTiO3 powder particles (a) and PbZrTiO3

0,50 0,69

Electromechanical coupling

of feedstock are significantly reducing fabrication costs.

the micrograph of PbZrTiO3 powder particles Fig. 9(a).

coefficient k33

Piezoelectric

Table 5. Basic properties of BaTiO3 and PbZrTiO3 powders.

Fig. 8. BaTiO3 powder (a) and PbZrTiO3 powder (b).

feedstock (b).

The feedstock was then heated to a sufficient temperature - such that it melted and injected into a mold cavity where it cooled and formed desired shape. The injection molding process was carried out in Battenfeld HM 250/60-B4 machine and the main parameters of injection molding corresponded to ones listed in Table 2. Dimensions of green bodies were 20mm×10mm×2mm. In accordance with the binder system, debinding procedure was performed. A two-stage debinding technique was applied. The solvent debinding stage was followed by thermal debinding stage. The main debinding parameters are given in Table 6. The slow heating rate prevented defects such as micro-cracks, slumping and blistering of the parts to be induced during debinding process.


Table 6. Two-stage debinding procedure.

After the debinding process, the debinded parts were sintered in an air atmosphere. In order to minimize lead loss from PbZrTiO3 bodies that occur at about 800ºC, these samples were sintered in presence of a lead source. Basic information about the sintering process is given in Table 7.


Table 7. Sintering process.

Dimensions of sintered samples were 16.67mm×8.43mm×1.52mm (PbZrTiO3 samples) and 16.6mm×8.42mm×1.5mm (BaTiO3 samples). After the sintering process, PbZrTiO3 samples

Ceramic Injection Molding 141

dielectric constants obtained by two methods can be attributed to microstructure development

Electromechanical coupling coefficient and piezoelectric coefficient are slightly lower than those from reference, while the loss tangent is higher for samples realized using CIM method than for samples obtained by conventional metallurgy method. They strongly depend on processing parameters, especially sintering temperatures, and by further adjustment of various processing parameters, CIM technology can provide PbZrTiO3 components with application-specific properties similar to those provided by conventionally

Obtained results have shown that piezoelectric ceramics can be successfully produced by CIM method. Sintering temperature was found to play important role in physical, mechanical and electrical properties since it affects sample density and porosity. The obtained sample properties were comparable to those found in literature. It is important to note that in comparison with conventional powder metallurgy, CIM samples have more homogenous microstructure and production costs are reduced by reducing machining and recycling use of feedstock. Further research should be focused on processing conditions and their influence on the properties of final sintered parts, assuring satisfactory low-cost alternative for the production of piezoelectric ceramics with application specific properties.

Aluminium oxide (Al2O3) is ceramics with high mechanical hardness, high electrical resistivity and thermal conductivity. It has good strength and stiffness, good wear and corrosion resistance, good thermal stability, low dielectric constant and loss tangent, low thermal expansion, low weight, etc. It is suitable for technical ceramic, electronic and medical products, etc. CIM alumina exhibits properties close to pressed and sintered samples (Hwang & Hsieh, 2005; Hausnerova et al., 2011; Krauss et al., 2005). The most common material that is being used for feedstock preparation is Al2O3 powder with 99.7% purity (Wei et al., 2000). Properties and scanning electron micrograph of 99.7% alumina

Multicomponent binder commonly used in feedstock preparation is 30wt% polypropilene, 65wt% paraffin wax and 5wt% stearic acid. After injection molding procedure, samples are being subjected to a debinding process (Table 11). After the debinding procedure, all

Dielectric constant 33/<sup>0</sup> 1700±30 1210 Loss tangent tgδmax 0.02 1.0

CIM method Conventional powder

0.50 0.27

120±50 97

metallurgy method (Gu et al., 2008)

and change in grain size with variation of sintering temperature.

Electromechanical coupling coefficient k33

Table 9. Comparative properties of PbZrTiO3 samples.

Piezoelectric coefficient d33 [10-12C/N]

produced components.

**4. Alumina for CIM** 

powder are given in Table 10 and Fig. 12.

were silver plated using screen printing process and fired in an air atmosphere at 750ºC/10min. All samples were then polarized and functional and electrical measurements were performed (Table 8). Photographs of CIM PbZrTiO3 and BaTiO3 samples are given in Fig. 10 and Fig. 11.

Fig. 10. CIM PbZrTiO3 samples: green (a) and sintered and silver plated (b).

Fig. 11. CIM BaTiO3 samples.


Table 8. Basic properties of BaTiO3 and PbZrTiO3 samples.

In order to evaluate feasibility of producing piezoelectric ceramics by conventional metallurgy method and CIM, we compared results for CIM PbZrTiO3 samples obtained from our study (Table 9) with those found in literature (Gu et al., 2008). Table 9 lists dielectric constants, loss tangents, electromechanical coupling coefficients and piezoelectric coefficients for samples obtained by those two methods.

The dielectric constant is a measure of charge stored on an electrode material brought to a given voltage. It strongly depends on sintering temperature for both CIM and conventional metallurgy method. When conventional method is concerned, dielectric constant increases with sintering temperature due to the increase in PbZrTiO3 grains. For CIM samples, dielectric constant increases with sintering temperature to 1250ºC and then decreases with sintering temperature because of the deceased density due to lead loss. Therefore observed difference in

were silver plated using screen printing process and fired in an air atmosphere at 750ºC/10min. All samples were then polarized and functional and electrical measurements were performed (Table 8). Photographs of CIM PbZrTiO3 and BaTiO3 samples are given in

(a) (b)

 BaTiO3 PbZrTiO3 Dielectric constant 33/<sup>0</sup> 2000±30 1700±30 Loss tangent tgδmax 0.02 0.02

In order to evaluate feasibility of producing piezoelectric ceramics by conventional metallurgy method and CIM, we compared results for CIM PbZrTiO3 samples obtained from our study (Table 9) with those found in literature (Gu et al., 2008). Table 9 lists dielectric constants, loss tangents, electromechanical coupling coefficients and piezoelectric

The dielectric constant is a measure of charge stored on an electrode material brought to a given voltage. It strongly depends on sintering temperature for both CIM and conventional metallurgy method. When conventional method is concerned, dielectric constant increases with sintering temperature due to the increase in PbZrTiO3 grains. For CIM samples, dielectric constant increases with sintering temperature to 1250ºC and then decreases with sintering temperature because of the deceased density due to lead loss. Therefore observed difference in

0.65 0.50

550±5010-12 120±5010-12

Fig. 10. CIM PbZrTiO3 samples: green (a) and sintered and silver plated (b).

Electromechanical coupling

coefficient k33

Piezoelectric

coefficient d33 [C/N]

Table 8. Basic properties of BaTiO3 and PbZrTiO3 samples.

coefficients for samples obtained by those two methods.

Fig. 10 and Fig. 11.

Fig. 11. CIM BaTiO3 samples.


dielectric constants obtained by two methods can be attributed to microstructure development and change in grain size with variation of sintering temperature.

Table 9. Comparative properties of PbZrTiO3 samples.

Electromechanical coupling coefficient and piezoelectric coefficient are slightly lower than those from reference, while the loss tangent is higher for samples realized using CIM method than for samples obtained by conventional metallurgy method. They strongly depend on processing parameters, especially sintering temperatures, and by further adjustment of various processing parameters, CIM technology can provide PbZrTiO3 components with application-specific properties similar to those provided by conventionally produced components.

Obtained results have shown that piezoelectric ceramics can be successfully produced by CIM method. Sintering temperature was found to play important role in physical, mechanical and electrical properties since it affects sample density and porosity. The obtained sample properties were comparable to those found in literature. It is important to note that in comparison with conventional powder metallurgy, CIM samples have more homogenous microstructure and production costs are reduced by reducing machining and recycling use of feedstock. Further research should be focused on processing conditions and their influence on the properties of final sintered parts, assuring satisfactory low-cost alternative for the production of piezoelectric ceramics with application specific properties.
