《复合材料 Composites》课程教学资源（学习资料）第五章 陶瓷基复合材料_electrophoretic deposition-11

CERAMICS INTERNATIONAL SEVIER Ceramics International 30(2004)843-852 www.elsevier.com/locate/ceramint Electrophoretic deposition of alumina and zirconia I Single-component systems Karel Maca", Hynek Hadraba, Jaroslav Cihlar Department of Ceramics, Brno University of Technolog 616 69 Brno, Czech Republic Received 30 May 2003: received in revised form 17 August 2003; accepted 25 September 2003 Available online 20 March 2004 Abstract Electrophoretic deposition of Al,, and ZrO, suspended in isopropanol in the presence of monochloroacetic acid and polyvinylbuty under constant-current conditions was studied. The deposition of ceramic particles occurred on the anode. An optimum deposition in terms of surface flatness, deposit density and thickness was found for 15 wt. of monochloroacetic acid in isopropanol. The electrophoretic mobility of alumina particles in this suspension was determined from deposition kinetics. The sintering behaviour, hardness, fracture toughness and ending strength of Al2O3 and ZrO2 electrophoretic deposits were comparable with the values measured for the specimens prepared from identical powders by injection moulding and cold isostatic pressing or with the values given in the literature C 2003 Elsevier Ltd and Techna Group S.r. l. All rights reserved Keywords: B Composites, D. Al2O3; D ZrO2; Electrophoretic deposition 1. Introduction time suspension stability is the limiting factor with respect to obtaining a deposit of high density [10] Electrophoretic deposition is an experimentally unde- Zhitomirski [ll] described electrophoretic manding and comparatively cheap technique enabling the 12O3 and ZrO2 powders in propanol without admixtures formation of deposits from particles of nanometric di- and at voltages from 50 to 200V, he deposited within mensions [1, 2] to particles of several micrometers in size 10-300 s a deposit of 1-10 um in thickness. By contrast, 3]. Electrophoretic deposition can yield layers of a wide Harbach and Nienburg [5,6] described a ZrO2 suspension range of thickness, from several nanometers [4] to several in pure isopropanol and ethanol as unstable. The authors millimetres [5, 6] obtained better results using ZrO2 dispersed in ethanol Usually, electrophoretic deposition of Al2O3 and ZrO2 and isopropanol stabilized with 4-hydroxy benzoic acid, in aqueous medium is described in the literature [7, 8]. The polyethylenimine and acrylate-acrylamid copolymer. The advantage of using aqueous suspensions for electrophoretic same authors deposited AlO3 tubes stabilized with trioxy- deposition lies in the easy preparation of stable suspensions decanoic acid in isopropanol. will et al. [ 12] stabilized Zroz of ceramic particles and the ease of controlling the charge powder for deposition in ethanol using polyethylenimine on particle surface by changing the ph value of aqueous Ishihara and coworkers [ 13, 14] tested a great number of sol- medium [9]. However, using aqueous solutions results in vents from the viewpoint of the surface quality of the Zro2 the electrolysis of water, with gaseous hydrogen generated deposit. They obtained the best results when using acety- on the cathode and oxygen on the anode. These gases form lactone, in which he stabilized the zrO2 particles by means bubbles in the deposit, reduce its density and prevent the of iodine. Chen and Liu [15] used iodine to stabilize Zroz deposit from adhering to the electrode[7]. On the other side particles in a mixture of one volume part of ethanol( which he disadvantage of using suspensions with organic solvents improved the resistance of the deposit to cracking during is that the particles are more difficult to stabilize; at the same drying) and three volume parts of acetone(which improved the surface quality of the deposit). Basu et al. [16] deposited dried ZrO2 from anhydrous medium of glacial acetic acid. Corresponding author. Fax: +420-541143202 Most of the references describe electrophoretic E-mail address: maca @umi. fme. vutbr cz(K. Maca) ition at a constant voltage [5,8,9, 11, 15, 17-19]. In this 0272-8842/$30.00 0 2003 Elsevier Ltd and Techna Group S r l. All rights reserved doi:10.1016/ ceramist2003.09.021

Ceramics International 30 (2004) 843–852 Electrophoretic deposition of alumina and zirconia I. Single-component systems Karel Maca∗, Hynek Hadraba, Jaroslav Cihlar Department of Ceramics, Brno University of Technology, 616 69 Brno, Czech Republic Received 30 May 2003; received in revised form 17 August 2003; accepted 25 September 2003 Available online 20 March 2004 Abstract Electrophoretic deposition of Al2O3 and ZrO2 suspended in isopropanol in the presence of monochloroacetic acid and polyvinylbutyral under constant-current conditions was studied. The deposition of ceramic particles occurred on the anode. An optimum deposition in terms of surface flatness, deposit density and thickness was found for 15 wt.% of monochloroacetic acid in isopropanol. The electrophoretic mobility of alumina particles in this suspension was determined from deposition kinetics. The sintering behaviour, hardness, fracture toughness and bending strength of Al2O3 and ZrO2 electrophoretic deposits were comparable with the values measured for the specimens prepared from identical powders by injection moulding and cold isostatic pressing or with the values given in the literature. © 2003 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: B. Composites; D. Al2O3; D. ZrO2; Electrophoretic deposition 1. Introduction Electrophoretic deposition is an experimentally unde￾manding and comparatively cheap technique enabling the formation of deposits from particles of nanometric di￾mensions [1,2] to particles of several micrometers in size [3]. Electrophoretic deposition can yield layers of a wide range of thickness, from several nanometers [4] to several millimetres [5,6]. Usually, electrophoretic deposition of Al2O3 and ZrO2 in aqueous medium is described in the literature [7,8]. The advantage of using aqueous suspensions for electrophoretic deposition lies in the easy preparation of stable suspensions of ceramic particles and the ease of controlling the charge on particle surface by changing the pH value of aqueous medium [9]. However, using aqueous solutions results in the electrolysis of water, with gaseous hydrogen generated on the cathode and oxygen on the anode. These gases form bubbles in the deposit, reduce its density and prevent the deposit from adhering to the electrode [7]. On the other side the disadvantage of using suspensions with organic solvents is that the particles are more difficult to stabilize; at the same ∗ Corresponding author. Fax: +420-541143202. E-mail address: maca@umi.fme.vutbr.cz (K. Maca). time suspension stability is the limiting factor with respect to obtaining a deposit of high density [10]. Zhitomirski [11] described electrophoretic deposition of Al2O3 and ZrO2 powders in propanol without admixtures, and at voltages from 50 to 200 V, he deposited within 10–300 s a deposit of 1–10
m in thickness. By contrast, Harbach and Nienburg [5,6] described a ZrO2 suspension in pure isopropanol and ethanol as unstable. The authors obtained better results using ZrO2 dispersed in ethanol and isopropanol stabilized with 4-hydroxybenzoic acid, polyethylenimine and acrylate-acrylamid copolymer. The same authors deposited Al2O3 tubes stabilized with trioxy￾decanoic acid in isopropanol. Will et al. [12] stabilized ZrO2 powder for deposition in ethanol using polyethylenimine. Ishihara and coworkers [13,14] tested a great number of sol￾vents from the viewpoint of the surface quality of the ZrO2 deposit. They obtained the best results when using acety￾lacetone, in which he stabilized the ZrO2 particles by means of iodine. Chen and Liu [15] used iodine to stabilize ZrO2 particles in a mixture of one volume part of ethanol (which improved the resistance of the deposit to cracking during drying) and three volume parts of acetone (which improved the surface quality of the deposit). Basu et al. [16] deposited dried ZrO2 from anhydrous medium of glacial acetic acid. Most of the references describe electrophoretic depo￾sition at a constant voltage [5,8,9,11,15,17–19]. In this 0272-8842/$30.00 © 2003 Elsevier Ltd and Techna Group S.r.l. All rights reserved. doi:10.1016/j.ceramint.2003.09.021

844 K. Maca et al. /Ceramics International 30(2004)843-852 case, however, the weight increment of the deposit with timizing suspension composition with all MCAA and PVB time declines rapidly or even stops completely because the concentration levels was conducted with type HP Al2O3 density of electric current decreases due to increasing re- All MCAA concentration levels were also used with type sistance of the system. This problem does not appear in the 3YS ZrO2. The study of suspension sedimentation, sintering constant-current mode [6, 201 kinetics and mechanical properties of deposits was carried It has been established recently that in isopropanol suspen- out on only one selected concentration level of MCAA and sions stabilized with monochloroacetic acid the Al2O3 and PVB. The exact composition of all the suspensions used is ZrO particles have a negative charge [21]. Electrophoretic gIven in Table 2 deposition, which in such cases occurs on the anode, has not so far been described for these systems in the literature. 2. 3. Electrophoretic deposition The aim of the present work was therefore to prepare Al2O3 and ZrO2 deposits from isopropanol suspensions stabilized A schematic section through a horizontal electrophoretic with monochloroacetic acid. Attention was mainly focused cell is given in Fig. 1. The electrodes made of stainless on optimizing the suspension composition and describing steel with polished surface were at a constant distance of he sintering kinetics, resultant microstructure and mechan- 26 mm, their effective areas were in the shape of a trapezoid of 15 cm. The volume of suspension in the electrophoretic cell was 80 mL A stabilized source controlled by microcom- puter(E815, Consort, Belgium) was uised as the voltage and 2. Experimental current source. All experiments were conducted in the 5 mA constant-current mode 21. Materials The depositions employed to optimize the suspension composition(Section 3. 1) were performed by continuous The Al2O3 and ZrO2 ceramic powder materials used for electrophoretic deposition lasting 30 min electrophoretic deposition are summarized in Table 1. Iso- When studying the effect of suspension sedimentation on propanol(p a, Onex, Czech Republic) was used as the dis- the course of deposition(Section 3. 2), interrupted deposi persion medium for the preparation of the suspensions of tions taking a total of 60-80 min were performed. With ev- Al2O3 and ZrOz powders. Monochloroacetic acid(MCAA; ery interruption of the deposition the deposit thickness w p.a., Lachema, Czech Republic)was used as the stabilizing measured, namely at 18, 38 and 58 mm below the suspen- and dispersing aid and polyvinylbutyral(PVB, Butvar B79, sion level and subsequently the suspension was or was not Monsanto, USA) was used as a binder. The water content stirred In the case of deposition without stirring the drop in in the suspensions was reduced to minimum by drying the the suspension top level (which contrasted with the volume ceramic powders at 130C/2 h while isopropanol was dried of clear solvent without ceramic powder-the supernatant) over calcium for several hours and subsequently distilled un- was read during the deposition time. These readings were til its water content was less than 0.01%(as shown by gas used to establish the mean velocity of sedimentation(us) chromatography analysis The resultant shape of the deposit was determined by mea- suring its thickness at 22 equidistant vertical depths 2. 2. Suspension composition Deposits of a larger thickness, designed for the study f sintering (Section 3.3) and mechanical The suspensions were prepared by mixing 15 wt% of (Section 3. 4), were obtained by interrupted deposition, i.e Al2O or ZrO2 powder in 85 wt. of the liquid phase that a sequence of consecutive depositions from one suspension, was prepared by dissolving 1, 2, 5, 15 or 25 wt. of MCAa with the suspension stirred between every two depositions and (in the case of Al2O3 suspension)0, 1, 2 or 4 wt% of Every partial deposition lasted 5 min, the total deposition PVB in isopropanol. A complete factor experiment for op- time was 120-160 min Table 1 Ceramic powder materials used for electrophoretic deposition Marking Material Manufacturer Manufacturers marking Mean particle size(um)a Mean agglomerate Malakoff Ind (USA) RC HP DBM 0.47 UFX Malakoff Ind (USA) RC UFX DBM 0.33 ZrO, d Tosoh (Japan) TZ-3Y 3YS ZrO, d Tosoh(Japan) TZ-3YS Established by laser diffraction(Horiba LA-500, Japan) c With an addition of 0.05 wt% Mgo d Stabilized by 3 mol. Y203

844 K. Maca et al. / Ceramics International 30 (2004) 843–852 case, however, the weight increment of the deposit with time declines rapidly or even stops completely because the density of electric current decreases due to increasing re￾sistance of the system. This problem does not appear in the constant-current mode [6,20]. It has been established recently that in isopropanol suspen￾sions stabilized with monochloroacetic acid the Al2O3 and ZrO2 particles have a negative charge [21]. Electrophoretic deposition, which in such cases occurs on the anode, has not so far been described for these systems in the literature. The aim of the present work was therefore to prepare Al2O3 and ZrO2 deposits from isopropanol suspensions stabilized with monochloroacetic acid. Attention was mainly focused on optimizing the suspension composition and describing the sintering kinetics, resultant microstructure and mechan￾ical properties of these deposits. 2. Experimental 2.1. Materials The Al2O3 and ZrO2 ceramic powder materials used for electrophoretic deposition are summarized in Table 1. Iso￾propanol (p.a., Onex, Czech Republic) was used as the dis￾persion medium for the preparation of the suspensions of Al2O3 and ZrO2 powders. Monochloroacetic acid (MCAA; p.a., Lachema, Czech Republic) was used as the stabilizing and dispersing aid and polyvinylbutyral (PVB; Butvar B79, Monsanto, USA) was used as a binder. The water content in the suspensions was reduced to minimum by drying the ceramic powders at 130 ◦C/2 h while isopropanol was dried over calcium for several hours and subsequently distilled un￾til its water content was less than 0.01% (as shown by gas chromatography analysis). 2.2. Suspension composition The suspensions were prepared by mixing 15 wt.% of Al2O3 or ZrO2 powder in 85 wt.% of the liquid phase that was prepared by dissolving 1, 2, 5, 15 or 25 wt.% of MCAA and (in the case of Al2O3 suspension) 0, 1, 2 or 4 wt.% of PVB in isopropanol. A complete factor experiment for op￾Table 1 Ceramic powder materials used for electrophoretic deposition Marking Material Manufacturer Manufacturer’s marking Mean particle size (
m)a Mean agglomerate size (
m)b HP Al2O3 c Malakoff Ind. (USA) RC HP DBM 0.47 0.6 UFX Al2O3 c Malakoff Ind. (USA) RC UFX DBM 0.33 0.4 3Y ZrO2 d Tosoh (Japan) TZ-3Y 0.25 0.7 3YS ZrO2 d Tosoh (Japan) TZ-3YS 0.12 0.7 a Established from microphotographs. b Established by laser diffraction (Horiba LA-500, Japan). c With an addition of 0.05 wt.% MgO. d Stabilized by 3 mol.% Y2O3. timizing suspension composition with all MCAA and PVB concentration levels was conducted with type HP Al2O3. All MCAA concentration levels were also used with type 3YS ZrO2. The study of suspension sedimentation, sintering kinetics and mechanical properties of deposits was carried out on only one selected concentration level of MCAA and PVB. The exact composition of all the suspensions used is given in Table 2. 2.3. Electrophoretic deposition A schematic section through a horizontal electrophoretic cell is given in Fig. 1. The electrodes made of stainless steel with polished surface were at a constant distance of 26 mm, their effective areas were in the shape of a trapezoid of 15 cm2. The volume of suspension in the electrophoretic cell was 80 ml. A stabilized source controlled by microcom￾puter (E815, Consort, Belgium) was used as the voltage and current source. All experiments were conducted in the 5 mA constant-current mode. The depositions employed to optimize the suspension composition (Section 3.1) were performed by continuous electrophoretic deposition lasting 30 min. When studying the effect of suspension sedimentation on the course of deposition (Section 3.2), interrupted deposi￾tions taking a total of 60–80 min were performed. With ev￾ery interruption of the deposition the deposit thickness was measured, namely at 18, 38 and 58 mm below the suspen￾sion level and subsequently the suspension was or was not stirred. In the case of deposition without stirring the drop in the suspension top level (which contrasted with the volume of clear solvent without ceramic powder—the supernatant) was read during the deposition time. These readings were used to establish the mean velocity of sedimentation (vs). The resultant shape of the deposit was determined by mea￾suring its thickness at 22 equidistant vertical depths. Deposits of a larger thickness, designed for the study of sintering (Section 3.3) and mechanical properties (Section 3.4), were obtained by interrupted deposition, i.e. a sequence of consecutive depositions from one suspension, with the suspension stirred between every two depositions. Every partial deposition lasted 5 min, the total deposition time was 120–160 min

K. Maca et al. /Ceramics International 30(2004)843-852 Table 2 Al]O3(wt%) O Isopropanol(wt % MCAA(wt % VB(wt %) Used in section(s) HP-1-0 83.30 80.75 4.25 P-150 72.25 HP25-0 21.25 83.16 HP-2. 79.80 P-15-1 55555555555 71.4 12.60 HP-1-2 HP25-2 0.75 HP-1-4 555555 80.20 0.81 333333333 HP-25-4 3YS-5-0 3.1 3YS-15-0 00000 3.1,3.3,34 UFX-15-0 3Y-15-0 15 75 3.3.3.4 2. 4. Evaluation of deposit properties annealed(800C/1 h)and sintered (1500C/2 h)in ai All the deposits together with the electrodes were The quality of the deposit surface subsequent to drying first dried at room temperature for 24 h and at 70C for was evaluated visually. The relative density of the annealed I h, after which they were removed from the electrodes, deposit (Pgoo) was established from soaking capacity and the relative density of the sintered deposit(p1500) was estab- lished by the Archimedes method (EN 623-2). The pore size distribution was established by mercury porosimetry( Carlo supply Erba 200, Italy) The sintering process was monitored by a high-temperature dilatometer(L75/50, Linseis, Germany ) The relative length ge in the deposit as a function of time and temp was measured in two directions, namely in the direction of particle motion during electrophoretic deposition (longitu dinal direction-marked by index"L )and in perpendic ular direction to the particle motion during the deposit (transversal direction--marked by index"T). The dimen sionless coefficient of specimen shrinkage anisotropy (h) was calculated according to the relation where EL is the final deposit relative shrinkage in the longi tudinal direction, and ET is the final deposit relative shrin Fig. 1. Section through the cell used for electrophoretic deposition of age in the transversal direction. The coefficient of thermal expansion(CTE) was calculated from the cooling curves of

K. Maca et al. / Ceramics International 30 (2004) 843–852 845 Table 2 Composition of suspensions Suspension Al2O3 (wt.%) ZrO2 (wt.%) Isopropanol (wt.%) MCAA (wt.%) PVB (wt.%) Used in section(s) HP-1-0 15 0 84.15 0.85 0 3.1 HP-2-0 15 0 83.30 1.70 0 3.1 HP-5-0 15 0 80.75 4.25 0 3.1 HP-15-0 15 0 72.25 12.75 0 3.1, 3.2, 3.3, 3.4 HP-25-0 15 0 63.75 21.25 0 3.1 HP-1-1 15 0 83.16 0.84 1 3.1 HP-2-1 15 0 82.32 1.68 1 3.1 HP-5-1 15 0 79.80 4.20 1 3.1 HP-15-1 15 0 71.40 12.60 1 3.1 HP-25-1 15 0 63.00 21.00 1 3.1 HP-1-2 15 0 82.17 0.83 2 3.1 HP-2-2 15 0 81.34 1.66 2 3.1 HP-5-2 15 0 78.85 4.15 2 3.1 HP-15-2 15 0 70.56 12.45 2 3.1 HP-25-2 15 0 62.25 20.75 2 3.1 HP-1-4 15 0 80.20 0.81 4 3.1 HP-2-4 15 0 79.38 1.62 4 3.1 HP-5-4 15 0 76.95 4.05 4 3.1 HP-15-4 15 0 68.85 12.15 4 3.1 HP-25-4 15 0 60.75 20.25 4 3.1 3YS-1-0 0 15 84.15 0.85 0 3.1 3YS-2-0 0 15 83.30 1.70 0 3.1 3YS-5-0 0 15 80.75 4.25 0 3.1 3YS-15-0 0 15 72.25 12.75 0 3.1, 3.3, 3.4 3YS-25-0 0 15 63.75 21.25 0 3.1 UFX-15-0 15 0 72.25 12.75 0 3.3, 3.4 3Y-15-0 0 15 72.25 12.75 0 3.3, 3.4 2.4. Evaluation of deposit properties All the deposits together with the electrodes were first dried at room temperature for 24 h and at 70 ◦C for 1 h, after which they were removed from the electrodes, Fig. 1. Section through the cell used for electrophoretic deposition of ceramic materials. annealed (800 ◦C/1 h) and sintered (1500 ◦C/2 h) in air atmosphere. The quality of the deposit surface subsequent to drying was evaluated visually. The relative density of the annealed deposit (ρ800) was established from soaking capacity and the relative density of the sintered deposit (ρ1500) was estab￾lished by the Archimedes method (EN 623-2). The pore size distribution was established by mercury porosimetry (Carlo Erba 200, Italy). The sintering process was monitored by a high-temperature dilatometer (L75/50, Linseis, Germany). The relative length change in the deposit as a function of time and temperature was measured in two directions, namely in the direction of particle motion during electrophoretic deposition (longitu￾dinal direction—marked by index “L”) and in perpendic￾ular direction to the particle motion during the deposition (transversal direction—marked by index “T”). The dimen￾sionless coefficient of specimen shrinkage anisotropy (k) was calculated according to the relation: k = εT εL (1) where εL is the final deposit relative shrinkage in the longi￾tudinal direction, and εT is the final deposit relative shrink￾age in the transversal direction. The coefficient of thermal expansion (CTE) was calculated from the cooling curves of

K. Maca et al. /Ceramics International 30(2004)843-852 sintered deposits. The temperature dependence of relative specimen density(Prel (n)) was calculated from the values F of final densities and from the shrinkage curve ED(first, 5 PVB CONCENTRATION [ wt%1 ◇4w%(HPA2o Polished specimens of sintered deposits were thermally ·0w%(3Yszo2) etched and made conductive by applying three layers of gold coating and then studied by SEM (Philips XL30, the Nether lands). The grain size of sintered ceramics(dG )was deter- a ined by computer image analysis(Atlas Software, Tescan, 9 20 Czech Republic)from microphotographs of etched deposit ui sections. The value of equivalent diameter, calculated from he area of grains, was used as the mean grain size(dG) The indentation fracture toughness of sintered deposits MCAA CONCENTRATION [wt%] was measured by the indentation method (according to Japanese Industrial Standard JIs R 1607). The Vickers Fig. 2. Dependence of electric field intensity during deposition of alumina and zirconia on the concentration of MCAA and PvB in the suspension. hardness tester was used as the indentor. The fracture toughness(Kic) of materials was calculated using the val polyvinylbutyral in the suspension(see Fig. 2). The drop in ues of the length of indentation crack(c), indentation force the intensity of electric field with increasing concentration (F=98N), Youngs modulus of ZrO2(Ey 380 GP of monochloroacetic acid was probably due to the increas- [19])and Al2O3(Ey= 210 GPa [19]) and hardness(HV according to the relation given in JISR 1607. The hardness suspensions increased from 2. x 10-4Sm-I(HP-1-0)[21] of material was determined from the size of the diagonal of to 23. 8x 10-4Sm-(HP-25-0)[21]. The relation between the hardness tester tip indentation in the surface of material velocity of particle motion(u), electrophoretic mobility (u) caused by indentation force F and electric field intensity(E) is given by the equation The four-point flexure strength(EN 843-1)was only measured for Al2O3 deposits(type HP). The test speci U=×E. mens were cut with a diamond disk from deposits anneale at 1000"C/i h. The test specimens were then sintered at particles at an MCAA concentration of more than 0.85 wt% is independent of its concentration [211, the velocity of 2mm x 2.5 mm x 25 mm and the tensile side was polished the particles in the suspension decreased with decreasing with diamond paste of l um grain size. Ber electric field intensity and thus with ng mcaa con- was measured on a universal test machine(Z020, Zwick centration. The slower motion of particles probably led to Germany)with a jig for bending strength measurement their more effective arrangement on the anode, which was confirmed by the higher green density of deposits with a higher MCAA content(see Fig 3). The final relative deposit 3. Results and discussion 3.1. Optimization of suspension composition 5 冷D The suspensions with type HP AlzO3 and type 3YS ZrO2 vere used for the optimization experiments( see Table 2) The Al2O3 and ZrOz particles were charged negatively and he layer was deposited on the anode, in the same way as in a 62 green density (p work of Cihlar et al. [211 PVB CONCENTRATION [wt%] The smoothness of deposit surface, deposit thickness and density were affected by suspension composition 口1w%(FPA2) ( the contents of monochloroacetic acid and polyvinylbu- △2w%(AO) tyral). The deposit had a smooth surface if the deposition was from a suspension containing more than 4 wt. of monochloroacetic acid, irrespective of the PVB concentra- tion. This phenomenon was probably due to the effect of MCAA CONCENTRATION [wt% MCAA concentration on electrophoretic behaviour of the Fig 3. Dependence of the relative density of alumina deposit after an- suspension. The intensity of electric field during deposition nealing and sintering on the concentration of MCAA and PVB in the was dependent on the contents of monochloroacetic acid and

846 K. Maca et al. / Ceramics International 30 (2004) 843–852 sintered deposits. The temperature dependence of relative specimen density (ρrel(T)) was calculated from the values of final densities and from the shrinkage curve ε(T) (first, the specimen elongation due to simple thermal expansion of the material was subtracted from the elongation values measured). Polished specimens of sintered deposits were thermally etched and made conductive by applying three layers of gold coating and then studied by SEM (Philips XL30, the Nether￾lands). The grain size of sintered ceramics (dG) was deter￾mined by computer image analysis (Atlas Software, Tescan, Czech Republic) from microphotographs of etched deposit sections. The value of equivalent diameter, calculated from the area of grains, was used as the mean grain size (dG). The indentation fracture toughness of sintered deposits was measured by the indentation method (according to Japanese Industrial Standard JIS R 1607). The Vickers hardness tester was used as the indentor. The fracture toughness (KIC) of materials was calculated using the val￾ues of the length of indentation crack (c), indentation force (F = 98 N), Young’s modulus of ZrO2 (EY = 380 GPa [19]) and Al2O3 (EY = 210 GPa [19]) and hardness (HV) according to the relation given in JIS R 1607. The hardness of material was determined from the size of the diagonal of the hardness tester tip indentation in the surface of material caused by indentation force F. The four-point flexure strength (EN 843-1) was only measured for Al2O3 deposits (type HP). The test speci￾mens were cut with a diamond disk from deposits annealed at 1000 ◦C/1 h. The test specimens were then sintered at 1500 ◦C/2 h. The sintered specimens were ground to be 2 mm × 2.5 mm × 25 mm and the tensile side was polished with diamond paste of 1
m grain size. Bending strength was measured on a universal test machine (Z020, Zwick, Germany) with a jig for bending strength measurement. 3. Results and discussion 3.1. Optimization of suspension composition The suspensions with type HP Al2O3 and type 3YS ZrO2 were used for the optimization experiments (see Table 2). The Al2O3 and ZrO2 particles were charged negatively and the layer was deposited on the anode, in the same way as in work of Cihlar et al. [21]. The smoothness of deposit surface, deposit thickness and density were affected by suspension composition (the contents of monochloroacetic acid and polyvinylbu￾tyral). The deposit had a smooth surface if the deposition was from a suspension containing more than 4 wt.% of monochloroacetic acid, irrespective of the PVB concentra￾tion. This phenomenon was probably due to the effect of MCAA concentration on electrophoretic behaviour of the suspension. The intensity of electric field during deposition was dependent on the contents of monochloroacetic acid and Fig. 2. Dependence of electric field intensity during deposition of alumina and zirconia on the concentration of MCAA and PVB in the suspension. polyvinylbutyral in the suspension (see Fig. 2). The drop in the intensity of electric field with increasing concentration of monochloroacetic acid was probably due to the increas￾ing conductivity of the solution, which in the case of Al2O3 suspensions increased from 2.9×10−4 S m−1 (HP-1-0) [21] to 23.8 × 10−4 S m−1 (HP-25-0) [21]. The relation between velocity of particle motion (v), electrophoretic mobility (µ) and electric field intensity (E) is given by the equation: v = µ × E. (2) Since electrophoretic mobility of the Al2O3 and ZrO2 particles at an MCAA concentration of more than 0.85 wt.% is independent of its concentration [21], the velocity of the particles in the suspension decreased with decreasing electric field intensity and thus with increasing MCAA con￾centration. The slower motion of particles probably led to their more effective arrangement on the anode, which was confirmed by the higher green density of deposits with a higher MCAA content (see Fig. 3). The final relative deposit Fig. 3. Dependence of the relative density of alumina deposit after an￾nealing and sintering on the concentration of MCAA and PVB in the suspension

K. Maca et al. /Ceramics International 30(2004)843-852 3.2. Suspension sedimentation and its elimination PVB CONCENTRATION [wt%! O Ow%(HP AL-o The deposits obtained in the previous part of the work Wt% (HP Al,o were of non-constant thickness. which increased contin- ◇4w%(HPAO uously towards the bottom of electrophoretic cell. The reason lay in suspension sedimentation due to earth's grav- itation, which in the case of horizontal arrangement of the electrophoretic cell is perpendicular to the direction of elec- trophoretic force. The following experiments, which wer conducted with the HP-15-0 suspension on the basis of the results of the preceding section, had as their aim the de scription and elimination of suspension sedimentation and Its consequences. MCAA CONCENTRATION The first to be studied was deposition with the interrupted deposition mode, during which the deposit thickness was Fig. 4. Dependence of alumina and zirconia deposit weight on the con measured continuously but the suspension was not stirred centration of MCAA and PVB in the suspension. The dependence of deposit thickness on time at three depths below the suspension level is given in the graph of Fig. 5. It density was ca. 99.5% and was independent of both Pvb can be seen from the graph that after some time the deposit and MCAA concentration(provided MCAA concentration thickness values differed with the place of measurement be- exceeded 4 wt % cause sedimentation occurred in the suspension As can be seen from Fig. 2, the addition of polyvinyl To prevent the sedimentation of powder, the suspension butyral to the suspension led to a slight increase in electric had to be stirred. Since after 5 min of deposition without stir current intensity during deposition. As established in work ring no differences in deposit thickness could be observed of Cihlar et al. [21], increasing polyvinylbutyral content re- at the individual levels of measuring(see Fig. 5), the 5-min duced the electrophoretic mobility of particles, which led interval was chosen as appropriate for stirring the suspen- to a lower weight of the deposit. This result has also been sion. Fig. 6 gives the dependence of deposit thickness proved in the present work as can be seen from Fig. 4, which time as obtained for interrupted deposition with suspension illustrates the dependence of deposit weight on MCAA and stirring. It can be seen that the deposition was uniform at al PVB concentrations. The electrophoretic mobility of parti- the three levels observed In the case that particle concentra cles is given the Henry eq tion in the suspension in vertical direction does not change (the suspension does not sediment or it is stirred)the de ( pendence of deposit weight(m)on time(O) is given by the Zhang equation [24](mo is the initial weight of powder in where e is the permittivity of the medium, s is the zeta suspension and d is the distance between electrodes otential, n is the dynamic viscosity of the medium, and f(Rk-)is the function of the product of particle radius(R) m=mo(1 -e-uE/d) and the thickness of electric double layer(k-). The drop in the electrophoretic mobility of particles in the suspension was due to the reduction in the s-potential of particles and the increase in the viscosity of the medium caused by the content of polyvinylbutyral in the suspension [21] The addition of polyvinylbutyral had no positive effect on E-d.58 mm below supension le either the final deposit density(see Fig. 3)or the flatness of g their surfaces. Since it reduced the electrophoretic mobility 2 of particles in the suspension, it had a negative effect on deposit weight(Fig 4) From the viewpoint of the flatness of der which is important, for example, in the deposition of layered composites[23], the optimum amounts were 15 and 25 wt% of MCAA in isopropanol. At a concentration of 15 wt % of MCAA, the deposit yield was, of course, higher(see Fig. 4) On the basis of the above results the suspensions containing no PVB and with a 15 wt. content of mCAa in the liquid phase(i.e. 12.75 wt. in the suspension) were evaluated as Fig. 5. Dependence of alumina( type HP)deposit thickness on deposition optimum suspensions time and on the vertical position(non-stirred suspension

K. Maca et al. / Ceramics International 30 (2004) 843–852 847 Fig. 4. Dependence of alumina and zirconia deposit weight on the con￾centration of MCAA and PVB in the suspension. density was ca. 99.5% and was independent of both PVB and MCAA concentration (provided MCAA concentration exceeded 4 wt.%). As can be seen from Fig. 2, the addition of polyvinyl￾butyral to the suspension led to a slight increase in electric current intensity during deposition. As established in work of Cihlar et al. [21], increasing polyvinylbutyral content re￾duced the electrophoretic mobility of particles, which led to a lower weight of the deposit. This result has also been proved in the present work as can be seen from Fig. 4, which illustrates the dependence of deposit weight on MCAA and PVB concentrations. The electrophoretic mobility of parti￾cles is given by the Henry equation [22]: µ = 2 3 εζ η f(Rκ−1) (3) where ε is the permittivity of the medium, ζ is the zeta potential, η is the dynamic viscosity of the medium, and f(Rk−1) is the function of the product of particle radius (R) and the thickness of electric double layer (k−1). The drop in the electrophoretic mobility of particles in the suspension was due to the reduction in the ζ-potential of particles and the increase in the viscosity of the medium caused by the content of polyvinylbutyral in the suspension [21]. The addition of polyvinylbutyral had no positive effect on either the final deposit density (see Fig. 3) or the flatness of their surfaces. Since it reduced the electrophoretic mobility of particles in the suspension, it had a negative effect on deposit weight (Fig. 4). From the viewpoint of the flatness of deposit surface, which is important, for example, in the deposition of layered composites [23], the optimum amounts were 15 and 25 wt.% of MCAA in isopropanol. At a concentration of 15 wt.% of MCAA, the deposit yield was, of course, higher (see Fig. 4). On the basis of the above results the suspensions containing no PVB and with a 15 wt.% content of MCAA in the liquid phase (i.e. 12.75 wt.% in the suspension) were evaluated as optimum suspensions. 3.2. Suspension sedimentation and its elimination The deposits obtained in the previous part of the work were of non-constant thickness, which increased contin￾uously towards the bottom of electrophoretic cell. The reason lay in suspension sedimentation due to earth’s grav￾itation, which in the case of horizontal arrangement of the electrophoretic cell is perpendicular to the direction of elec￾trophoretic force. The following experiments, which were conducted with the HP-15-0 suspension on the basis of the results of the preceding section, had as their aim the de￾scription and elimination of suspension sedimentation and its consequences. The first to be studied was deposition with the interrupted deposition mode, during which the deposit thickness was measured continuously but the suspension was not stirred. The dependence of deposit thickness on time at three depths below the suspension level is given in the graph of Fig. 5. It can be seen from the graph that after some time the deposit thickness values differed with the place of measurement be￾cause sedimentation occurred in the suspension. To prevent the sedimentation of powder, the suspension had to be stirred. Since after 5 min of deposition without stir￾ring no differences in deposit thickness could be observed at the individual levels of measuring (see Fig. 5), the 5-min interval was chosen as appropriate for stirring the suspen￾sion. Fig. 6 gives the dependence of deposit thickness on time as obtained for interrupted deposition with suspension stirring. It can be seen that the deposition was uniform at all the three levels observed. In the case that particle concentra￾tion in the suspension in vertical direction does not change (the suspension does not sediment or it is stirred) the de￾pendence of deposit weight (m) on time (t) is given by the Zhang equation [24] (m0 is the initial weight of powder in suspension and d is the distance between electrodes): m = m0(1 − e−(µE/d)t) (4) Fig. 5. Dependence of alumina (type HP) deposit thickness on deposition time and on the vertical position (non-stirred suspension)

848 K. Maca et al. /Ceramics International 30(2004)843-852 △smn5 mm=2.78103(-em) 010203040506070B090 EEo=oEoso Fig. 6. Dependence of alumina(type HP) deposit thickness on deposition time and on the vertical position( the suspension was stirred at interva of 5 min) Across the whole of its area a deposit from such a sus pension should have a constant thickness h, which can b calculated from the relatie h (1-e-(E/o (5) Sptheor prel )deposit thickness on the height where S is the electrode surface, Ptheor is the theoretical ceramics density and prel is the relative deposit density after of electrophoretic cell and us is the sedimentation velocity deposition established as described in the experimental part and found As can be seen, the experimental data in Fig. 6 can be to be 0.75 mm min-I. Fig. 7 gives a comparison of the the- fitted well with the curve oretical calculated deposit shape with the experimentally h(mm)=278(1-e-0038m) (6) established shape subsequent to a 70-min deposition of Al2O3(type HP)without stirring the suspension. As can be Comparing Eq. (6)with Eq (5)(with S= 15 cm2,d seen, in the upper part of the electrode the deposit 26 mm, E =30.8 Vcm", Prel= 60%) the values mo= corresponded with the theoretical dependence but 10.0 g and u=0.475 um cm V-s were calculated. The lower part the deposit thickness was larger than it actual amount of particles in the suspension was 11.6g, be on the assumption that the ceramic powder settles on which was in good agreement with the calculated value the bottom. It seems that the powder did not settle on the 10.0g. The difference may have been due to partial sedi- bottom but whirled in the lower part of the cell and at the mentation of the powder, estimation of the relative deposit same time deposited on the electrode density from the density value of the dried specimen or the electrophoretic cell geometry, when part of the suspension 3.3. Sintering kinetics and the resultant microstructure of was behind the electrodes( see Fig. I). The calculated mo- Al2O3 and ZrO2 deposits bility value was in good agreement with the mobility u= 0.275 umcmV-s-I as established on a Zetasizer appara For the preparation of all the types of materials studied tus for a similar but 100x diluted suspension in ac electric below, interrupted electrophoretic deposition was used,cou- field [211 pled with suspension stirring at interrupted deposition er Now that we know the electrophoretic mobility of parti- ery 5min. The suspension contained 15 wt %of the ceramic cles in the suspension, we can venture a theoretical descrip- phase and 12.75 wt. of MCAA(see Table 2). The proper tion of the shape of deposit cross section in dependence on ties of the deposits established during sintering and by eval- time and on the depth below suspension level even for the uating their microstructure are summarized in Table ase of non-stirred, that is to say sedimenting suspension, The relative deposit density after annealing decreased with decreasing particle size. The relative density of Al2 O3 and h(mm)=2.78(1-c-00381-/s) ZrOz deposits after sintering was higher than 99%, with the exception of type UFX Al2O3 deposit, whose final relative where H(mm)is the initial height of suspension level density was ca. 98.6%. The Zro2 material reached almost 65 mm), x(mm) is the vertical distance from the botto the theoretical density although it exhibited very low green

848 K. Maca et al. / Ceramics International 30 (2004) 843–852 Fig. 6. Dependence of alumina (type HP) deposit thickness on deposition time and on the vertical position (the suspension was stirred at intervals of 5 min). Across the whole of its area a deposit from such a sus￾pension should have a constant thickness h, which can be calculated from the relation: h = 100 m0 Sρtheorρrel (1 − e−(µE/d)t) (5) where S is the electrode surface, ρtheor is the theoretical ceramics density and ρrel is the relative deposit density after deposition. As can be seen, the experimental data in Fig. 6 can be fitted well with the curve: h (mm) = 2.78(1 − e−0.0338·t (min) ) (6) Comparing Eq. (6) with Eq. (5) (with S = 15 cm2, d = 26 mm, E = 30.8 V cm−1, ρrel = 60%), the values m0 = 10.0 g and µ = 0.475
m cm V−1 s−1 were calculated. The actual amount of particles in the suspension was 11.6 g, which was in good agreement with the calculated value 10.0 g. The difference may have been due to partial sedi￾mentation of the powder, estimation of the relative deposit density from the density value of the dried specimen or the electrophoretic cell geometry, when part of the suspension was behind the electrodes (see Fig. 1). The calculated mo￾bility value was in good agreement with the mobility µ = 0.275
m cm V−1 s−1 as established on a Zetasizer appara￾tus for a similar but 100× diluted suspension in ac electric field [21]. Now that we know the electrophoretic mobility of parti￾cles in the suspension, we can venture a theoretical descrip￾tion of the shape of deposit cross section in dependence on time and on the depth below suspension level even for the case of non-stirred, that is to say sedimenting suspension, according to the relation: h (mm) = 2.78(1 − e−0.0338(H−x/vS) ) (7) where H (mm) is the initial height of suspension level (65 mm), x (mm) is the vertical distance from the bottom Fig. 7. Dependence of alumina (type HP) deposit thickness on the height from the bottom of electrophoretic cell. of electrophoretic cell and vS is the sedimentation velocity established as described in the experimental part and found to be 0.75 mm min−1. Fig. 7 gives a comparison of the the￾oretical calculated deposit shape with the experimentally established shape subsequent to a 70-min deposition of Al2O3 (type HP) without stirring the suspension. As can be seen, in the upper part of the electrode the deposit shape corresponded with the theoretical dependence but in the lower part the deposit thickness was larger than it would be on the assumption that the ceramic powder settles on the bottom. It seems that the powder did not settle on the bottom but whirled in the lower part of the cell and at the same time deposited on the electrode. 3.3. Sintering kinetics and the resultant microstructure of Al2O3 and ZrO2 deposits For the preparation of all the types of materials studied below, interrupted electrophoretic deposition was used, cou￾pled with suspension stirring at interrupted deposition ev￾ery 5 min. The suspension contained 15 wt.% of the ceramic phase and 12.75 wt.% of MCAA (see Table 2). The proper￾ties of the deposits established during sintering and by eval￾uating their microstructure are summarized in Table 3. The relative deposit density after annealing decreased with decreasing particle size. The relative density of Al2O3 and ZrO2 deposits after sintering was higher than 99%, with the exception of type UFX Al2O3 deposit, whose final relative density was ca. 98.6%. The ZrO2 material reached almost the theoretical density although it exhibited very low green

K. Maca et al. /Ceramics International 30(2004)843-852 Table 3 Selected properties of ceramic deposits after annealing and sintering Material type 0)shm(%-)ps00(%)shn(%-)k=erl(-)CTE×10-6(K-) 0.3/6 0.77 1.93 UFX-L 2.22 UFX-T 3YS-L 47.0 0.2/3 3Y-L 0.3/6 0.2/3 3Y.T 0.1/3 10.5 a s is standard deviation and n is number of measurements density. This is because the sinterability of a green body is not given by the absolute value of its porosity but by the pore size distribution, in particular by the ratio of the radius of the largest pores and the particle size [25, 26] A shrinkage anisotropy was found in Al2 O3 specimens in e the longitudinal direction(L) and in the transversal direction (n). Specimen shrinkage was higher in the direction of par- ticle motion ( L nkage anisotropy was also established HP ALO(EPD) for prism-shaped bodies prepared by injection moulding of 10 type HP Al2O3 powder [27] and another type of alumina powder [28], with the shrinkage in perpendicular direction to injection direction being higher. This anisotropy was explained by the longer axes of elongated Al2O3 particles being arranged in parallel with injection direction [28].Ac- 0.3750.50.75 1.52253.7557.510 cepting this hypothesis would mean that in the deposit the PORE DIAMETER [um particles settle with their longer dimension running parallel Fig. 9. Pore size distribution of alumina(type HP) prepared by elec- with the electrode plane although in the suspension the par- trophoretic deposition(EPD ), injection moulding(IM) and cold isosta ticles flow with their longer dimension perpendicular to the pressing(CIP) electrode to minimize the mediums resistance. Similarly Dalzell and Clark [29] observed a tendency of Sic fibres in Al2O3 matrix to be oriented in parallel to the electrode In work of Maca et al. [30], the coefficient of thermal In the rO2 deposits with spherical particles the shrinkage expansion of injection-moulded and isostatically pressed anisotropy during sintering was negligible Al2O3 of the type of HP was established, CTE(Al2O3)=9 x 10-6K-, and also of ZrO2 of the type of 3Y, prepared in the same way, CTE(ZrO2)=11 x 10-K. These values are approximated more by the values measured on specimens in the transversal direction. The values of the coefficients of thermal expansion in the longitudinal HP AL O3(EPD) tion carried a large measuring error since the length of the specimens was too small 吕 Although the specimen prepared by electrophoretic depo. sition was of low green density, its sintering kinetics was comparable with that of the specimen prepared by cold iso- static pressing, and better than in the case of the specimen prepared by injection moulding(Fig. 8). This means that m:T:m:.:-:TmIT/mi he arrangement of particles and pores in the course of elec trophoretic deposition was homogeneous, which was also 1200 1400 1600 confirmed by mercury porosimetry of green bodies(Fig 9) Fig. 10 gives the photographs of the microstructure of Fig 8. Sintering kinetics of alumina(type HP) prepared by electrophoretic Al2O3 and Zro deposits. The mean grain size(dG)es deposition(EPD), injection moulding (IM)and cold isostatic press tablished by image analysis from the microstructure pho- tographs is given in Table 3. The size of Al2O3 grains was

K. Maca et al. / Ceramics International 30 (2004) 843–852 849 Table 3 Selected properties of ceramic deposits after annealing and sintering Material type ρ800 (%) s/n (%/−) a ρ1500 (%) s/n (%/−) a k = εT /εL (−) CTE × 10−6 (K−1) dG (
m) HP-L 62.2 0.3/6 99.2 0.2/3 0.77 8.7 1.93 HP-T 99.2 0.1/3 9.0 UFX-L 58.5 0.3/6 98.5 0.4/3 0.81 9.3 2.22 UFX-T 98.7 0.1/3 9.1 3YS-L 47.0 0.2/6 99.6 0.8/3 0.96 9.7 0.55 3YS-T 99.7 0.2/3 10.7 3Y-L 41.6 0.3/6 99.8 0.2/3 0.98 9.5 0.55 3Y-T 99.9 0.1/3 10.5 a s is standard deviation and n is number of measurements. density. This is because the sinterability of a green body is not given by the absolute value of its porosity but by the pore size distribution, in particular by the ratio of the radius of the largest pores and the particle size [25,26]. A shrinkage anisotropy was found in Al2O3 specimens in the longitudinal direction (L) and in the transversal direction (T). Specimen shrinkage was higher in the direction of par￾ticle motion (L). Shrinkage anisotropy was also established for prism-shaped bodies prepared by injection moulding of type HP Al2O3 powder [27] and another type of alumina powder [28], with the shrinkage in perpendicular direction to injection direction being higher. This anisotropy was explained by the longer axes of elongated Al2O3 particles being arranged in parallel with injection direction [28]. Ac￾cepting this hypothesis would mean that in the deposit the particles settle with their longer dimension running parallel with the electrode plane although in the suspension the par￾ticles flow with their longer dimension perpendicular to the electrode to minimize the medium’s resistance. Similarly, Dalzell and Clark [29] observed a tendency of SiC fibres in Al2O3 matrix to be oriented in parallel to the electrode. In the ZrO2 deposits with spherical particles the shrinkage anisotropy during sintering was negligible. Fig. 8. Sintering kinetics of alumina (type HP) prepared by electrophoretic deposition (EPD), injection moulding (IM) and cold isostatic pressing (CIP). Fig. 9. Pore size distribution of alumina (type HP) prepared by elec￾trophoretic deposition (EPD), injection moulding (IM) and cold isostatic pressing (CIP). In work of Maca et al. [30], the coefficient of thermal expansion of injection-moulded and isostatically pressed Al2O3 of the type of HP was established, CTE (Al2O3) = 9 × 10−6 K−1, and also of ZrO2 of the type of 3Y, prepared in the same way, CTE(ZrO2) = 11 × 10−6 K−1. These values are approximated more by the values measured on specimens in the transversal direction. The values of the coefficients of thermal expansion in the longitudinal direc￾tion carried a large measuring error since the length of the specimens was too small. Although the specimen prepared by electrophoretic depo￾sition was of low green density, its sintering kinetics was comparable with that of the specimen prepared by cold iso￾static pressing, and better than in the case of the specimen prepared by injection moulding (Fig. 8). This means that the arrangement of particles and pores in the course of elec￾trophoretic deposition was homogeneous, which was also confirmed by mercury porosimetry of green bodies (Fig. 9). Fig. 10 gives the photographs of the microstructure of Al2O3 and ZrO2 deposits. The mean grain size (dG) es￾tablished by image analysis from the microstructure pho￾tographs is given in Table 3. The size of Al2O3 grains was

K. Maca et al. /Ceramics International 30(2004)843-852 3 μm Fig. 10. Microstructure of sintered alumina and zirconia ceramics prepared by intermittent electrophoretic deposition: (a) type HP alumina,(b) type UFX alumina,(c) type 3YS zirconia and(d) type 3Y zirconia. ss, indentation crack length and fracture toughness of Al2O3 and ZrO2 deposits Indentation crack length HV(GPa) le(um) s(um/n KIc(MPamo-s s(MPamsn UFX 0.6/20 3YS 0.1/20 8.6 9.6 0.720 ca 2 um while the grain size of type 3YS ZrO2 and type hardness of type HP Al2O3 deposit and that of type UFX 3Y ZrO was 0.55 um. The slight increase in ZrO grains Al2O3 deposit was practically the same, 17.9 and 18.0 GPa, when compared with the initial powder size was not surpris- respectively. The hardness of ZrO2 deposits was also iden- ing, it was also observed by other authors [31] and it was tical: 12.9 GPa for both types of Zro2. The hardness values explained as the effect of its tetragonal structure on the mo- of the deposits are comparable with the values given in the bility of grain boundaries. For comparison, the grain size literature: 18 GPa in the case of Al2 O3 [33] and 12. 4 GPa in of type HP Al2O3 prepared by injection moulding and sin- the case of Zro2 [34 tering at 1530 C/2 h was 1.6 um, that of type 3YS ZrO2 The Zro2 deposits exhibited higher fracture toughness prepared by injection moulding and sintering at 1500 C/2h than the Al2O3 deposits, which is an anticipated result, was 0.4 um(established by linear intercept method)[32] caused by transformation toughening with yttria-stabilized 3. 4. Mechanical properties of Al2 O3 and ZrO2 The mean bending strength om of type HP Al2O3 pre- pared by interrupted electrophoretic deposition in four-point flexure was 625 MPa with standard deviation s=87 MPa The hardness, indentation crack length and fracture tough- The strength values of bodies were described by the less of Al2O3 and ZrO2 deposits are given in Table 4. The Weibull probability distribution, with the corresponding

850 K. Maca et al. / Ceramics International 30 (2004) 843–852 Fig. 10. Microstructure of sintered alumina and zirconia ceramics prepared by intermittent electrophoretic deposition: (a) type HP alumina, (b) type UFX alumina, (c) type 3YS zirconia and (d) type 3Y zirconia. Table 4 Hardness, indentation crack length and fracture toughness of Al2O3 and ZrO2 deposits Material type Hardness Indentation crack length Fracture toughness HV (GPa) s (Pa)/n Ic (
m) s (
m)/n KIC (MPa m0.5) s (MPa m0.5)/n HP 17.8 0.5/20 138 17/20 5.2 1.1/20 UFX 18.0 0.6/20 123 11/20 6.0 0.7/20 3YS 12.9 0.1/20 89 6/20 8.6 0.9/20 3Y 12.9 0/20 82 4/20 9.6 0.7/20 ca. 2
m while the grain size of type 3YS ZrO2 and type 3Y ZrO2 was 0.55
m. The slight increase in ZrO2 grains when compared with the initial powder size was not surpris￾ing, it was also observed by other authors [31] and it was explained as the effect of its tetragonal structure on the mo￾bility of grain boundaries. For comparison, the grain size of type HP Al2O3 prepared by injection moulding and sin￾tering at 1530 ◦C/2 h was 1.6
m, that of type 3YS ZrO2 prepared by injection moulding and sintering at 1500 ◦C/2 h was 0.4
m (established by linear intercept method) [32]. 3.4. Mechanical properties of Al2O3 and ZrO2 deposits The hardness, indentation crack length and fracture tough￾ness of Al2O3 and ZrO2 deposits are given in Table 4. The hardness of type HP Al2O3 deposit and that of type UFX Al2O3 deposit was practically the same, 17.9 and 18.0 GPa, respectively. The hardness of ZrO2 deposits was also iden￾tical: 12.9 GPa for both types of ZrO2. The hardness values of the deposits are comparable with the values given in the literature: 18 GPa in the case of Al2O3 [33] and 12.4 GPa in the case of ZrO2 [34]. The ZrO2 deposits exhibited higher fracture toughness than the Al2O3 deposits, which is an anticipated result, caused by transformation toughening with yttria-stabilized ZrO2. The mean bending strength σm of type HP Al2O3 pre￾pared by interrupted electrophoretic deposition in four-point flexure was 625 MPa with standard deviation s = 87 MPa. The strength values of bodies were described by the Weibull probability distribution, with the corresponding

K. Maca et al. /Ceramics International 30(2004)843-852 strength value amo= 662 MPa and the Weibull distribu- uIspensions-l. Basic concepts and application to zirconia, J. Eur. tion parameter mw =8.6. The bending strength of Al2O3 eram.Soc.18(1998)675-683 prepared by electrophoretic deposition was examined on [6]F. Harbach, H. Nienburg, Homogenous functional ceran bodies of2mm×2.5mm×20mm. With the aid of the ponents through electrophoretic deposition from stabl colloidal suspensions-ll. Beta-alumina and concepts for industrial produc- loaded volume unit [35] the bending strength value found tion,J. Eur. Ceram Soc. 18(1998)685-692 for bodies of2mm×2.5mm×20 mm can be converted [7 T. Uchikoshi, K. Ozawa, B D. Hatton, Y. Sakka, Dense, bubble-free to the bending strength value corresponding to bodies of eramic deposits from aqueous suspensions by electrophoretic depo 3 mm x 4 mm x 40 mm. After this recalculation the bending sition, J Mater. Res. 16(2001)321-324 strength of alumina prepared by electrophoretic deposi [8]JY. Choudhary, H.S. Ray, K.N. Rai, Electrophoretic deposition of alumina from aqueous suspensions, Trans. J. Br. Ceram. Soc. 81 tion was omo 553 MPa. This bending strength value (1982)189193 was comparable with those of type HP Al2O3 prepared by [9]R. Clasen,S Janes, Ch. Oswald, D. Ranker, Electrophoretic depo injection moulding(515 MPa) and cold isostatic pressing sition of nanosized ceramic powders, Adv. Ceram. 21(1987)481 (464MPa) [10] P, Sarkar, P.S. Nich (1996)1987-2002 4. Conclusion [11]1. Zhitomirski, Electrophoretic and electrolytic deposition of ceramic gs on carbon fibers, J. Eur. Ceram Soc. 18(1998)849-856 Electrophoretic deposition of alumina and zirconia from [12]J. Will, M. Hruschka, L. Gubler, L.J. Gauckler, Electrophoretic de- isopropanol suspension in the presence of monochloroacetic position of zirconia on porous anodic substrates, J. Am. Ceram Soc acid using 5 mA constant current occurred on the anode 84(2001)328-332 [13]T. Ishihara, K. Sato, Y. Takita, Electrophoretic deposition of With increasing content of monochloroacetic acid in the 203-stabilized ZrO2 electrolyte films in solid oxide fuel cells, J suspension the electric field intensity necessary to gen- Am. Ceram.Soc.79(1996)913-919 erate a constant current of 5 ma decreased, leading to a [14]. Ishihara, K Shimose, T Kudo, H Nishiguchi, T. Akbay, Y. Takita, of e particles a nd a more effective ar- reparation of yttria-stabilized zirconia thin films on strontium-doped rangement of these particles on the electrode. With the LaMnO cathode substrates via electropho xide fuel cells, J. Am. Ceram. Soc. 83(2000)1921-1927 content of monochloroacetic acid in the suspension exceed- [15]F Chen, M. Liu ing 12 15 wt % deposits with flat surface were obtained SM)and LSM-Ysz subtzed(YSz)ilms on which sintered at 1500 C to a density higher than 99% TD trophoretic deposition(EPD)method, J. Eur. Ceram. Soc. 21(2001) The electrophoretic mobility of alumina particles in this suspension was 0.48 mcm v-s- [16]RN. Basu, C.A. Randall, M.J. Mayo, Fabrication of dense zirconia electrolyte film for tubular solid oxide fuel cells by electrophoretic The hardness, bending strength and fracture toughness deposition, J. Am. Ceram. Soc. 84(2001)33-40. of electrophoretically deposited Al2O3 and ZrO2 materials [17]P. Sarkar, X Haung, P.S. Nicholson, Structural ceramic microlami- were comparable with the values given in the literature and nates by electrophoretic deposition, J. Am. Ceram Soc. 75(1999) EPD is therefore an effective way to produce low cost com- 2907-2909 ponents with good properties [18]O. Prakash, P. Sarkar, P.S. Nicholson, Crack deflection in ceramic/ ceramic laminates with strong interfaces, J. Am. Ceram. Soc. 78 1995)1125-1127 [ 19B. Hatton, P.S. Nicholson, Design and fracture of layered Acknowledgements Al2O3/TZ3Y composites produced by electrophoretic deposition, J. Ceram.Soc.84(2001)571-576 This work was supported by the Czech Ministry of Edu- 220] P.S. Nicholson, P. Sarkar, The electrophoretic deposition of ceramics cation by the grant No. VZ CEZ: J22/98 Adv. Ceram.21(1987)469-479 [21]J. Cihlar, Z. Cihlarova, H. Hadraba, Influence of weak acids on electrophoretic behavior of alcoholic of alumina and zirconia, submitted for publication. References 22] P.C. Hiemenz, R. Rajagopalan, Principles of Colloid and Surface Chemistry, Marcel Dekker, New York, 1997 23H. Hadraba, K. Maca, J. Cihlar, Electrophoretic deposition of alumin []N. Ogata, J. Van Tassel, C A. Randall, Electrode formation by elec- nd zirconia-ll. Two-component systems, Ceram. Int. 30(2004) phoretic deposition of nanopowders, Mater. Lett. 49(2001)7 853-863 24Z. Zhang, Y. Huang, Z Jiang, Electrophoretic deposition forming [2]L Biao Lai, D.-H. Chen, T-C. Huang, Prepar and characteriza. of Sic-TZP composites in a nonaqueous sol media, J. Am. Ceram. tion of Ti-supported nanostructured Pt electrodes by electrophoretic deposition, Mater Res. Bull. 36(2001)1049-1055. [25]J. Zheng, J.S. Reed, Effects of particle packing 3]1. Zhitomirski, Cathodic electrophoretic deposition of diamond par- solid-state sintering, J. Am. Ceram. Soc. 72(1989)810-817. es, Mater. Lett. 37(1998)72-78 [26] M.N. Rahaman, L.C. De Jonghe, M.-Y. Chu, Effect of green density S.B. Lei, S.H. Chen, H.Y. Ma, S.Y. Wang, Assembly n densification and creep during sintering, J. Am. Ceram. Soc. 74 ensional ordered monolayers of (1991)514-519 deposition, Colloid Polym. Sci. 278(2000)682-686 27]M. Trunec, J. Cihlar, Thermal removal of multicomponent binder h, H. Nienburg, Homogenous functi from ceramic injection mouldings, J. Eur. Ceram. Soc. 22(2002) ponents through electrophoretic deposition from stable colloidal 2231-2241

K. Maca et al. / Ceramics International 30 (2004) 843–852 851 strength value σm0 = 662 MPa and the Weibull distribu￾tion parameter mW = 8.6. The bending strength of Al2O3 prepared by electrophoretic deposition was examined on bodies of 2 mm × 2.5 mm × 20 mm. With the aid of the loaded volume unit [35] the bending strength value found for bodies of 2 mm × 2.5 mm × 20 mm can be converted to the bending strength value corresponding to bodies of 3 mm ×4 mm ×40 mm. After this recalculation the bending strength of alumina prepared by electrophoretic deposi￾tion was σm0 = 553 MPa. This bending strength value was comparable with those of type HP Al2O3 prepared by injection moulding (515 MPa) and cold isostatic pressing (464 MPa). 4. Conclusion Electrophoretic deposition of alumina and zirconia from isopropanol suspension in the presence of monochloroacetic acid using 5 mA constant current occurred on the anode. With increasing content of monochloroacetic acid in the suspension the electric field intensity necessary to gen￾erate a constant current of 5 mA decreased, leading to a lower velocity of the particles and a more effective ar￾rangement of these particles on the electrode. With the content of monochloroacetic acid in the suspension exceed￾ing 12.15 wt.%, deposits with flat surface were obtained which sintered at 1500 ◦C to a density higher than 99% TD. The electrophoretic mobility of alumina particles in this suspension was 0.48
m cm V−1 s−1. The hardness, bending strength and fracture toughness of electrophoretically deposited Al2O3 and ZrO2 materials were comparable with the values given in the literature and EPD is therefore an effective way to produce low cost com￾ponents with good properties. Acknowledgements This work was supported by the Czech Ministry of Edu￾cation by the Grant No. VZ CEZ: J22/98. References [1] N. Ogata, J. Van Tassel, C.A. Randall, Electrode formation by elec￾trophoretic deposition of nanopowders, Mater. Lett. 49 (2001) 7– 14. [2] L. Biao Lai, D.-H. Chen, T.-C. Huang, Preparation and characteriza￾tion of Ti-supported nanostructured Pt electrodes by electrophoretic deposition, Mater. Res. Bull. 36 (2001) 1049–1055. [3] I. Zhitomirski, Cathodic electrophoretic deposition of diamond par￾ticles, Mater. Lett. 37 (1998) 72–78. [4] S.Y. Zhao, S.B. Lei, S.H. Chen, H.Y. Ma, S.Y. Wang, Assembly of two-dimensional ordered monolayers of nanoparticles by elec￾trophoretic deposition, Colloid Polym. Sci. 278 (2000) 682–686. [5] F. Harbach, H. Nienburg, Homogenous functional ceramic com￾ponents through electrophoretic deposition from stable colloidal suspensions—I. Basic concepts and application to zirconia, J. Eur. Ceram. Soc. 18 (1998) 675–683. [6] F. Harbach, H. Nienburg, Homogenous functional ceramic com￾ponents through electrophoretic deposition from stable colloidal suspensions—II. Beta-alumina and concepts for industrial produc￾tion, J. Eur. Ceram. Soc. 18 (1998) 685–692. [7] T. Uchikoshi, K. Ozawa, B.D. Hatton, Y. Sakka, Dense, bubble-free ceramic deposits from aqueous suspensions by electrophoretic depo￾sition, J. Mater. Res. 16 (2001) 321–324. [8] J.Y. Choudhary, H.S. Ray, K.N. Rai, Electrophoretic deposition of alumina from aqueous suspensions, Trans. J. Br. Ceram. Soc. 81 (1982) 189–193. [9] R. Clasen, S. Janes, Ch. Oswald, D. Ranker, Electrophoretic depo￾sition of nanosized ceramic powders, Adv. Ceram. 21 (1987) 481– 486. [10] P. Sarkar, P.S. Nicholson, Electrophoretic deposition (EPD): mecha￾nism, kinetics and application to ceramics, J. Am. Ceram. Soc. 79 (1996) 1987–2002. [11] I. Zhitomirski, Electrophoretic and electrolytic deposition of ceramic coatings on carbon fibers, J. Eur. Ceram. Soc. 18 (1998) 849–856. [12] J. Will, M. Hruschka, L. Gubler, L.J. Gauckler, Electrophoretic de￾position of zirconia on porous anodic substrates, J. Am. Ceram. Soc. 84 (2001) 328–332. [13] T. Ishihara, K. Sato, Y. Takita, Electrophoretic deposition of Y2O3-stabilized ZrO2 electrolyte films in solid oxide fuel cells, J. Am. Ceram. Soc. 79 (1996) 913–919. [14] T. Ishihara, K. Shimose, T. Kudo, H. Nishiguchi, T. Akbay, Y. Takita, Preparation of yttria-stabilized zirconia thin films on strontium-doped LaMnO3 cathode substrates via electrophoretic deposition for solid oxide fuel cells, J. Am. Ceram. Soc. 83 (2000) 1921–1927. [15] F. Chen, M. Liu, Preparation of yttria-stabilized (YSZ) films on La0.85Sr0.15MnO3 (LSM) and LSM-YSZ substrates using an elec￾trophoretic deposition (EPD) method, J. Eur. Ceram. Soc. 21 (2001) 127–134. [16] R.N. Basu, C.A. Randall, M.J. Mayo, Fabrication of dense zirconia electrolyte film for tubular solid oxide fuel cells by electrophoretic deposition, J. Am. Ceram. Soc. 84 (2001) 33–40. [17] P. Sarkar, X. Haung, P.S. Nicholson, Structural ceramic microlami￾nates by electrophoretic deposition, J. Am. Ceram. Soc. 75 (1999) 2907–2909. [18] O. Prakash, P. Sarkar, P.S. Nicholson, Crack deflection in ceramic/ ceramic laminates with strong interfaces, J. Am. Ceram. Soc. 78 (1995) 1125–1127. [19] B. Hatton, P.S. Nicholson, Design and fracture of layered Al2O3/TZ3Y composites produced by electrophoretic deposition, J. Am. Ceram. Soc. 84 (2001) 571–576. [20] P.S. Nicholson, P. Sarkar, The electrophoretic deposition of ceramics, Adv. Ceram. 21 (1987) 469–479. [21] J. Cihlar, Z. Cihlarova, H. Hadraba, Influence of weak acids on electrophoretic behavior of alcoholic suspensions of alumina and zirconia, submitted for publication. [22] P.C. Hiemenz, R. Rajagopalan, Principles of Colloid and Surface Chemistry, Marcel Dekker, New York, 1997. [23] H. Hadraba, K. Maca, J. Cihlar, Electrophoretic deposition of alumina and zirconia—II. Two-component systems, Ceram. Int. 30 (2004) 853–863. [24] Z. Zhang, Y. Huang, Z. Jiang, Electrophoretic deposition forming of SiC-TZP composites in a nonaqueous sol media, J. Am. Ceram. Soc. 77 (1994) 1946–1949. [25] J. Zheng, J.S. Reed, Effects of particle packing characteristics on solid-state sintering, J. Am. Ceram. Soc. 72 (1989) 810–817. [26] M.N. Rahaman, L.C. De Jonghe, M.-Y. Chu, Effect of green density on densification and creep during sintering, J. Am. Ceram. Soc. 74 (1991) 514–519. [27] M. Trunec, J. Cihlar, Thermal removal of multicomponent binder from ceramic injection mouldings, J. Eur. Ceram. Soc. 22 (2002) 2231–2241

K. Maca et al. /Ceramics International 30(2004)843-852 28S. Krug, J.R.G. Evans, J HH. ter Maat, Differential sintering in 32K. Maca, H. Hadraba, J. Cihlar, Study of sintering of oxide ceramic injection moulding: particle orientation effect, J. Eur. Ceram s of rate-controll ing method, in: G. Mueller(Ed ) Ceramics-Processing, Re 29]wJ. Dalzell, D E. Clark, Thermophoretic and electrophoretic deposi Tribology and Wear, Wiley, VCH, 2000, pp 161-166 tion of sol-gel composite coatings, Ceram. Eng. Sci. Proc. 7(1986) [33]A. Krell, A new look at grain size and load effects in the hardness 1014-1026. of ceramics, Mater. Sci. Eng. A 245(1998)277-284 B0]K Maca, H. Hadraba, J. Cihlar, Study of sintering of ceramics by [ 34]C. Zhao, J. Vleugels, L. Vandeperre, B. Basu, O. Van Der Biest, means of high-temperature dilatometry, Ceramics-Silikaty 42(1998) Y-TZP/Ce-TZP functionally graded composite, J. Mater. Sci. Lett. 151-158 17(1998)1453-1455 31M.J. Mayo, Processing of nanocrystalline ceramics from ultrafine 35] D.R. Bush, Designing ceramics components for structural applic articles, Int Mater. Rev. 41(1996)85-115. ons, J Mater. Eng Perform. 2(1993)851-862

852 K. Maca et al. / Ceramics International 30 (2004) 843–852 [28] S. Krug, J.R.G. Evans, J.H.H. ter Maat, Differential sintering in ceramic injection moulding: particle orientation effect, J. Eur. Ceram. Soc. 22 (2002) 173–181. [29] W.J. Dalzell, D.E. Clark, Thermophoretic and electrophoretic deposi￾tion of sol–gel composite coatings, Ceram. Eng. Sci. Proc. 7 (1986) 1014–1026. [30] K. Maca, H. Hadraba, J. Cihlar, Study of sintering of ceramics by means of high-temperature dilatometry, Ceramics-Silikáty 42 (1998) 151–158. [31] M.J. Mayo, Processing of nanocrystalline ceramics from ultrafine particles, Int. Mater. Rev. 41 (1996) 85–115. [32] K. Maca, H. Hadraba, J. Cihlar, Study of sintering of oxide ceramics at constant rate of heating and by means of rate-controlled sinter￾ing method, in: G. Mueller (Ed.), Ceramics-Processing, Reliability, Tribology and Wear, Wiley, VCH, 2000, pp. 161–166. [33] A. Krell, A new look at grain size and load effects in the hardness of ceramics, Mater. Sci. Eng. A 245 (1998) 277–284. [34] C. Zhao, J. Vleugels, L. Vandeperre, B. Basu, O. Van Der Biest, Y-TZP/Ce-TZP functionally graded composite, J. Mater. Sci. Lett. 17 (1998) 1453–1455. [35] D.R. Bush, Designing ceramics components for structural applica￾tions, J. Mater. Eng. Perform. 2 (1993) 851–862