ELECTROPHORETIC DEPOSITION: FUNDAMENTALS AND APPLICATIONS JOURNAL OF MATERIALS SCIENCE 39(2004)803-81I Electrophoretic deposition from aqueous suspensions for near-shape manufacturing of advanced ceramics and glasses-applications J. TABELLION R CLASEN Department of Powder Technology, Saarland University, Bd. 43, D-66123 Saarbrucken, Germany E-mail: j. tabellion@matsci uni sb.de Due to high deposition rates and the avoidance of inflammable, often hazardous organic solvents EPD from aqueous suspensions is a fast and low-cost shaping technique for ceramics and glasses. Since the deposition rate is independent of particle size EPd has an outstanding ability for the shaping of nano-particles. In this paper the shaping of complex silica glass and zirconia components, like tubes or structured parts by means of the membrane method is shown. Three-dimensional shaped porous polymer moulds were used as ion-permeable deposition surface. To enable near-shape manufacturing, mixtures inosized and microsized particles were electrophoretically deposited. No size-dependent separation was observed. Due to the very high green density of these green bodies (up to 84% of the theoretical value) shrinkage could be reduced to 4.7%. Not only oxide ceramics but also silicon carbide was deposited from aqueous suspensions. Apart from bulk SiC, protective coatings with a thickness of app. 60 um were applied on top of CFC substrates by EPD. Good adhesion was observed and no cracking occurred. Furthermore, electrophoretic impregnation was used for the modification of porous green bodies. Thus silica glasses with graded density and pore size as well as functionally graded composites were prepared. C 2004 Kluwer Academic Publishers 1. Introduction have to be applied to achieve acceptable shaping times Electrophoretic deposition(EPD)is a process known Furthermore, severe safety precautions have to be met, for decades [l], where charged particles move under if organic, often inflammable dispersants are used, es- the influence of a direct electric field towards an op- pecially in case of high voltages and/or high current positely charged electrode and coagulate there to form densities. As a consequence the process cost increases a stable deposit. Although EPD has been applied on Finally, disposal of hazardous organic waste and treat an industrial scale for years as enamelling and lacquer- ment of the suspensions for recovery of the dispersant ing technique( cataphoresis)[2, 3], it is not yet estab- as well as the absorption of volatile cracking produ lished as a shaping process for functional ceramics and during heat treatment can prevent the introduction of glasses. Among the ceramic coatings applied by Epd an EPD facility into an existing production line are e.g., phosphors [4], coatings for SOFCs [5], pho- As an alternative aqueous susp ons can be used tovoltaic applications [6] or insulating layers [7]. In for the EPD of ceramics. Since only water is used as some cases even manufacturing on an industrial scale dispersant, no sophisticated safety precautions are nec- has become likely [8] essary and treatment of the suspensions after EPD is But in case of bulk ceramic or glass components no easy. Most important, very high deposition rates can industrial manufacturing process has proved success- be reached for comparably low applied electric field ful so far. Nevertheless, several ceramic systems were strengths [16]. Thus process times can be reduced to investigated on a laboratory scale, including alumina several seconds to minutes depending on the material [9], zirconia [101, SiC [ll, 12] and PZT [13]. Compre- used. Clay components with a thickness of 10 mm could hensive reviews about EPD as shaping technique for be shaped from aqueous sanitary slips within 15s[17] ceramics are given in [14, 15]. In all of these cases or- But the only industrial attempt to produce tiles by EPD ganic solvents were used as dispersant, which seems to from aqueous suspensions [ 18] failed be one of the problems why EPD has never established The main problem associated with the use of aque yet for large-scale production of ceramics. First of all, ous suspensions for EPD, is the electrolysis-induced de- the deposition rates are significantly lower in compar- composition of water above a DC voltage of about 1. 4V ison with aqueous suspensions because of the much The electrolysis results in a movement of ions towards lower permittivity, thus very high electric field strengths the oppositely charged electrode, where recombination 0022-2461 2004 Kluwer Academic PublishersELECTROPHORETIC DEPOSITION: FUNDAMENTALS AND APPLICATIONS JOURNAL OF MATERIALS SCIENCE 3 9 (2 0 0 4 ) 803 – 811 Electrophoretic deposition from aqueous suspensions for near-shape manufacturing of advanced ceramics and glasses—applications J. TABELLION, R. CLASEN Department of Powder Technology, Saarland University, Bd. 43, D-66123 Saarbrucken, Germany E-mail: j.tabellion@matsci.uni.sb.de Due to high deposition rates and the avoidance of inflammable, often hazardous organic solvents EPD from aqueous suspensions is a fast and low-cost shaping technique for ceramics and glasses. Since the deposition rate is independent of particle size EPD has an outstanding ability for the shaping of nano-particles. In this paper the shaping of complex silica glass and zirconia components, like tubes or structured parts by means of the membrane method is shown. Three-dimensional shaped porous polymer moulds were used as ion-permeable deposition surface. To enable near-shape manufacturing, mixtures of nanosized and microsized particles were electrophoretically deposited. No size-dependent separation was observed. Due to the very high green density of these green bodies (up to 84% of the theoretical value) shrinkage could be reduced to 4.7%. Not only oxide ceramics but also silicon carbide was deposited from aqueous suspensions. Apart from bulk SiC, protective coatings with a thickness of app. 60 µm were applied on top of CFC substrates by EPD. Good adhesion was observed and no cracking occurred. Furthermore, electrophoretic impregnation was used for the modification of porous green bodies. Thus silica glasses with graded density and pore size as well as functionally graded composites were prepared.
C 2004 Kluwer Academic Publishers 1. Introduction Electrophoretic deposition (EPD) is a process known for decades [1], where charged particles move under the influence of a direct electric field towards an op￾positely charged electrode and coagulate there to form a stable deposit. Although EPD has been applied on an industrial scale for years as enamelling and lacquer￾ing technique (cataphoresis) [2, 3], it is not yet estab￾lished as a shaping process for functional ceramics and glasses. Among the ceramic coatings applied by EPD are e.g., phosphors [4], coatings for SOFCs [5], pho￾tovoltaic applications [6] or insulating layers [7]. In some cases even manufacturing on an industrial scale has become likely [8]. But in case of bulk ceramic or glass components no industrial manufacturing process has proved success￾ful so far. Nevertheless, several ceramic systems were investigated on a laboratory scale, including alumina [9], zirconia [10], SiC [11, 12] and PZT [13]. Compre￾hensive reviews about EPD as shaping technique for ceramics are given in [14, 15]. In all of these cases or￾ganic solvents were used as dispersant, which seems to be one of the problems why EPD has never established yet for large-scale production of ceramics. First of all, the deposition rates are significantly lower in compar￾ison with aqueous suspensions because of the much lower permittivity, thus very high electric field strengths have to be applied to achieve acceptable shaping times. Furthermore, severe safety precautions have to be met, if organic, often inflammable dispersants are used, es￾pecially in case of high voltages and/or high current densities. As a consequence the process cost increases. Finally, disposal of hazardous organic waste and treat￾ment of the suspensions for recovery of the dispersant as well as the absorption of volatile cracking products during heat treatment can prevent the introduction of an EPD facility into an existing production line. As an alternative aqueous suspensions can be used for the EPD of ceramics. Since only water is used as dispersant, no sophisticated safety precautions are nec￾essary and treatment of the suspensions after EPD is easy. Most important, very high deposition rates can be reached for comparably low applied electric field strengths [16]. Thus process times can be reduced to several seconds to minutes depending on the material used. Clay components with a thickness of 10 mm could be shaped from aqueous sanitary slips within 15 s [17]. But the only industrial attempt to produce tiles by EPD from aqueous suspensions [18] failed. The main problem associated with the use of aque￾ous suspensions for EPD, is the electrolysis-induced de￾composition of water above a DC voltage of about 1.4 V. The electrolysis results in a movement of ions towards the oppositely charged electrode, where recombination 0022–2461
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