Dense, bubble-free ceramic deposits from aqueous suspensions by electrophoretic deposition
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Dense, bubble-free ceramic deposits from aqueous suspensions by electrophoretic deposition Tetsuo Uchikoshi, Kiyoshi Ozawa, Benjamin D. Hatton,a) and Yoshio Sakka National Research Institute for Metals, 1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, Japan (Received 7 August 2000; accepted 8 September 2000)
The characteristics of electrophoretic deposition (EPD) of positively charged particles onto a cathode were investigated using aqueous alumina and zirconia suspensions. The deposition was performed using several kinds of metal substrates at different current densities. For most substrate materials, a large number of macropores appeared in the deposit, and their size increased with the current density due to gas bubble formation. However, no macropores were formed in the deposit on a palladium substrate, regardless of the current density. The green density and sintering properties of the EPD deposits on a palladium substrate from aqueous suspensions were the same as from slip casting. Bubble-free zirconia/alumina laminate composites were also fabricated by EPD from aqueous suspensions. Electrophoretic deposition (EPD) is a colloidal processing technique for ceramics.1 It has been employed to fabricate thin films, multilayered composites, functionally graded materials, etc.2 Nonaqueous suspensions are usually preferred for EPD to avoid the electrolysis of the solvent and obtain a bubble-free deposit.1,2 However, an aqueous system has the advantages of low-cost processing, lower electrical potential requirement, and lower environmental cost. Some trials have been conducted for the fabrication of a bubble-free deposit from an aqueous suspension. The simplest method is to reduce the applied voltage lower than the decomposition voltage of water (1.23 V at 25 °C),3 but the deposition rate is too low and it is not practical. Ryan et al.4,5 used porous molds so the generated gas would pass through the mold and reduce the gas trapped in the deposit. Clasen6 suppressed bubble formation by depositing on a microporous membrane placed in front of an electrode. Other studies involved using negatively charged particles for the absorption of generated oxygen gas by an easily oxidizable anode like Zn.7–10 In this case, metal cations of the substrate easily came out and contaminated the deposit. In this study, the EPD characteristics of positively charged particles onto various cathodic substrates were investigated using an aqueous alumina suspension. Fabrication of zirconia/ alumina laminate composites was also attempted by EPD from zirconia and alumina aqueous suspensions.
a)
Present address: Department of Metallurgy and Materials Science, University of Toronto, Room 140, 184 College Street, Toronto, Ontario, Canada M5S 3E4 J. Mater. Res., Vol. 16, No. 2, Feb 2001
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Alumina (Sumitomo Chem. Co. Ltd., Tokyo, Japan, AKP-50, average particle size of 0.20 m) and zirconia (Tosoh Corp., Tokyo, Japan, TZ-3Y, 60 nm) powders were dispersed at pH 4 in distilled water by ultrasound, and aq
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