Elucidation of electrophoretic deposition behavior of particles suspended in aqueous media and characterization of highly structure-ordered ceramics

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Electrophoretic deposition characteristics of ceramic aqueous suspensions were studied using palladium electrodes to suppress the hydrogen bubble generation at a cathode which disturbed the electrophoresis of the particles and suppress their deposition. The apparent transport number of the surface-charged particles was very low and they were not dominant carrier species in the solvent. In the EPD at a constant current mode, applied voltage between the electrodes varied with the pH of the solvent or the ion conductivity. Lower pH gave lower deposition rate but higher particle packing.Mechanical and electrical properties of the zirconia/alumina laminate composites fabricated by EPD from aqueous suspensions were characterized. Crack deflection within the alumina layers of the laminate composites was observed because of high compressive residual stress in the alumina layers. The 3Y TZP/alumina laminate composite showed the electrical properties of 3Y-TZP in the parallel direction to the alumina layers and those of alumina in the perpendicular direction. Electrical conductivity measurement well reflected the laminar structure of the laminate composite. It was demonstrated that EPD was well suited to produce layered composites with strongly bonded interfaces.The fabrication of crystalline-textured alumina ceramics were also attempted by EPD in a strong magnetic field using a deflocculated suspension of single crystalline alumina particles. The crystalline orientation in the textured ceramics could be controlled by varying the angle between the vectors B and E (ψ B-E) during EPD. Average orientation angle estimated from the XRD data was fairly consistent with the angle ψ B-E. The cross sectional microstructures of the laminate composites clearly showed the changes in crystalline texture at the interfaces between the layers. It was demonstrated that the EPD in a strong magnetic field was a promising processing technique for making crystalline textured ceramics.