Influence of size of dispersed silica particles on preparation of thick silica films by using electrophoretic sol-gel deposition

Monodispersed silica particles, which ranged from 0.14 to 0.42 mu m in diameter, were prepared by the sol-gel method. These particles were first separated from original sols, and dried, heat-treated, and then re-dispersed in a mixture of ethanol, water, and triethoxy(methyl)silane. Thick silica films without micro-cracks were formed by electrophoretic deposition of the particles on a stainless steel sheet in the re-dispersed sols. The weight of the silica films deposited was increased with increasing particle size at a given applied voltage. On the other hand, density of the films was increased with decreasing particle size. When the particle size was 0.32 mu m in diameter, crack-free films of ca. 20 mu m in thickness were prepared after heat treatment at 800 degrees C for 1 h.