Electrophoretic Deposition of Silicon Carbide

Abstract

Electrophoretic deposition of silicon carbide (SiC) in ethyl alcohol was studied using the simplest bath formulation allowing the production of acceptable deposits. The object of the study was to explain the role of the different components in the bath, regarding both the dispersion of particles and the deposition mechanism. The elementary bath composition comprised SiC, ethyl alcohol, water, an aluminum salt, and a polymer chemically based on poly(vinyl butyral (PVB). AlCl3 partly dissociated in the solution, depending on the water content, and absorbed strongly onto the SiC. Adsorption of aluminum species promoted the positive charge and the dispersability of the particles, if some water was present. PVB did not adsorb onto SiC but decreased the sedimentation rate. Particle deposition was bound to the occurrence of an electrolytic reaction. That reaction combined the reduction of water and the formation of Al(OH)3, which reduced the surface charge and allowed close contact between particles in the deposit. Excess water, above ∼10 wt% of the solution, was harmful because it induced heavy hydrogen bubbling at the electrode and high bath conductivity. The diffusion of ionic species through the deposit controlled the electrolysis and deposition rates. Finally, a range of bath compositions for satisfactory deposition rates was established and explained.