Electrophoretic deposition of silicon carbide

Electrophoretic deposition of silicon carbide (SiC) in ethyl alcohol was st udied using the simplest bath formulation allowing the production of accept able deposits. The object of the study was to explain the role of the diffe rent components in the bath, regarding both the dispersion of particles and the deposition mechanism. The elementary bath composition comprised SiC, e thyl alcohol, water, an aluminum salt, and a polymer chemically based on po ly(vinyl butyral (PVB), AlCl3 partly dissociated in the solution, depending on the water content, and absorbed strongly onto the SiC, Adsorption of al uminum species promoted the positive charge and the dispersability of the p articles, if some water was present. PVB did not adsorb onto SiC but decrea sed 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 AI(OH)(3), which reduced the surface charge and allow ed close contact between particles in the deposit. Excess water, above simi lar to 10 wt% of the solution, was harmful because it induced heavy hydroge n bubbling at the electrode and high bath conductivity. The diffusion of io nic species through the deposit controlled the electrolysis and deposition rates. Finally, a range of bath compositions for satisfactory deposition ra tes was established and explained.