Studies on Cataphoretic Deposition of Alumina

Abstract

The influences of solvents and electrolytes on the yield, electrical conductivity, strength and eccentricity in the cataphoretic deposition of alumina were investigated. The cataphoretic suspension was composed of alumina powder, electrolytes, alcohol and water. The deposition was made by applying ground potential on the coating electrode and positive potential on the opposite electrode.The results are summarized as follows:(1) Hamaker's formula on cataphoretic deposition holds good even in the case in which electrolytes are added to the cataphoretic suspension.(2) Addition of water to the cataphoretic suspension containing alcohol as solvent increased the cataphoretic yield and electrical conductivity. The suspension containing 50%/50% alcohol-water gave good yield and presented smooth deposition surface.(3) The addition of nitrates saw better cataphoretic deposition than the addition of sulfate and acetate. Especially, the addition of aluminium nitrate (Basic) in combination with magnesium nitrate saw most stable and effective deposition.(4) Aluminium nitrate (Basic) increased hardness of alumina deposition after sintering, and decreased its ductility, while magnesium nitrate, on the contrary, decreased its hardness and increased its ductility. Their combination is therefore recommended.(5) The eccentricity of alumina deposition on coil decreased as the electrical conductivity of suspension increased.