SILICA COATING AT THE NANOMETER LEVEL ON AN ALPHA-ALUMINA FINE POWDER

Alumina fine powder which adsorbed a given amount of water was dispers ed in a hydrophobic solution of n-hexane and ethyl silicate with a sma ll amount of surfactant such as fatty acid, alkyl amine or sorbitan mo nostearate (Span 60). Ultra-fine particles and a thin film of silica w ere formed on the alumina particles after being coated in the solution with stearic acid and stearylamine, respectively. The addition of Spa n 60 reduced the catalytic activity of stearic acid and stearylamine f or the hydrolysis. The silica content of the powder after coating trea tment in the presence of stearylamine was nearly equal to that calcula ted from the amount of water adsorbed on the alumina powder. This sili ca content was controllable up to 15 wt.% by adjusting the amount of a dsorbed water.