PRECIPITATION OF SILICA ON TITANIUM-DIOXIDE SURFACES .1. PREPARATION OF COATED SURFACES AND EXAMINATION BY ELECTROPHORESIS

Silica was precipitated at 90°C from sodium silicate solutions onto the surface of pure rutile and a commercial rutile, and the resultant products were examined by electrophoresis. Similar results were obtained for the two oxides. Surface silica concentrations of >2.5% gave products exhibiting isoelectric points characteristic of silica but to obtain reversible mobility/pH curves not showing solubility of the coating at low pH required ∼5%. The precipitation behavior is interpreted in terms of the solubility diagram for silica. At low surface concentration the silica is adsorbed in the monomeric form; at high concentrations polymerization occurs at the surface producing a coherent layer. © 1979.