AN EMULSION METHOD FOR PRODUCING FINE, LOW-DENSITY, HIGH-SURFACE-AREASILICA POWDER FROM ALKOXIDES

Fine silica powders were prepared by the hydrolysis and condensation o f an emulsion of tetraethyl orthosilicate (TEOS) droplets in a continu ous water phase. No additions of alcohol, as a mutual solvent for the TEOS and water, or of strong acid or base catalysts, as required in th e more conventional set-gel methods, were used. The emulsion was produ ced by mechanical mixing and was stabilized against separating out of the phases by increasing the viscosity of the water with a commercial thickening agent, Texipol. The TEOS/water emulsion reacted to form int o a loose particulate gel, which could be crushed to a powder after dr ying at 40 degrees C. The amorphous silica powders produced had low ta pping densities (approximately 0.2 g cm(-3)), small particle sizes ( < 30 nm) and high specific surface areas (50-400 m(2) g(-1)).