EMULSION SYNTHESIS OF SPHERICAL TIO2-SIO2 COLLOIDS FROM METAL ALKOXIDES

A method for synthetizing spherical, submicron titania-silica powders from an oil/water emulsion of metal alkoxides has been developed. The emulsions are formed spontaneously, without the aid of surfactants or other liquids usually associated with emulsion processes. The process capitalizes on immiscibility in the metal alkoxide-water-alcohol ternary system. Control of the hydrophobic nature of partially hydrolized metal alkoxides, minimization of γo/w and a large ethanol concentration difference between the metal alkoxide solution and the aqueous phase during mixing results in spontaneous emulsification of the metal alkoxide in water. Calculations of the hydrophilic-lipophilic balance number are used successfully to predict metal alkoxide emulsion formation. For the TiO2SiO2 system, ammonium hydroxide in the aqueous phase stabilizes the emulsion against coalescence by catalyzing the gelation of the metal alkoxide droplets to porous metal oxide particles. Powders can be synthesized with a high surface area and average particle sizes ranging from 0.05 μm to as large as 1.0 mm diameter. © 1990.