PREPARATION OF UNIFORM COLLOIDAL DISPERSIONS BY CHEMICAL-REACTIONS INAEROSOLS .6. SILICA TITANIA COMPOSITE-PARTICLES

Spherical silica/titania particles were prepared by nebulizing with a nozzle liquid mixtures of tetraethyl orthosilicate (TEOS) and titanium (IV) ethoxide [Ti(OEt)4] and contacting the resulting droplets with wa ter vapor. The size distribution of the liquid aerosols was improved b y mechanically eliminating the larger droplets and by the evaporation and condensation of the remaining droplets in the presence of AgCl nuc lei introduced with the carrier gas. The composition of the resulting solids differed from that expected from the original liquids. Furtherm ore, the particles were not internally homogeneous; the surface layers contained a higher molar ratio of titania than the bulk. The electrok inetic data corroborated the surface composition. On calcination at 70 0-degrees-C, the titania component crystallized to anatase in the orig inally amorphous particles.