Preparation of Uniform Colloidal Dispersions by Chemical Reactions in Aerosols. VI. Silica/Titania Composite Particles

Spherical silica/titania particles were prepared by nebulizing with a nozzle liquid mixtures of tetraethyl orthosilicate (TEOS) and titanium(rv) ethoxide [Tj(OEtl4 ] and contacting the resulting droplets with water vapor. The size distribution of the liquid aerosols was improved by mechanically eliminating the larger droplets and by the evaporation and condensation of the remaining droplets in the presence of AgCI nuclei introduced with the carrier gas. The composition of the resulting solids differed from that expected from the original liquids. Furthermore, the particles were not internally homogeneous; the surface layers contained a higher molar ratio of titania than the bulk. The electrokinetic data corroborated the surface composition. On calcination at 700°C, the titania component crystallized to anatase in the originally amorphous particles.