Preparation of uniform colloidal dispersions by chemical reactions in aerosols. I. Spherical particles of titanium dioxide

Abstract

Spherical titanium dioxide particles were prepared by hydrolysis of aerosols consisting of liquid titanium(IV) compounds. The droplets of the latter were nucleated with AgCl in a falling film generator and subsequently hydrolyzed in specially designed chambers kept at different temperatures. When titanium(IV) ethoxide was used as starting material, TiO 2 spheres of narrow size distribution were obtained with modal diameters ranging between 0.06 and 0.6 μm. The size of the particles could be altered by changing the temperature of the falling film generator, the flow rate of the carrier gas, and the AgCl nuclei concentration. The titanium dioxide particles so prepared were essentially amorphous. Titanium tetrachloride was also used as the liquid aerosol material. Owing to the vapor pressure characteristics of this compound, much higher concentration of the droplets was obtained in the same equipment. However, the titanium dioxide powder, resulting from the hydrolysis of TiCl 4 aerosols, consisted of spheres of broader size distributions. The crystallinity of the solid particles could be changed by heating of the solid aerosol stream at different temperatures. The titanium dioxide powders, prepared by the aerosol technique, could be readily dispersed in water. The particle charge was pH dependent and showed an electrophoretic isoelectric point between pH 4.5 and 5.5.