Effects of negative ions in aqueous Ti solution on formation of ultrafine TiO2 powder by low temperature homogeneous precipitation

Ultrafine crystalline TiO2 powder was prepared by homogeneous precipitation by heating aqueous TiOCl2 solution below 70degreesC. The TiO2 powder was formed even at room temperature. By spontaneous hydrolysis of the aqueous TiOCl2 solution, all the precipitates were completely crystallized in the rutile phase. These, however, were transformed into the anatase phase by adding more TiOSO4 solution to the aqueous TiOCl2 solution. The formed secondary particles consisted of needle-shaped, spherical and mixed primary particles corresponding to the rutile, anatase and mixed phases, respectively. It seems that the formation and phase determination of crystalline TiO2 powder during the precipitation may be affected by capillary pressure. This pressure probably depends on the shape of the primary particles.