Effect of Vapor Pressure of H 2 O on the Formation of Nano-Crystalline TiO 2 Ultrafine Powders

Mono-dispersed TiO 2 ultrafme particles with diameters 40-400nm were obtained from aqueous TiOCl 2 solution with 0.67M Ti 4+ concentration prepared diluting TiCl 4 by homogeneous precipitation process in the ranges of 17-230°C. With the spontaneous hydrolysis of TiOCl 2 , which means the natural decrease of pH value in the aqueous solution, all mono-dispersed precipitates were crystallized with the anatase or rutile TiO 2 phase. TiO 2 precipitate with the pure rutile phase was fully formed at the temperatures below 65 °C, not involving the evaporation of H 2 O, and above 155 °C, which were available by suppressing it. TiO 2 precipitate with rutile phase including a small amount of the anatase phase started to be formed in the intermediate temperatures above 70 °C showing the full formation of the anatase above 95 °C under the free evaporation of H 2 O. However, in the case of completely suppressing H 2 O evaporation at the temperatures above 70°C, TiO 2 precipitate with anatase phase was fully transformed into the precipitate with the rutile phase by the vapor pressure of H 2 O. Therefore, the formation of TiO 2 precipitates with the rutile phase around room temperature would be caused due to the existence of the capillary pressure between the agglomerated needle-shaped particles or the ultrafme clusters, together with the slow reaction rate.