Effect of Vapor Pressure of H2O on the Formation of Nano-Crystalline TiO2 Ultrafine Powders

Abstract

ABSTRACTMono-dispersed TiO2 ultrafme particles with diameters 40-400nm were obtained from aqueous TiOCl2 solution with 0.67M Ti4+ concentration prepared diluting TiCl4 by homogeneous precipitation process in the ranges of 17-230°C. With the spontaneous hydrolysis of TiOCl2, which means the natural decrease of pH value in the aqueous solution, all mono-dispersed precipitates were crystallized with the anatase or rutile TiO2 phase. TiO2 precipitate with the pure rutile phase was fully formed at the temperatures below 65 °C, not involving the evaporation of H2O, and above 155 °C, which were available by suppressing it. TiO2 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 H2O. However, in the case of completely suppressing H2O evaporation at the temperatures above 70°C, TiO2 precipitate with anatase phase was fully transformed into the precipitate with the rutile phase by the vapor pressure of H2O. Therefore, the formation of TiO2 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.