Effect of HCl concentration and reaction time on the change in the crystalline state of TiO2 prepared from aqueous TiCl4 solution by precipitation

TiO2 powder with 50% by volume or more of brookite phase was obtained by heating aqueous TiCl4 solution, whose final concentration of HCl after reaction was kept between 4.9 and 6.4 M, at 80 °C for 15 h. Rutile-type TiO2 was obtained at 5 h of reaction time, a mixture of predominant brookite and rutile at 10–15 h while rutile phase was formed at 25 h. Brookite phase was transformed directly to rutile phase with increase of reaction time but to rutile via anatase phase through heat treatment.