Homogeneous Precipitation of TiO ₂ Ultrafine Powders from Aqueous TiOCl ₂ Solution

Crystalline TiO 2 powders were prepared by the homogeneous precipitation method simply by heating and stirring an aqueous TiOCl 2 solution with a Ti 4+ concentration of 0.5 M at room temperature to 100°C under a pressure of 1 atm. TiO 2 precipitates with pure rutile phase having spherical shapes 200‐400 nm in diameter formed between room temperature and 65°C, whereas TiO 2 precipitates with anatase phase started to form at temperatures >65°C. Precipitates with pure anatase phase having irregular shapes 2‐5 µm in size formed at 100°C. Possibly because of the crystallization of an unstable intermediate product, TiO(OH) 2 , to TiO 2 x H 2 O during precipitation, crystalline and ultrafine TiO 2 precipitates were formed in aqueous TiOCl 2 solution without hydrolyzing directly to Ti(OH) 4 . Also, formation of a stable TiO 2 rutile phase between room temperature and 65°C was likely to occur slowly under these conditions, although TiO 2 with rutile phase formed thermodynamically at higher temperatures.