Effect of hydrothermal treatment of amorphous titania on the phase change from anatase to rutile during calcination

Hydrothermal treatment of amorphous titania has been used to crystallize an d stabilize the anatase phase of titania. The hydrothermal treatment condit ions can be used to control the physical properties of the crystallized ana tase powder, which in turn control the subsequent phase-change properties o f the anatase/rutile phase change. The synthesis history of the amorphous s tarting material is crucial in determining the final phase-change character istics. The presence of a small amount of brookite phase contamination in t he anatase, results in rapid conversion to rutile. Crystallite size also pl ays an important role in determining the anatase stability, with increasing crystallite size resulting in higher stability, but the phase-change tempe rature was shown to have only a weak dependence on surface area.