Anatase-rutile phase transformation in the presence of Fe2O3 was investigated in air or Ar atmospheres by using X-ray diffraction and scanning electron microscopy techniques. Isothermal anatase-rutile transformation, as a function of time, was monitored between 825 and 950C. The data could be closely fitted by using various rate laws. In the presence of Fe2O3, the transition temperature was lowered and the transformation rate in air was increased. Transformation in the presence of Fe2O3, under an Ar atmosphere, was more rapid than it was in air. The enhancement effect of Fe2O3 was explained in terms of the formation of O vacancies. These were produced by Fe3+ diffusion in the TiO2 lattice. It was concluded that the enhancement effect was greater in an Ar ambient because Fe3+ diffusion in non-stoichiometric TiO2 was some 2 orders of magnitude faster than in stoichiometric TiO2.

Kinetics of the Anatase–Rutile Transformation in TiO2 in the Presence of Fe2O3. Gennari, F.C., Pasquevich, D.M.: Journal of Materials Science, 1998, 33[5], 1571-8