Growth of rutile crystallites during the initial stage of anatase-to-rutile transformation in pure titania and in titania-alumina nanocomposites

An explanation based on the thermodynamics and kinetics of nucleation-growth type of transformations is discussed for the observed difference between the crystallite sizes of anatase and rutile phases during the initial stage of this transformation. Two situations are considered here, pure titania and titania phase in the titania-alumina nanocomposites. It is postulated that the critical nuclei size of rutile phase may be much larger than the transforming anatase particles.