Phase transformation of nanocrystalline anatase-to-rutile via combined interface and surface nucleation

The kinetics of phase transformation of nanocrystalline anatase samples was studied using x-ray diffraction at temperatures ranging from 600 to 1150 d egrees C. Kinetic data were analyzed with an interface nucleation model and a newly proposed kinetic model for combined interface and surface nucleati on. Results revealed that the activation energy of nucleation is size depen dent. In anatase samples with denser particle packing, rutile nucleates pri marily at interfaces between contacting anatase particles. In anatase sampl es with less dense particle packing, rutile nucleates at both interfaces an d free surfaces of anatase particles. The predominant nucleation mode may c hange from interface nucleation at low temperatures to surface nucleation a t intermediate temperatures and to bulk nucleation at very high temperature s. Alumina particles dispersed among the anatase particles can effectively reduce, the probability of interface nucleation at all temperatures.