Heat Treatment and Particle Grain Size Effect on the TiO2 Nanoparticle Phase Alteration

TiO2 has drawn much research attention in recent years because of possible applications to environmental purification, selfclean surface and solar energy converters. Anatase and rutile are the two major crystal phases of TiO2. Heat treatment can changecrystal structure and physical properties of TiO2 nanoparticles. In this work, the effect of particles size on anatase-rutile phase transformation due to heat treatment process has been studied. We have used powders with two different sizes with average sizesof 30 nm named as A and 70 nm named as B. The powders were annealed at 400, 500, 600, 700, 800, 900 and 1000°C for 2 h under ambient atmosphere and then cooled slowly. The titania powders obtained have been characterized using transmissionelectron microscopy (TEM), X-ray diffraction (XRD) and BET method. Grain size of samples and morphologic changes after heat treatment were observed by TEM, also particle size effect on the anatase-rutile phase transformation for A and B powders wereinvestigated by XRD technique. Phase transitions from anatase to rutile for powder A occurs at the lower temperature compared to powder B, that is probably due to difference of coarsening mechanism grain size for powder A and B.