Heat-stimulated crystallization and phase transformation of titania nanoparticles

Abstract To better understand the fundamental aspects of nanoparticle formation and transformation in the TiO2-H2O system the amorphous titania was synthesized as a precursor to studying crystal genesis, evolution, and transformation under heat treatment in air. The necessary depth of study was provided by comprehensive analysis using methods of PXRD, HT-PXRD, DSC-TG, TEM, BET adsorption, and helium pycnometry. The smallest crystallite size of the anatase phase is shown to be defined by the size of the initial amorphous titania nanoparticles. The amorphous state of initial titania nanoparticles is stabilized by water molecules incorporated into their structure. The anatase-to-rutile phase transition occurs when the average crystallite size of the anatase reaches the value of 35-45 nm. An explanation for a drastic change of the average crystallite size during the anatase-to-rutile transition repeatedly found in researches is in the difference in shapes of curves of crystallite size distribution.