LOW-TEMPERATURE NUCLEATION OF RUTILE OBSERVED BY RAMAN-SPECTROSCOPY DURING CRYSTALLIZATION OF TIO2

The thermal evolution of amorphous TiO2 powders, consisting of spherical particles and prepared by hydrolysis of a titanium ethoxide aerosol, was studied by using Raman spectroscopy. On calcination at 350-degrees-C, the solid crystallized, giving anatase as a major phase. A small amount of rutile was also detected and attributed to small seeds localized at the particle outlayer. The nucleation of rutile at so low a temperature was ascribed to the presence of organic impurities in the powders. The transformation of anatase into rutile was clearly observed after heating at 660-degrees-C.