Synthesis and microstructure control of nanocrystalline titania powders via a sol-gel process

Changes of structure and grain size in gel-derived nanocrystalline titania powders were monitored by X-ray diffraction and thermogravimetric experiments. The structural evolution of these powders can be significantly influenced by several preparation conditions. In comparison with the C5H8O2-catalyzed tirania gel, the HCl-catalyzed one crystallized into anatase at a much lower temperature, and the crystallite size is smaller after the same heat treatments. On the other hand, pure rutile phase can be more easily obtained in the C5H8O2-catalyzed gel. In the lower hydrolysis water content (r) samples, the grain size is smaller, and the starting temperature of the anatase-to-rutile (A --> R) transformation is a little lower, in comparison with those higher r-samples. A long period of aging at room temperature evidently enhances the A --> R transformation in the dry-gel powders. Several oxide additives can effectively prohibit the grain growth in these nanocrystalline powders. However, the effect of these additives on the A --> R transformation is quite different. (C) 1997 Elsevier Science S.A.