Phase transformation in sol-gel titania containing silica

Titanium dioxide containing 5-10% silica has been prepared by the co-hydrolysis of titanium isopropoxide at pH 4 in presence of TEOS in different solvents such as methanol, ethanol and water. The resultant gels have been analyzed by BET surface area measurements and thermal analysis. Addition of 5% silica to TiO2 increases initial surface area of 89 to 188 m(2)/g. As the amount of silica is further increased to 10%, the surface area is further increased to 203 m(2)/g. The composition containing TiO2-10% SiO2 in ethanol medium achieved the highest specific surface area 232 m(2)/g while the corresponding sample in methanol had 217 m(2)/g. Addition of silica has further resulted in considerable increase of anatase-rutile transformation temperature > 800 degrees C. Addition of methanol and ethanol to titania-silica systems enhances the formation of rutile phase. This phase transformation has been followed by X-ray powder diffraction data and further, through impedance measurements on the precursor gel pellets heated to various temperatures and the latter has been presented as a very simple and convenient tool to study phase transformation in titania ceramics. (C) 1999 Elsevier Science B.V. All rights reserved.