Alev hidrolizi yöntemiyle sentezlenmiş, nano boyuttaki TiO2/SiO2 kompozitlerinin termal ve hidrotermal kararlılıkları

The phase stability of the flame hydrolytic synthesized TiO2/SiO2 nano-sized composites has been investigated under thermal and hydrothermal conditions. The pure titania (P25 Evonik Degussa) annealed under hydrothermal conditions (100 g/m3 absolute humidity, 600 oC) was found to have 85 % rutile fraction which was only 46 % when annealed at 600 oC without the introduction of humidity. The difference was attributed to the formation of oxygen vacancies under hydrothermal conditions possibly increasing the rate of transformation from anatase to rutile TiO2. Even the smallest amount of SiO2 doping was observed to retard the phase transformation and maintain the specific surface area after both thermal and hydrothermal treatments. The highest complete phase transformation temperature (1200 oC) and the maximum BET surface area at 1000 oC (57 m2/g) under H2O atmosphere, were both detected for 24.84 % silica content among TiO2/SiO2 composite series. The results obtained from different characterization methods; X-ray powder diffraction, Raman spectroscopy and BET surface area analysis are in good agreement with each other and support the discussed effects of H2O atmosphere and SiO2 doping.