PREPARATION OF TIO2-SIO2 GLASS VIA SOL-GEL PROCESS CONTAINING A LARGE AMOUNT OF CHLORINE

Transparent and colorless TiO2-SiO2 glasses containing as much as 15 wt% TiO2 were prepared via a sol-gel process of titanium and silicon alkoxides in the presence of a large amount of chlorine in the form of titanium tetrachloride. The homogeneity of the gel, evaluated by means of Fourier transform infrared spectrometry and X-ray diffractometry, improved as the amount of titanium tetrachloride increased and no crystallinity of the heat-treated gel (similar to 1000 degrees C) was observed when the Cl/Ti ratio exceeded 1.2. A defect-free and transparent TiO2 (15 wt%)-SiO2 glass plate, 25 mm in diameter and 3 mm thick, was obtained by employing propylene carbonate as a drying chemical control agent and heat-treated at 1000 degrees C. A very low thermal expansion coefficient, - 0.61 x 10(-7)/degrees C, was observed for a 6.93 wt% TiO2 glass. Densities of the glasses were 2.2-2.3.