Binary Titania-Silica Glasses Containing 10 to 20 Wt% TiO2

A series of glasses in the TiO₂-SiO₂ system was prepared by the flame hydrolysis boule process. Clear glasses containing as much as 16.5 wt% TiO₂ were obtained. More TiO₂ caused opacity due to phase separation and anatase/rutile crystallization during glass boule formation. Glasses in the 12 to ∼17 wt% TiO₂ range were metastable and showed structural rearrangements on heat treatment at temperatures as low as 750CEC (∼200° below the annealing point). These changes were accompanied by large changes in thermal expansion. Thermal treatment can be designed to produce almost any desired expansion between α_-200+700=−5 × 10^-7/°C and +10 × 10^-7/°C. Zero expansion between 0 and 550°C was obtained. Evidence that these changes are due to phase separation and anatase formation is presented. Viscosity data in the glass transition range, refractive index, and density are also presented.