Binary Titania‐Silica Glasses Containing 10 to 20 Wt% TiO 2

A series of glasses in the TiO 2 ‐SiO 2 system was prepared by the flame hydrolysis boule process. Clear glasses containing as much as 16.5 wt% TiO 2 were obtained. More TiO 2 caused opacity due to phase separation and anatase/rutile crystallization during glass boule formation. Glasses in the 12 to ∼17 wt% TiO 2 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.