Crystallization of baria-titania-silica glasses

The critical cooling rate for glass formation, Rc, and the crystallization kinetics of the compositions (1/2)(100-x)BaO-(1/2)(100-x)TiO2-(x)SiO2 with x = 20, 25, 30, 33.3, and 40 mol pct were studied using a thermal image furnace. Crystallization was studied under nonisothermal conditions, and the data were analyzed using the Johnson-Mehl-Avrami equation. The Rc and activation energy for crystallization both decrease with increasing silica content. Fresnoite, Ba2TiSi2O8, crystallized from all of the glasses when they were reheated. The infrared absorption spectra of the glasses and crystals show that they both contain (Si2O7) and square pyramidal (TiO5) groups.