Published online by Cambridge University Press: 17 March 2011
Quantitative thermal stability test of glass materials against crystallization is accelerated through a vertical temperature-gradient furnace. In the furnace, zinc tellurite glass melt is sucked into a 75cm-long glass capillary tube (ID 1.5 × OD 8 mmø) and the tube is kept inside to be annealed under a temperature gradient of 300~800°C/50cm. The time to precipitate is determined to make a set of T-T-T (Time-Temperature-Transform) diagrams for different composition and thermal hysteresis. Crystallization is not observed for 65TeO2-35ZnO and 70TeO2-30ZnO (mol%) super-cooled glass melt after 4000s annealing but their stability decreased if the melts were once quenched to below their glass transition temperature before the annealing.