Effect of thermal history on the phase separation and crystallization of some ROAl 2O 3SiO 2 glasses

Abstract

Two glasses were selected, one with the base composition close to that of cordierite (11% TiO 2 was added) and another glass with the composition of SiO 2 60%, Al 2O 3 15%, ZnO 25% (mol%) (4% ZrO 2 was added). The effects of phase separation on the behavior of crystallization of these two glasses with different thermal histories (water and air quenching from glass melt or pre-annealed at 650°C/10 h, 750°C/10 h, and 75°C/ 100 h) were investigated by using DTA, X-ray diffraction analysis and SEM. Activation energy of crystal growth was also determined. From the experimental results the following conclusions are drawn: (1) dispersed spheroidal liquid droplet phases are found in both glasses of different compositions prepared by melt quenching. These dispersed phase droplets will aggregate and grow as the pre-annealing temperature rises and the soaking time increases. (2) Phase separation can be altered for glass of same composition by varying the thermal history, which influences the type of primary crystalline phase and crystalline phase transformation process, but the final crystalline phase is not affected. (3) The activation energy of crystal growth is determined by the structures of the primary crystalline phases for both glasses of different thermal history.