Crystallization kinetics of mullite from Al₂O₃-SiO₂ glasses under non-isothermal conditions

The kinetics of mullite crystallization from Al₂O₃-SiO₂ glasses with chemical compositions ranging from 15 to 50 mol% Al₂O₃ were investigated under non-isothermal conditions using DTA. The glasses were prepared by ultra-quenching of molten droplets formed at the tip of a sintered aluminosilicate rod by an infra-red imaging furnace quenched by a twin-roller system. All the samples showed an exothermic peak at about 1000°C associated with mullitization. This crystallization temperature increased slightly with decreasing Al₂O₃ content. The exothermic peak split into two peaks at a glass composition of about 25 mol% Al₂O₃. This splitting is thought to be related to phase separation of the glass preceding mullitization. The activation energies for the nucleation-growth mechanism of mullitization, calculated by the Kissinger method, were 900-1300 kJ/mol, in good agreement with those for glass fibers obtained under isothermal conditions (Takei, T., Kameshima, Y., Yasumori, A. and Okada, K., Crystallization kinetics of mullite in alumina-silica glass fibers. J. Am. Ceram. Soc., 1999, 82, 2876-2880).