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).