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

The kinetics of mullite crystallization from Al2O3-SiO2 glasses with chemic al compositions ranging from 15 to 50 mol% Al2O3 were investigated under no n-isothermal conditions using DTA. The glasses were prepared by ultra-quenc hing 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 degreesC associated with mu llitization. This crystallization temperature increased slightly with decre asing Al2O3 content. The exothermic peak split into two peaks at a glass co mposition of about 25 mol% Al2O3. This splitting is thought to be related t o phase separation of the glass preceding mullitization. The activation ene rgies for the nucleation-growth mechanism of mullitization, calculated by t he Kissinger method, were 900-1300 kJ/mol, in good agreement with those for glass fibers obtained under isothermal conditions. (C) 2001 Elsevier Scien ce Ltd. All rights reserved.