Kinetics analysis of mullite formation reaction at high temperatures

A detailed kinetics analysis was performed on the mullite (3Al(2)O(3). 2SiO (2)) formation reaction occurring at high temperatures ranging from similar to 1600 to 1800 degrees C. The counterdiffusion model of Al3+ and Si4+ flu xes was used to derive the kinetics equation of the mullite formation react ion. From the parabolic kinetics between the thickness of the mullite layer and time, the reaction rate constant (k) for the mullite formation was det ermined to be a function of the average diffusion coefficient of Si4+ ions. This kinetics equation can be used to estimate the mullite formation at an y temperature. By substituting previous experimental data into the present kinetics equation, average diffusion coefficient values of Si4+ ions in the mullite layer were calculated and these values are in good agreement with the diffusion coefficient values calculated using Aksay's interdiffusion eq uation for mullite formation. The activation energy values for the diffusio n of the Si4+ ions were estimated to range from 730 to 780 kJ/mol, which ar e close to those obtained from previous diffusion and creep experiments. (C ) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.