Dehydration kinetics of muscovite by in situ infrared microspectroscopy

Dehydration behavior of muscovite flake was investigated at 760-860A degrees C by using in situ high-temperature IR microspectroscopy for the OH absorption band around 3,620 cm(-1). Isothermal kinetic heating experiments at each temperature gave detailed decrease curves of the OH band area with time. These curves have been simulated by the first and second order reactions or mono- and two-dimensional diffusion processes. The mono-dimensional diffusion was found to give the best fit to the experimental data and apparent diffusion coefficients D were determined at 760-860A degrees C with the activation energy of 290 +/- A 20 kJ/mol. The apparent diffusion coefficients D varied with the sample thickness L. This variation can be explained by an m layers model with a unit length of L' with a constant diffusion coefficient D'. Therefore, the dehydration process might be rate-limited by mono-dimensional diffusion through tetrahedral silicate sheet perpendicular to (001) planes of muscovite with a unit length of L'.