The kinetics of dehydroxylation of kaolinite.

The dehydroxylation of kaolinite has been investigated by isothermal thermogravimetry. Kinetic analysis using the Avrami equation shows that a combination of atomic mechanisms operates throughout the T range 743 K to 890 K. An empirical activation energy of 222 kJ/mol was calculated from the Arrhenius relationship using rate constants based on diffusion and homogeneous models. The activation energy (E_a) was calculated for a series of degrees of dehydroxylation by the time to a given fraction method, showing an increase in E_a during the early stages of the reaction. The isothermal plots indicate that OH is retained in the final stages of the reaction. The observations are explained in terms of a reaction mechanism in which kaolinite grains dehydroxylate from the edges upwards, parallel (001). (Author's abstract)-D.J.M.