Non-isothermal kinetic analysis of illite dehydroxylation

A non-isothermal kinetics of the two-step dehydroxylation of illite is carried out using thermogravimetric analysis. The experiments are performed on powder samples with heating rates from 1 °C min–1 to 10 °C min–1 in a dynamic atmosphere of dry air. From these measurements, the values of apparent activation energy are calculated by the Kissinger method. The calculated values of Ea for the first and second step of illite dehydroxylation are (195 ± 16) kJ mol−1 and (354 ± 25) kJ mol–1, respectively. The results also show that the trans-vacant layer dehydroxylation is controlled by one-dimensional diffusion with an instantaneous nucleation rate. For the cis-vacant layer dehydroxylation, the results indicate two possible dominant mechanisms: 2D diffusion controlled process and 1D phase boundary controlled reaction if the instantaneous nucleation is assumed.