Kinetic Analysis of Illite Dehydroxylation Based on Differential Scanning Calorimetry

The two-step dehydroxylation of illite is studied using the differential scanning calorimetry on powder samples with heating rates from 1 to 10 ${\deg}$C min$^{-1}$ in a dynamic argon atmosphere. The values of apparent activation energy and pre-exponential factor are calculated using the Kissinger method. The determined values of apparent activation energy and pre-exponential factor of trans-vacant layer dehydroxylation are $(227 \pm 6)$ kJ mol$^{-1}$ and $(2.87 \pm 0.09) \times 10^{13}$ min$^{-1}$, respectively. The results also show that this process can be characterized by 1D diffusion controlled reaction with instantaneous nucleation rate. For the cis-vacant layer dehydroxylation, the values of apparent activation energy and pre-exponential factor are $(242 \pm 10)$ kJ mol$^{-1}$ and $(5.37 \pm 0.23) \times 10^{12}$ min$^{-1}$, respectively. The value of Avrami peak factor for this step indicates diffusion controlled growth of the new phase with zero or decreasing nucleation rate.