Non-isothermal Kinetic Analysis of Processes Occurring During Thermal Treatment of Kaolinite

A non-isothermal kinetic analysis of processes occurring during thermal treatment of kaolinite is carried out using differential thermal analysis on powder samples with heating rates from 1 to 10 degrees C min(-1) in static air atmosphere. For the parameterization of dehydroxylation process and crystallization of Al-Si spinel phase from metakaolinite the Kissinger method is used. The determined values of apparent activation energy for the dehydroxylation of kaolinite and formation of Al-Si spinel phase are (163 +/- 11) kJ mol(-1) and (826 +/- 16) kJ mol(-1), respectively. For the dehydroxylation of kaolinite the diffusion controlled growth of a new phase with a decreasing nucleation rate is determined as a mechanism of the process. The results also show that the formation of Al-Si spinel phase from metakaolinite is controlled by grain edge nucleation after saturation.