The kinetics of Al–Si spinel phase crystallization from calcined kaolin

The crystallization of Al–Si spinel from medium ordered kaolin with high content of kaolinite was investigated using the differential thermal analysis (DTA). The apparent activation energy of the process was evaluated from the dependence of exothermic peak of crystallization on heating rate. Within the applied interval of heating rate (1–40 K min−1) the temperature of peak maximum increases from initial value of 1220.5 K in about 54.2 K. The apparent activation energy of the process 856±2 kJ mol−1was calculated using the Kissinger equation. The growth morphology of Al–Si spinel crystal was evaluated from the Avrami parameter. The average value of morphology parameter determined within the observed interval of heating rate is 3.08±0.03. This value indicates that crystallization mechanism of Al–Si spinel phase proceeds by bulk nucleation of the new phase with constant number of nuclei and that the three-dimensional growth of crystals is controlled by the reaction rate on the phases interface.