Kaolinite thermal decomposition

Figure 4.8. Changes in the Si spectra of kaolinite during its thermal decomposition, showing the progressive formation of the broad metakaolinite resonance envelope - 99 to - 102 ppm) at 650-800°C, the sudden appearance of free Si02 (—110 ppm) at 970°C, and the formation of mullite (— 88 to — 92 ppm) above 1100°C. Adapted from Mackenzie et al. (1985a) by permission...

Figure 5.30. Changes in the Al site occupancy of kaolinite during its thermal decomposition, after Temuujin et al. (1998a) by permission of the copyright owner.

Kaolinite is transformed into X-ray amorphous state when activated in air. According to authors [14,15], amorphization involves the destruction of bonds between tetrahedral and octahedral layers inside the package, till the decomposition into amorphous aluminium and silicon oxides. Other researchers [ 16,17] consider that amorphized kaolinite conserves the initial ordering of the positions of silicon atoms while disordering of the structure is due to the rupture of A1 - OH, Si - O - A1 bonds and the formation of molecular water. Endothermic effect of the dehydration of activated kaolinite is shifted to lower temperatures while intensive exo-effect with a maximum at 980°C still conserves. When mechanically activated kaolinite annealed at 1(X)0°C, only mullite (3Al20j-2Si0j) and X-ray amorphous SiOj are observed. In this case, the phase with spinel structure which is formed under thermal treatment of non-activated kaolinite is not observed thus, mechanical activation leads to the formation of other phases. 

Zhang, Y., Liu, Q., Xiang, J., Frost R.L. Thermal stability and decomposition kinetics of styrene-butadiene mbber nanocomposites filled with different particles sized kaolinites. Appl. Clay Sci. 95, 159-166 (2014)... 

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