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Abstract: Thermogravimetric analysis–mass spectrometry, X-ray diffraction and scanning electron microscopy (SEM) were used to characterize eight kaolinite samples from China. The results show that the thermal decomposition occurs in three main steps (a) desorption of water below 100°C, (b) dehydration at about 225°C and (c) well defined dehydroxylation at around 450°C. It is also found that decarbonization took place at 710°C due to the decomposition of calcite impurity in kaolin. The temperature of dehydroxylation of kaolinite is found to be influenced by the degree of disorder of the kaolinite structure and the gases evolved in the decomposition process can be various because of the different amount and kinds of impurities. It is evident by the mass-spectra that the interlayer carbonate from impurity of calcite and organic carbon is released as CO2 around 225, 350 and 710°C in the kaolinite samples. [ABSTRACT FROM AUTHOR]

Abstract: Two kinds of coal-bearing kaolinite from China were analysed by X-ray diffraction (XRD), Thermogravimetric analysis–mass spectrometry (TG–MS), infrared emission spectroscopy. Thermal decomposition occurs in a series of steps attributed to (a) desorption of water at 68°C for Datong coal-bearing strata kaolinite and 56°C for Xiaoxian with mass losses of 0.36% and 0.51%, (b) decarbonization at 456°C for Datong coal-bearing strata kaolinite and 431°C for Xiaoxian kaolinite, (c) dehydroxylation takes place in two steps at 589 and 633°C for Datong coal-bearing strata kaolinite and at 507 and 579°C for Xiaoxian kaolinite. This mineral was further characterised by infrared emission spectroscopy (IES). Well-defined hydroxyl stretching bands at around 3695, 3679, 3652 and 3625cm−1 are observed. At 650°C all intensity in these bands is lost in harmony with the thermal analysis results. Characteristic functional groups from coal are observed at 1918, 1724 and 1459cm−1. The intensity of these bands decrease by thermal treatment and is lost by 700°C. [ABSTRACT FROM AUTHOR]