Kinetics and mechanism of dehydration of kaolinite, muscovite and talc analyzed thermogravimetrically by the third-law method

• Published in: Journal of Thermal Analysis and Calorimetry 2005-09, Vol.82 (1), p.15-22
• Main Authors: L'VOV, B. V, UGOLKOV, V. L
• Format: Article
• Language: English
• ISSN: 1388-6150; 1588-2926; 1572-8943; 0368-4466
• DOI: 10.1007/s10973-005-0886-0

The third-law method has been applied to determine the enthalpies, DeltarHT, for dehydration reactions of kaolinite, muscovite and talc. The DeltarHTvalues measured in the equimolar (in high vacuum) and isobaric (in the presence of water vapour) modes (980+/-15, 3710+/-39 and 2793+/-34 kJ mol, for kaolinite, muscovite and talc, respectively) practically coincide if to take into account the strong self-cooling effect in vacuum. This fact strongly supports the mechanism of dissociative evaporation of these compounds in accordance with the reactions (primary stages): Al2O3*2SiO2*2H2O(s)- > Al2O3(g){downwards arrow}+2SiO2(g){downwards arrow}+2H2O(g); K2O*3Al2O3*6SiO2*2H2O(s) - > K2O(g){downwards arrow}+3Al2O3(g){downwards arrow}+6SiO2(g){downwards arrow}+2H2O(g) and 3MgO*4SiO2*H2O(s) - > 3MgO(g){downwards arrow}+4SiO2(g){downwards arrow}+H2O(g). The values of the Eparameter deduced from these data for equimolar and isobaric modes of dehydration are as follows: 196 and 327 kJ molfor kaolinite, 309 and 371 kJ molfor muscovite and 349 and 399 kJ molfor talc. These values are in agreement with quite a few early results reported in the literature in 1960s.