Thermodynamics of the Various High Temperature Transformations of Kaolinite

N. C. Schieltz* and M. R. Soliman
* Colorado School of Mines, Golden, Colorado.
Ministry of Industry, Geological Survey and Mineral Research Department, Cairo, Egypt.

Abstract: Thermodynamic calculations of ΔG for all possible transformations of metakaolin at the temperature of the first DTA exothermic peak indicates that the most stable transformation is the one that yields mullite rather than γ-alumina.

The energy of crystallization of γ-alumina is quite small—36,513 cal per mol, compared with the energy of crystallization of mullite—336,180 cal per mol. Furthermore, the crystallization of γ-alumina is very slow, and the crystal growth never produces crystallite sizes much larger than the lower end of the colloidal region. Hence, the gradual release of the small amounts of energy liberated during the crystallization of γ-alumina would be extremely difficult to detect by DTA methods.

Clays and Clay Minerals; 1964 v. 13; no. 1; p. 419-428; DOI: 10.1346/CCMN.1964.0130139
© 1964, The Clay Minerals Society
Clay Minerals Society (www.clays.org)