Energy Changes when Kaolin Minerals are Heated

Abstract

The work outlined in this paper was undertaken toshow how, by a consideration of the energy changes involved, some insight may be gained into the reactions occurring when kaolin minerals are heated. Activation energies have been determined experimentally for the dehydration of various kaolin minerals. The fireclay mineral is dis-tinctive and it is suggested that it does not form part of a halloysite-kaolinite series. It is further thought possible that there is a series of fireclay minerals. From thermochemical and thermodynamic considerations the heat of formation of kaolinite has been calculated approximately and enthalpy and free energy changes have been estimated for the exothermic reaction at 980 ~ These indicate that, if a compound is produced uring de-hydration, the most probable xplanation of the exothermic reaction is the simultaneous production of mullite,),A1203 and SiO2. Finally the lattice nergies of kaolinite and its thermal decomposition products have been calculated.