The thermal decomposition reactions of Gypsum, Lime and Limestone compounds

Abstract

A thermogravimetric study has been undertaken of the thermal decomposition of naturally-occurring Southern African gypsum, pure calcium sulphate dihydrate, synthetically prepared gypsum as well as naturallyoccurring Southern African lime, limestone and their pure compounds. The decomposition reactions proceed without any evidence of detectable melting and the reaction products are identified by using X-ray diffraction analysis and the mass loss percentages on the thermogravimetric curves. Atmospheres used are air, air/water, nitrogen, CO 2 , CO 2 /air and CO 2/water. Mass loss versus time curves of the decomposition reactions of the compounds are used to obtain the activation energy values at different heating rates and fractions decomposed. The shape of the curve of the activation energy versus fraction decomposed yields important information on the complexity of the reaction. This information together with the kinetic data, is used to select a kinetic equation which gives the best mathematical description of the individual decomposition reactions. The kinetic description of the individual decomposition reactions differs in the different atmospheres. The partial pressures of CO 2 and water vapour, also influence the thermal decomposition of the compounds.