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.
