Determination of the Mechanism of Thermal Decomposition Reactions of Solids by Using the Cyclic and Constant Decomposition Rate Thermal Analysis Method

Abstract

The cyclic and Constant Rate Thermal Analysis technique (CRTA) has being used. The two rates automatically selected in the cyclic curve are small enough to allow the two states of the sample to be compared have nearly the same reacted fraction, α. Thus, the activation energy, E, can be calculated without prior knowledge of the actual reaction mechanism.

A procedure is developed for determining the kinetic law followed by the reaction by means of master curves that represent the values of α as a function of In A/C — E/RT,once E has been obtained from the cyclic CRTA diagram. The plots of α against E/RT must be superpossed upon the curve corresponding to the actual kinetic of the reaction by a lateral shift. The length of the lateral shift must be equal to In A/C, C being the constant rate and A the preexponential factor of Arrhenius. This procedure has been checked by studying the thermal decomposition of BaCO₃.