Isothermal and Nonisothermal Reaction Kinetics in Solids:  In Search of Ways toward Consensus

Abstract

Thermogravimetric data for the decomposition of ammonium dinitramide (ADN) have been obtained under isothermal and nonisothermal conditions in order to determine the efficacy of different methods for analyzing the kinetics of solid-state reactions. A widely used model-fitting method gives excellent fits to the experimental data but yields highly uncertain values of the Arrhenius parameters when applied to nonisothermal data because temperature and extent of conversion are not independent variables. Therefore, comparison of model fitting results from isothermal and nonisothermal experiments is practically meaningless. Conversely, model-free isoconversional methods of kinetic analysis yield similar dependencies of the activation energy on the extent of conversion for isothermal and nonisothermal experiments. Analysis of synthetic data generated for a complex kinetic model suggests that, in the general case, the identical dependencies are unlikely to result from experiments obtained under isothermal and nonisothermal conditions.