Formal kinetic analysis of processes in the solid state

The applicability of an unconventional approach in the formal kinetic analy sis of solid-state reactions is discussed. This approach is based on the jo int use of so-called isoconversional methods and of the non-linear regressi on analysis. By means of this approach reliable kinetic parameters for the phase transitions between three polymorphic modifications of calcium carbon ate were obtained. The influence of the conditions of sample preparation on the transition kinetics has been studied. Two different transition mechani sms are compared using the calculated kinetic data. The isoconversional met hod, proposed by Friedman, delivers activation energy values, which deviate s from data, obtained by means of the Flynn-Wall-Ozawa method. Additionally , the calculated apparent activation energy is dependent on the degree of c onversion. The influence of some model deviations on the accuracy of the is oconversional methods is discussed. It is shown that the robustness of thes e methods towards model deviations may be tested by an analysis of theoreti cal plots. (C) 1999 Published by Elsevier Science B.V. All rights reserved.