The effect of the reaction heat on kinetic analysis by TG under a rising temperature program: Part 3

Abstract

In Parts 1 and 2 of this study (Thermochimica Acta 215 (1993) 83 and 97), the effect of the reaction heat changes on the rising temperature program was accounted for by using a relationship between the sample's temperature T and time t as a function of the degree of conversion α. The computer simulation and kinetic analysis in those publications dealt with two extreme situations. In the present study, the more common case is considered, in which the temperature recorded by the thermocouple has a value between those of the sample and the furnace. As before, a simulation of TG, DTG and T-t curves has been made, and a kinetic analysis has been achieved for the calculation of the Arrhenius parameters and the determination of the reaction mechanisms using the integral or differential methods. The results obtained show that either the kinetic parameters or the reaction mechanism changes as a result of the reaction heat. To obtain the correct mechanism and an accurate value of the kinetic parameters, it was found advantageous to use the initial decomposition data, rather than data for the whole decomposition period. The use of the initial decomposition data, however, makes it difficult to distinguish the mechanism but this can be overcome by using both single and multiple heating-rate kinetic analysis.