On the evaluation of kinetic parameters from thermogravimetric curves
1980; Elsevier BV; Volume: 41; Issue: 1 Linguagem: Inglês
10.1016/0040-6031(80)80101-8
ISSN1872-762X
Autores Tópico(s)Chemical Thermodynamics and Molecular Structure
ResumoWe concluded in a previous work [l] that it is not possible to determine the kinetic law followed by a thermal decomposition reaction of a solid from the kinetic analysis of a single TG curve. It is necessary to carry out at least one isothermal run to determine the actual reaction mechanism without ambiguity. It was shown from a theoretical analysis [l] that TG data of reactions following an Avrami-Erofeev law necessarily fit a first-order kinetic equation. However, it was concluded that very similar activation energies would be obtained whatever the value of the exponent n (1, 2 or 3) in the AvramiErofeev equation. Dharwadkar et al. [2] have studied the mechanism of the thermal decomposition of CdC03 and, from the analysis of both a single TG diagram and a single isothermal curve, they find that the reaction mechanism is described by an Avrami-Erofeev equation with n = 3, concluding that their results support, in part, OUT theoretical conclusions. However, they state [Z] that the apparent activation energies calculated frcm a TG diagram are quite different for different values of n, which is not in agreement with our theoretical deduction [ 11. The aim of the present note is to show that the apparent contradiction between the statement of Dharwadkar et al. and our conclusion is due to the different ways of defining the constant rate. Thus, Dharwadkar et al. [2] seem to express the Avrami-Erofeev isothermal in the form
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