The applicability of DTA and DSC techniques to the study of the kinetics of phase transition reactions

Abstract

Differential thermal analysis and differential scanning calorimetry techniques have been used to study the kinetics of phase transitions. The aragonite/calcite transformation was chosen as test reaction.Marked discrepancies were observed between the DTA kinetic results and those obtained from isothermal kinetic measurements. This disagreement is associated with the difficulty of determining accurately the reaction rate of the process from a DTA cHrve.In contrast, in DSC measurements, where the reaction rate is given by the height of the peak from the base-line, it is possible to get a satisfactory fit of the data, and the kinetic results obtained with this technique are in good agreement with the isothermal ones.The valuation of kinetic parameters of phase transitions and crystallization processes from DTA curves has received the attention of many investigators in recent years. In this respect, mention should be made of the new interest shown by Marotta et al. [1][2][3][4] and other authors [5][6][7][8] in the applicability of the Piloyan [9] and Kissinger [10] methods to the analysis of the kinetics of these reactions.On the other hand, in a recent review on polymorphic transition kinetics by DTA, Dollimore et al. [11 ] point out that DTA "offers a suitable method of determining the mechanism of a reaction which does not involve a weight change or change in physical state-parameters that afford the classical isothermal approach of determining reaction kinetics '' .The aim of the present paper is to deepen the knowledge of the application of DTA to study phase transition mechanisms, and also to explore the usefulness of DSC technique for the kinetic study of such reactions.The aragonite/calcite transformation was chosen as the test reaction. In order to obtain reliable kinetic data on the transformation for comparison with kinetic parameters obtained with these techniques, kinetic analysis of the aragonite ~ calcite (A ~ C) transformation was also carried out under isothermal conditions.

Modeling the Thermal Decomposition of Solids on the Basis of Lattice Energy Changes

“…A dislocation glide mechanism (42), whereby motion of a partial dislocation causes a shear of the Ca> sublattice, has been proposed. The kinetics of the aragonite-calcite transformation have been extensively studied (38,(42)(43)(44)(45)(46)(47)(48)(49)(50)(51). The transition has a small, positive enthalpy change ( H from 0.21 to 4.88 kJ mol\), but has a high activation energy (E from 160 to 750 kJ mol\).…”