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All You Need to Know about the Kinetics of Thermally Stimulated Reactions Occurring on Cooling

Department of Chemistry, University of Alabama at Birmingham, 901 S. 14th Street, Birmingham, AL 35294, USA
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Author to whom correspondence should be addressed.
Molecules 2019, 24(10), 1918; https://doi.org/10.3390/molecules24101918 (registering DOI)
Received: 1 May 2019 / Revised: 17 May 2019 / Accepted: 17 May 2019 / Published: 18 May 2019
(This article belongs to the Special Issue Thermal Analysis Kinetics for Understanding Materials Behavior)
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Abstract

In this tutorial overview article the authors share their original experience in studying the kinetics of thermally stimulated reactions under the conditions of continuous cooling. It is stressed that the kinetics measured on heating is similar to that measured on cooling only for single-step reactions. For multi-step reactions the respective kinetics can differ dramatically. The application of an isoconversional method to thermogravimetry (TGA) or differential scanning calorimetry (DSC) data allows one to recognize multi-step kinetics in the form of the activation energy that varies with conversion. Authors’ argument is supported by theoretical considerations as well as by experimental examples that include the reactions of thermal decomposition and crosslinking polymerization (curing). The observed differences in the kinetics measured on heating and cooling ultimately manifest themselves in the Arrhenius plots of the opposite curvatures, which means that the heating kinetics cannot be used to predict the kinetics on cooling. The article provides important background knowledge necessary for conducting successful kinetic studies on cooling. It includes a practical advice on optimizing the parameters of cooling experiments as well as on proper usage of kinetic methods for analysis of obtained data. View Full-Text
Keywords: activation energy; Arrhenius equation; cooling; crosslinking; decomposition; isoconversional method; model-free kinetics; rate constant activation energy; Arrhenius equation; cooling; crosslinking; decomposition; isoconversional method; model-free kinetics; rate constant
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Liavitskaya, T.; Vyazovkin, S. All You Need to Know about the Kinetics of Thermally Stimulated Reactions Occurring on Cooling. Molecules 2019, 24, 1918.

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