Evaluation of Kinetic Parameter Calculation Methods for Non-Isothermal Experiments in Case of Varying Activation Energy in Solid-State Transformations / Neizotermisko Eksperimentu Kinētisko Parametru Noteikšanas Metožu Izvērtēšana Mainīgas Aktivācijas Enerģijas Gadījumā Cietfāžu Pārvērtībām

Abstract

Simulations of solid-state transformation kinetics were carried out calculating temperature and conversion degree for non-isothermal experiments with different heating rates. Simulations were divided in two parts: with constant and with variable activation energy. Simulations were analyzed with widely used model-based and model-free activation energy determination methods, frequency factor and kinetic model determination methods. Much of the attention was devoted to the calculation of kinetic models and frequency factors, as a more difficult and less developed step. For simulations where activation energy did not change all activation energy determination methods were found to give correct results. However, much attention should be devoted to frequency factor determination, because incorrect results would lead to problems in determination of kinetic models. For simulations where activation energy changes, correct activation energy can be determined only by differential methods or integral methods using numerical integration over small intervals. Isokinetic relationship coefficients b and c were more accurately determined with the average linear integral method. Correct kinetic model determination was possible only when coefficients b and c were accurate, and only by analyzing results of all available methods.