The quandary aspects of non-isothermal kinetics beyond the ICTAC kinetic committee recommendations

• Generalized degree of conversion along with the proximity to equilibrium are needed for advanced kinetic evaluation.
• Geometric reaction models discrimination can become outmoded when using schematic two-parameter attitude.
• Logistic and model-free approaches together with Arrhenius and non-Arrhenius pattern are shown longsighted.
• Temperature gradients and yet unsolved thermal inertia effect are considered indispensable.

The paper discusses of some issues of thermoanalytical kinetics that have not been addressed in the previously published CTAC kinetic recommendations. Namely the true nonequilibrium degree of conversion, factual and fictional modeling, nucleation-growth exponents, cold crystallization, effect of undercooling, logistic equations, model-free methods, meaning of activation energy, Arrhenius and non-Arrhenius approach, thermal gradients, misfit of Kissinger method and the true meaning of temperature measured during rapid temperature changes. Insensitiveness of traditional kinetic model discrimination is attributable to the equivalency of exploited plots (from 1/T to divergent T—legitimate for a narrow temperature interval) and further smoothing effect due to using logarithm. The most important impact on kinetic data evaluation is a persisting neglect of thermal inertia when evaluating DTA peaks presented on every occasion of real measurements. The majority of 149 references are focused on papers published in Thermochimica Acta.

The analysis of a DTA curve ↑DT(t) vs. → t and its first (dΔT/dt) and the second (d2ΔT/dt2) derivatives are shown during a model of exothermic process under heating. They exhibits the curves shape characteristics viewing distinctive points such as apexes (Δ) and inflections (◊). It provides general basis for a better understanding of the peak rectification (middle) when assuming the impact of heat inertia (≈dΔT/dt, dashed violet) which causes the peak distortion (right): altered areas (green shaded) and apex misfit correlated to the extrapolated linear background (black dotted). It is approved by an experiment (right) where the sample was operationally subjected by definite heat pulses (dotted red), either electrically by resistivity micro-heater inside the sample or by externally applied laser pulses [122] both displaying similar character of a DTA-like response (dashed blue) which under the rectification for heat inertia is shifted closer to the original impute (green full). Still little misfit between red pulse and green rectified curve (orange) is due to the yet unincorporated temperature gradients.Figure optionsDownload as PowerPoint slide