Modification of the integral isoconversional method to account for variation in the activation energy

Abstract

ABSTRACT:Integral isoconversional methods may give rise to noticeable systematic error in the activation energy when the latter strongly varies with the extent of conversion. This error is eliminated by using an integration technique that properly accounts for the variation in the activation energy. The technique is implemented as a modification of the earlier proposed advanced isoconversional method [Vyazovkin, S. J Comput Chem 1997, 18, 393]. The applications of the modified method are illustrated by simulations as well as by processing of data on the thermal decomposition of calcium oxalate monohydrate and ammonium nitrate.

Thermal behavior and pyrolytic degradation kinetics of polymeric mixtures from waste packaging plastics

“…This issue is discussed through the kinetics analysis, which allows determining the reaction time of degradation needed in turn to evaluate the reactor geometry. In this study pyrolysis was studied from a kinetic point of view by processing non-isothermal TG data by applying two model-free isoconversional multiple-heating rate methods for the calculation of E a : Kissinger-Akahira-Sunose (KAS) [35] and the modified Vyazovkin methods [36][37][38]. All isoconversional methods are based on the principle that the reaction rate at constant extent of conversion is only a function of temperature and that the thermal degradation occurs by a single step mechanism.…”

“…Further increase in the accuracy can be accomplished by using numerical integration. Vyazovkin proposed a numerical integration of Equation (4) [ [36][37][38], based on the minimization of the following function (see Equations (6) and (7)) for each α:…”

Kinetics of the chrysotile and brucite dehydroxylation reaction: a combined non-isothermal/isothermal thermogravimetric analysis and high-temperature X-ray powder diffraction study

“…This is commonly done by the help of model-free methods such as the used integral (e.g. Ozawa 1965;Flynn and Wall 1966;Vyazovkin 1996Vyazovkin , 2001) and differential isoconversional (Friedman 1964) approaches which allow to determine the kinetic parameters (E a , A) independent of a discrete assumption on either an integral g(α) or differential f(α) model function. In case of an almost constant apparent E aα , it is possible to use the z(α) master plot method to determine the rate-limiting mechanism, provided that the same step controls the rate over the entire reaction progress.…”

Non-isothermal cure and exfoliation of tri-functional epoxy-clay nanocomposites

“…There has been considerable discussion in the literature about the numerous methods for the evaluation of the kinetic parameters, and in particular of the activation energy [25]. For example, Starink [26] gives an extensive comparison of methods for the analysis of constant heating rate experiments, and concludes that so-called 'Type B' methods, such as those due to Ozawa [27] and Vyazovkin [28,29], in which some approximations of the temperature integral are made, are often to be preferred to those methods (Type A), such as the Friedman isoconversional method, which make no such approximations, in particular as a consequence of uncertainty in the application of a baseline to the experimental data. Accordingly, here we adopt the most commonly used Type B method, the Kissinger method [30,31], for the determination of the activation energy.…”