Activation energy determination for linear heating experiments: deviations due to neglecting the low temperature end of the temperature integral

Abstract

Model-free isoconversion methods which use approximations of the temperature integral are generally reliable methods for the calculation of activation energies of thermally activated reactions studied during linear heating. These methods generally neglect the temperature integral at the start of the linear heating, I (T o ). An analytical equation is derived which describes the deviations introduced by this approximation.It is shown that for most reactions encountered this assumption does not have a significant influence on the accuracy of the method. However, in cases where T o is within about 50 to 70K of the reaction stage to be investigated and activation energies are relatively low, significant deviations are introduced. It is shown that some of the published thermal analysis work on activation energy analysis of reactions occurring at relatively low temperatures is affected by these deviations. Examples are specific cases of dehydration reactions, cure reactions and cluster formation in Al alloys.

A model for precipitation kinetics and strengthening in Al–Cu–Mg alloys

“…This activation energy should be equal to the activation energy for S phase formation, which can be derived from experiments which measure the rate of S formation at different temperatures. For the present analysis, the activation energy is obtained from DSC experiments performed on a 2024-T351 alloy at different heating rates using iso-conversion methods [57,58]. Fig.…”

Isoconversional Methodology

“…It is a reasonable assumption unless a process in question has low activation energy and becomes detectable at temperature close to the initial temperature. In such cases, neglecting the integral from 0 to T 0 may introduce some error to the estimated value of E. The issue has been studied by Starink [18], and some of the results of that study are shown in Fig. 2.2.…”

Thermal decomposition and kinetics studies on the poly (2,2-dinitropropyl acrylate) and 2,2-dinitropropyl acrylate–2,2-dinitrobutyl acrylate copolymer

“…However, the above-mentioned ASTM E698 method which is called Kissinger method has a number of important limitations that should be understood, which arise from the underlying assumptions of the method [25,26]. The E a values obtained by using this method have the systematic error.…”