Model Dependence of the Activation Energy Derived from Nonisothermal Kinetic Data

Abstract

This work intends to explain mathematically the model dependence of the activation energy, E a, derived from fitting nonisothermal kinetic data to a kinetic model. Artificial data following single reaction mechanisms, both isothermal and nonisothermal, were generated to fit exactly the following simulated kinetic models: first-order reaction, fourth-order Avrami−Erofeyev process, and one-dimensional diffusion. To simulate more closely experimental data, random errors, corresponding to ±0.1% of the maximum conversion value, were embedded in the data by adding a random number bounded by ±0.001 to each data point. For isothermal data, any kinetic model leads to the correct value of E a. However, for nonisothermal data, the calculated E a deviates from the correct value by an amount, ΔE a, that depends strongly on the kinetic model to which the data are fit. In addition, the apparent frequency factor depends slightly on the kinetic model for isothermal data, but depends strongly on the model for nonisothermal data. The results highlight the severe limitations of fitting nonisothermal data to kinetic models.

Thermal degradation studies and kinetic modeling of cardoon (Cynara cardunculus) pyrolysis using thermogravimetric analysis (TGA)

“…Further elaboration of the TGA results is usually carried out with various model fitting techniques, a branch of who are the iso-conversional methods. Although many of these model fitting methods tend to give highly unreliable results when applied to non-isothermal data (Zhou and Grant, 2004;Chen et al, 2006), iso-conversional methods constitute an interesting and easy-touse solution for the estimation of the kinetic parameters, providing the user with rather accurate results compared to the other model fitting methods.…”

Mechanisms controlling primary crystallisation of Ga20Te80 glasses

“…Differential scanning calorimetry (DSC) has been widely used for the determination of both the thermal stability of the glassy alloys and the apparent activation energy of crystallisation through the so-called Kissinger plot [1] or Ozawa plot [2]. More controversial is the use of the Kolmogorov-Johnson-Mehl-Avrami (KJMA) model [3][4][5][6][7] to examine the kinetics of primary crystallisation in a glassy alloy from continuous heating DSC data, see for instance papers [8][9][10][11][12][13], and references cited therein.…”

The Thermal Decomposition of Ammonium Meta-Vanadate under Restricted Flow Conditions

“…There has been considerable debate about the best method for obtaining the kinetic triplet [1]- [17]. In an effort to mitigate these problems, several "new" approaches have been presented for obtaining the kinetic triplet during the past 15 years to obtain more reliable data as shown by [8]- [17] and the references therein. Often, these new methods have established that the "simple decompositions" occur through several mechanistic steps.…”