Kissinger Method in Kinetics of Materials: Things to Beware and Be Aware of

The Kissinger method is an overwhelmingly popular way of estimating the activation energy of thermally stimulated processes studied by differential scanning calorimetry (DSC), differential thermal analysis (DTA), and derivative thermogravimetry (DTG). The simplicity of its use is offset considerably by the number of problems that result from underlying assumptions. The assumption of a first-order reaction introduces a certain evaluation error that may become very large when applying temperature programs other than linear heating. The assumption of heating is embedded in the final equation that makes the method inapplicable to any data obtained on cooling. The method yields a single activation energy in agreement with the assumption of single-step kinetics that creates a problem with the majority of applications. This is illustrated by applying the Kissinger method to some chemical reactions, crystallization, glass transition, and melting. In the cases when the isoconversional activation energy varies significantly, the Kissinger plots tend to be almost perfectly linear that means the method fails to detect the inherent complexity of the processes. It is stressed that the Kissinger method is never the best choice when one is looking for insights into the processes kinetics. Comparably simple isoconversional methods offer an insightful alternative.

Crystallization of GeO2–Al2O3–Bi2O3 Glass

In the presented work, two kinds of germanium oxide glass with different compositions, namely GeO2 and GeO2–Al2O3–Bi2O3, were investigated. After controlled crystallization of a glassy sample, the emission in the NIR-range was determined (1165 nm with excitation at 470 nm). To better understanding the kinetics of the glass crystallization, the activation energy was also determined by applying the Kissinger method. The obtained results show that in the case of GeO2–Al2O3–Bi2O3, activation energy value was 400 and 477 kJ/mol, which means that such values are significantly larger than for pure GeO2 (254 kJ/mol). The investigations also show that two phases crystallized in the complex glass matrix: the mullite-like phase and germanium oxide.

DETERMINATION OF KINETIC PARAMETERS OF CHEERY TREE PYROLYSIS USING KISSINGER METHOD

In the global quest for substitution of fossil fuels, biomass is regarded as one of the most promising alternatives. Thermochemical conversion is one of the dominant biomass-to-energy processing routes with pyrolysis as one of the options that gained importance in recent years. In this paper pyrolysis experiments of cheery tree samples were performed. The objective of this research was to determine selected physical and chemical properties of cheery related to thermochemical conversion. The samples were pyrolysed in a thermogravimetric analyzer in an inert, nitrogen, atmosphere at four different heating rates 1, 2, 5 and 10 °C/min. Pyrolysis occurred, as expected, in three step: loss of moisture and light volatiles, active and passive pyrolysis. With an increase in heating rate a lateral shift of the maximum rate of weight loss for the thermal decomposition to higher temperatures was observed, as well as an increase in the amount of residual char. Moreover, kinetic studies were performed using the Kissinger method. The activation energy was calculated to be 155.26 kJ/mol, while the pre-exponential factor was 1.685×1012 min-1. Obtained results are comparable to values reported in literature. Kissinger method is straightforward and offers the possibility for fast and reliable determination of kinetic parameters.

Study of Crystallization Kinetics of Amorphous Zirconia in Fe2O3 Matrix by Kissinger Method

The composite materials Fe2O3-ZrO2 with different content of zirconium oxide have been obtained by thermochemical synthesis. The process of crystallization of zirconium dioxide and the effect of the amount of zirconium dioxide on the phase transformation have been studied by DTA and microscopy. The activation energy of the crystallization process was calculated by the Kissinger method to be in average 170 KJ/mol. It is shown that an increase of the ZrO2 content leads to an increase of temperature of crystallization.

Thermo-kinetics of Forest Waste Using Model-Free Methods

Thermal behaviour of pine needles (Pinus Roxburghii) is examined through a thermogravimetry technique. The dried samples of pine needles undergo the non isothermal decomposition at temperature range of 308 - 1173 K. The heating rates used for experimental purposes are: 5 °C min-1, 10 °C min-1 and 15 °C min-1. Kinetic parameters of thermal decomposition reactions of pine needles are obtained through the model-free schemes. The estimated values of activation energy and frequency factor derived from Kissinger method are 132.77 kJ mol-1 and 13.15 x107 min-1, respectively. Furthermore, the averaged values of the same kinetics parameters retrieved from the isoconversional methods are 82.38 kJ mol-1 and 74.833 kJ mol-1, 25.42 x1013 min-1 and 13.449 x1010 min-1, respectively. Instead of the Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira Sunrose (KAS) schemes, the kinetic parameters derived from the Kissinger method are relatively promising for the thermal decomposition process, since the kinetic parameters are highly affected by intermediate stages and overlapping of the concurrent reaction occurred during pyrolysis.

Calculation of Kinetic Parameters of the Thermal Decomposition of Residual Waste of Coniferous Species: Cedrus Deodara

This paper deals with pyrolysis decomposition of Cedrus deodara leaves with the help of thermogravimetric analysis (TGA). Experiments are performed in the presence of inert atmosphere of nitrogen. Experiments are conducted at three different heating rates of 5 °C∙min-1, 10 °C∙min-1 and 15 °C∙min-1 within temperature range of 35 °C to 700 °C. Arrhenius parameters such as activation energy and frequency factor are estimated by Flynn Wall and Ozawa (FWO), Kissinger-Akahira-Sonuse (KAS) and Kissinger. The activation energy and frequency factor calculated by using Kissinger method are 67.63 kJ∙mol-1 and 15.06 . 104 min-1 respectively; whereas the averaged values of the same parameters through FWO and KAS methods are 89.59 kJ∙mol-1 and 84.748 kJ∙mol-1, 17.27 . 108 min-1 and 62.13 . 107 min-1 respectively. Results obtained through Kissinger method represent the actual values of kinetic parameters. Conversely, FWO and KAS methods reflect the apparent values of kinetic parameters, as they are highly influenced by the overlapping of competitive reactions occur during pyrolysis.