On the evaluation of the nonisothermal kinetic parameters of (GeS2)0.3(Sb2S3)0.7 crystallization using the IKP method

The isoconversional method suggested by Friedman and the invariant kinetic parameters method (IKP) were used in order to examine the kinetics of the nonisothermal crystallization of (GeS₂)_0.3(Sb₂S₃)_0.7. The objective of the paper is to show the usefulness of the IKP method both for determining the activation parameters as well as the model of the investigated process. It was shown that the kinetic triplet [(E, A, f(α), where E is the activation energy, A is the preexponential factor, and f(α) is the differential function of conversion], which results through the application of the IKP method, depends on the set of kinetic models considered. For different sets of kinetic models, proportional values of f(α) are obtained. A criterion for the selection of this set, the use of which lead to the true kinetic triplet corresponding to the analyzed process (E = 163.2 kJ mol^?1; A = 2.47 × 10¹² min^?1 and the Avrami‐Erofeev model, A_m, for m = 2.5–2.6 was suggested. © 2004 Wiley Periodicals, Inc. Int J Chem Kinet 36: 309–315, 2004     

Thermal Degradation of Polychloroprene Rubber Under Isothermal and Non-Isothermal Conditions

The results of a kinetic investigation of the non-isothermal degradation and the isothermal degradation of the residual deformation under constant deflection for polychloroprene rubber are presented. A relationship was derived between the degree of non-isothermal conversion and the value of the investigated mechanical property. This revised version was published online in July 2006 with corrections to the Cover Date.     

The effect of the hydration degree on the hydrothermal and thermo-oxidative stability of some collageneous matrices

The methods of the thermal analysis (TG, DTG and DTA) were used in order to investigate the effect of the hydration degree on the thermal behaviour of some collageneous matrices. It was pointed out that the degradation of hydrated collagen in the temperature range 20-400°C occurs through two successive processes accompanied by mass losses. The first process, consisting in the collagen dehydration, is endothermic and takes place in the temperature range ≈25 - ≈125°C. The second process is exothermic and consists in the decomposition and/or thermo-oxidation of dry collagen. The thermal parameters of both processes depend on the hydration degree of collagen. The observed dependencies show that the hydrothermal and thermo-oxidative stability of collagen are strongly correlated with its water content. This revised version was published online in July 2006 with corrections to the Cover Date.     

Some methodological problems concerning nonisothermal kinetic analysis of heterogeneous solid–gas reactions

Isoconversional methods, those using only one curve α = α(T) (α is the conversion degree and T is the temperature), and invariant kinetic parameter method were applied to estimate the kinetic parameters from the following nonisothermal data: (1) simulated TG curves for a single reaction; (2) TG curves for thermal degradation of PVC; and (3) TG curves for the dehydration of CaC₂O₄·H₂O. The results obtained by applying various methods for the same system are compared and discussed. Finally, a procedure of kinetic analysis is suggested. Its application could lead to kinetic parameter values that can be used to predict either α = α(t) curves for other heating rates or α = α(T) curves for isothermal conditions. © 2001 John Wiley & Sons, Inc. Int J chem Kinet 33: 564–573, 2001     

Kinetics of the complex process of thermo-oxidative degradation of poly(vinyl alcohol)

The thermo-oxidative degradation of poly(vinyl alcohol) (PVA) has been investigated by TG+DTG+DTA simultaneous analysis performed in static air atmosphere, at four heating rates, namely 3, 5, 10 and 15 K min⁻¹. TG, DTG and DTA curves showed that, in the temperature range 25–700°C, four successive processes occur. The first process consisting in the loss of physical adsorbed water is followed by three processes of thermal and/or thermo-oxidative degradations. The processing of the non-isothermal data corresponding to the second process (the first process of thermo-oxidation) was performed by using Netzsch Thermokinetics — A Software Module for Kinetic Analysis. The dependence of the activation energy evaluated by Friedman’s isoconversional method on the conversion degree shows that the investigated process is complex one. The mechanism of this process and the corresponding kinetic parameters were determined by Multivariate Non-linear Regression Program and checked for quasi-isothermal experimental data. It was pointed out that the first process of thermo-oxidation of PVA consists in three consecutive steps having Avrami-Erofeev kinetic model. The obtained results can be used for prediction of the thermal lifetime of PVA corresponding to a certain temperature of use and an endpoint criterion.     

Thermal analysis of two types of dextran-coated magnetite

The thermal stability of two kinds of dextran-coated magnetite (dextran with molecular weight of 40,000 (Dex40) and 70,000 (Dex70)), obtained by dextran adsorption onto the magnetite surface is investigated in comparison with free dextran in air and argon atmosphere. The thermal behavior of the two free dextran types and corresponding coated magnetites is similar, but atmosphere dependent. The magnetite catalyzes the thermal decomposition of dextran, the adsorbed dextran displaying lower initial decomposition temperatures comparative with the free one in both working atmospheres. The dextran adsorbed onto the magnetite surface decomposes in air through a strong sharp exothermic process up to ~450 °C while in argon atmosphere two endothermic stages are identified, one in the temperature range 160–450 °C and the other at 530–800 °C.     

On Some Obvious Cases of Incorrect Choice of the Rate Equation for Non-isothermal Kinetics

Journal of Thermal Analysis and Calorimetry -     

On the use of Diefallah's composite integral method for the non-isothermal kinetic analysis of heterogeneous solid-gas reactions

The paper contains an analysis of the used of Diefallah's composite integral method of kinetic parameters evaluation. It is shown that the application of this method should be preceded by the application of an isoconversional method through which the dependence of the activation energy, E, on the conversion degree,<span style='font-size:10.0pt; font-family:"SymbolProp BT";mso-bidi-font-family:"SymbolProp BT"'>a, should be established. If Edepends on<span style='font-size:10.0pt;font-family:Symbol;mso-bidi-font-family:Symbol'>a, Diefallah's composite integral method leads to erroneous results. If Edoes not depend on<span style='font-size: 10.0pt;font-family:"SymbolProp BT";mso-bidi-font-family:"SymbolProp BT"'>a, the true kinetic model should be comprised in the pre-established set of kinetic models. These observations were checked for two sets of non-isothermal data, namely: (a) the TG curves corresponding to the dehydration of CaC₂O4·H₂O; (b) the TG curves corresponding to the thermal decomposition of polyvinyl chloride (PVC).