Summary The thermal behavior of KH2PO4, NaH2PO4 and Na2HPO4 under non-isothermal conditions using TG method with different heating rates was studied. The values of the reaction rate were processed by means of Friedman’s differential-isoconversional method. A dependence of the activation energy vs. conversion was observed. Therefore a procedure based on the compensation effect (suggested by Budrugeac and Segal) was applied. A less speculative data processing protocol was offered by the non-parametric kinetics method suggested by Serra, Nomen and Sempere. Three steps were observed by non-isothermal heating: a dehydration, a dimerization and a polycondensation. The differences in the intimate reaction mechanism are determined by the initial number of water molecules.
A kinetic study of the crystallization of poly(ethylene oxide) (PEO) and of a blend of PEO+poly(bisphenol A-co-epichlorohydrin)
(PBE) was performed by using DSC in a non-isothermal program at constant cooling rates. The curves obtained were analyzed
by the Kissinger, Ozawa and Friedman methods, with determination of the kinetic parameters in each case. As a consequence
of the presence of PBE, the kinetic parameters were altered, leading to the conclusion that PBE has some influence on the
crystallization of PEO, modifying its mechanism.
A differential isoconversional non-linear procedure for evaluating activation energy from non-isothermal data is suggested.
This procedure was applied to model reactions (simulations) and to the dehydration of CaC2O4⋅H2O. The results were compared with those obtained by other isoconversional methods.
Authors:T. Vlase, Gabriela Vlase, Nicoleta Birta, and N. Doca
A comparative kinetic analysis on the thermal decomposition of tartaric acid and potassium tartrate under non-isothermal conditions
was performed. The non-isothermal kinetic parameters were determined by the following four methods: integral isoconversional
method suggested by Flynn-Wall-Ozawa (FWO method); differential isoconversional method suggested by Friedman; Budrugeac-Segal
method and Non-Parametric-Kinetic (NKP) method suggested by Sempere and Nomen and modified by Vlase and Doca. The comparison
of the results obtaining by these methods leads to interesting conclusions. The experimental data were obtained in dynamic
nitrogen atmosphere at heating rates of 5, 7, 10, 12 and 15 K min−1. The less speculative kinetic analysis was possible by the NPK method.
Authors:Daqing Wang, Baoxue Zhou, Yuanjang Jia, Feng Shi, and Yiping Fan
The complex Mn(Nica)2Cl2 (Nica=nicotinamide) was prepared, and its decomposition was studied by means of TG and DSC. The IR spectra of the products
of thermal decomposition were examined at every stage. Kinetic analysis of the first stage of thermal decomposition was performed
via the TG-DTG curves, and the kinetic parameters were obtained from analysis of the TG-DTG curves with integral and differential
methods. The most probable kinetic function was suggested from a comparison of the kinetic parameters. Mathematical expressions
were derived for the kinetic compensation effect.
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.
Authors:P. Budrugeac, D. Homentcovschi, and E. Segal
The differential and integral isoconversional methods for evaluation the activation energy, described in the first note of
this series, were applied for:
a) simulated data for two successive reactions;
b) dehydration of calcium oxalate monohydrate.
It was shown that for these systems the activation energy depends on the conversion degree as well as on the method of evaluation.
A nonlinear algorithm has been suggested to increase the accuracy of evaluating the activation energy by the integral isoconversional method. A minor modification of the algorithm has made it possible to adapt the isoconversional method for an arbitrary variation of the temperature. This advanced isoconversional method allows for trustworthy estimates of the activation energy when the thermal effect of a reaction makes the temperature of a sample deviate from a prescribed heating program.
This paper is a review of some of the controversial kinetic aspects of thermal analysis, starting from the ‘šesták questions’
posed in 1979 and looking at developments in some areas since that time. Aspects considered include: temperature programmes
and variations, models and mechanisms, kinetic parameters, distinguishability and extent of fit of kinetic models, complementary
evidence for kinetic models, the Arrhenius equation and the compensation effect. The value of the ideas of non-isothermal
kinetics in chemical education is emphasized.
A calculation technique based on the SVD algorithm is suggested for solving non-isothermal kinetics problems. The uncertainties in the sought parameter values are obtained by superimposing random (Gauss) noise on experimental dependences.