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Some problems concerning the evaluation of non-isothermal kinetic parameters

Solid-gas decompositions from thermogravimetric data

Journal of Thermal Analysis and Calorimetry
Authors: P. Budrugeac, Alice Luminita Petre, and E. Segal

The validity of isoconversional methods used to evaluate the activation energy is discussed. The authors have shown that the Flynn-Wall-Ozawa and Friedman methods give results that agree with each other only if the activation energy does not change with the degree of conversion. A criterion for the reaction mechanism as expressed by the differential conversion function is suggested too.

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Abstract  

A new method is reported for the evaluation of non-isothermal kinetic data for various forms of the conversion function. The algorithm is based on a pseudo-inverse matrix method. A description of the algorithm and some calculation examples are presented.

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Abstract  

Two integral isoconversional methods (Flynn–Wall–Ozawa and Kissinger–Akahira–Sunose) and the invariant kinetic parameters method (IKP) were used in order to examine the kinetics of the non-isothermal crystallisation of a silica-soda-lead glass. The objective of the paper is to show the usefulness of the IKP method to determine both the activation parameters and the kinetic model of the investigated process. Thismethod associated with the criterion of coincidence of kinetic parameters for all heating rates and some procedures of the evaluation of the parameter from Johnson–Mehl–Avrami–Erofeev–Kolmogorov (JMAEK) equation led us to the following kinetic triplet: activation energy, E=170.5±2.5 kJ mol–1 , pre-exponential factor, A=1.178±0.350·10 10 min–1 and JMAEK model (A m) m=1.5.

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Heteroleptic cadmium(II) complex, potential precursor for semiconducting CDS layers

Thermal stability and non-isothermal decomposition kinetics

Journal of Thermal Analysis and Calorimetry
Authors: Anna Kropidłowska, A. Rotaru, M. Strankowski, Barbara Becker, and E. Segal

Abstract  

Coordination compounds may be used as efficient precursors for fabrication of semiconducting layers. Thermal stability of such a potential precursor — [Cd{SSi(O-tBu)3}(S2CNEt2)]2 — was investigated (tBu means tert-butyl and Et means ethyl). The kinetic study was performed by means of different multi-heating rate methods: isoconversional (Flynn-Wall-Ozawa, Kissinger-Akahira-Sunose and Friedmann) methods associated with the criterion of the independence of the activation parameters on the heating rate. The kinetic triplet of the non-isothermal decomposition of this Cd(II) complex was established.

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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.

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Abstract

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.

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Dynamic thermal analysis of solid-state reactions

The ultimate method for data analysis?

Journal of Thermal Analysis and Calorimetry
Authors: Chao-Rui Li and Tong B. Tang

Abstract

There are many reactions of interest in which one or more of the reactants belong to some solid phases. Modern thermoanalytical instruments can conveniently provide reaction kinetic data of high precision and accuracy, from which the underlying activation energyE may be derived in principle. Unfortunately, no ‘best' method yet exists for the derivation when the data have been collected with a programmed linear increase in sample temperature, unlike the case of isothermal measurements, which however suffer from experimental limitations [1]. Here we propose a method for extractingE from non-isothermal data, that promises general validity.

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Abstract  

A model describing the roles of bound and unbound vacancies is proposed in order to predict defect decay and short-range-order kinetics of quenched binary alloys during linear heating experiments. This is an alternative treatment of a previous approach. The model has been applied to the differential scanning calorimetry (DSC) curves of Cu-5 at.% Zn quenched from different temperatures. An expression to calculate the activation energy for migration of solute-vacancy complexes was also developed which make use of DSC trace data. A value of 89.120.32 kJ mol-1 was obtained for the above alloy. The relative contribution of bound and unbound vacancies to partition of effective activation energy corresponding to the ordering process as influenced by quenching temperature was also assessed.

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Abstract  

The kinetics of thermal decomposition of Ca(H2PO4)2H2O under non-isothermal conditions was studied. The TG/DTG curves were obtained at five heating rates: 5, 7, 10, 12 and 20 K min–1. The kinetic analysis was performed by means of three methods: Friedman, Budrugeac–Segal and NPK by Sempere and Nomen. An important dependence of the activation energy vs. the conversion degree was observed and also a compensation effect. The decomposition consists of water loss and is due to the elimination of crystallization water and an intermolecular condensation, respectively.

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Abstract  

Kinetics of thermal decomposition of three structurally similar complexes Co2Cu(C2O4)3 (R-diam)2, where R is ethyl, 1,2-propyl or 1,3-propyl, was studied under non-isothermal conditions and nitrogen dynamic atmosphere at heating rates of 5, 7, 10, 12 and 15 K min−1. For data processing the Flynn-Wall-Ozawa and a modified non-parametric kinetic methods were used. By both methods the activation energy are in the range of 97–102 kJ mol−1. The formal kinetic is r=kα(1−α)2. Also a compensation effect between lnA and E was evidenced. The kinetic analysis lead to the conclusion of an identic decomposition mechanism by a single step process.

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