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The high-temperature phase transition of K2SeO4 was studied by using differential thermal analysis. The Kissinger equation and the Mahadevan approximation were applied to evaluate the effective phase transition activation energy (E). The average value ofE was 12.85 ±0.04 eV.

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Activation energies (E) of the thermal decomposition and the initial valuesT D of the exotherms are determined for trinitroaniline, trinitro-m-phenylenediamine, trinitrotriaminobenzene, trinitrophenol, trinitroresorcinol, trinitro-m-cresol and hexanitrooxanilide. Linear relationships are derived between the termsE.T D 1− and published kinetics data on these compounds, obtained by an isothermal manometric method. The mechanisms of the primary steps in the thermolyses of these polynitro compounds are discussed. A positive influence on their thermal stability has been confirmed, arising from the contact of the measured compounds with the glass surface.

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Abstract  

When ethylene-vinyl acetate copolymer, EVA, is heated, a two-stage thermal degradation occurs following its melting. The vinyl acetate content of the copolymer was determined to be 43.8% by using TA 2950 and TA 2050 thermogravimetric instruments. TG/FTIR was used to detect the evolved gas. Acetic acid and trans-1-R-4-R'-cyclohexane were the main products evolved from EVA in the first and second stage, respectively. The apparent activation energies were determined for both stages by differential methods.

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Abstract  

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.

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A simple approach to determine the activation energy (E) of solid-state decomposition reactions is described. The activation energy is calculated from the slope of the logarithm of the maximum peak height of the isothermal DTA trace versus the reciprocal of the absolute temperature. The proposed method is applied in the study of the kinetics of thermal decomposition of cadmium carbonate. The activation energy calculated from this method (90.8±2.2 kJ mole−1) is in very good agreement with the value (87.5±2.5 kJ mole−1) obtained by the conventional method.

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Abstract  

The results of determination of activation energies (EA) of polymeric cable insulations obtained by conventional methods (usually based on the evaluation of changes of mechanical properties of insulations after their ageing in thermal chamber at different temperatures) have been compared with results obtained by methods employing the differential scanning calorimetry (DSC). Three DSC methods have been tested: the method according the ASTM E 698; measuring of DSC characteristics in the isothermal mode at several different temperatures; and the method based on evaluation of DSC characteristics of insulations after their thermal ageing in thermal chamber. The last method — which can be called as a modified conventional method, because instead of mechanical properties, the DSC characteristics are determined — has been found as most acceptable and giving similar values of EA as the other conventional methods.

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Results obtained on the thermooxidative degradations of LDPE (low-density polyethylene) and NBR (nitrile-butadiene rubber) are presented. The activation energies for the thermooxidations leading to solid products were estimated. For LDPE, the activation energies obtained from non-isothermal data are in satisfactory agreement with those obtained from isothermal data. For NBR, the isothermal activation energy is ≉16% higher than the non-isothermal one. This difference is due to the morphological changes undergone by NBR during its heating at the rather high temperatures at which isothermal measurements were performed.

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Abstract  

Poly(bisphenol A acryloxyethyl phosphate) (BPAAEP) was blended in different ratios with a commercial urethane acrylate to obtain a series of UV curable flame-retardant resins. The thermal oxidative degradation mechanism of their cured films in air were studied by thermogravimetric analysis at several heating rates between 5 and 20�C min−1. The activation energies were determined using Kissinger method, Friedman method, Flynn-Wall method, Horowitz-Metzger method and Ozawa method. The results showed that the activation energies of the blends were lower than that of pure urethane acrylate at lower degree of degradation, whereas the higher activation energies were obtained at higher degree of degradation.

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Augis and Bennett (J. Thermal Anal. 13 (1978) 283.) [6] recently proposed a modified Kissinger method for determining the activation energy of a transformation. It is shown that the proposed method was, in fact, based upon a modification to the equation for the rate of reaction under non-isothermal conditions. The apparent discrepancy between the proposed method and the original Kissinger method is therefore resolved. The modified rate equation appears to have, at best, only a limited application. However, if the equation should be appropriate for a particular transformation, it is demonstrated that Augis and Bennett's method would be the correct method for determining the activation energy.

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Thermal decomposition of hydromagnesite

Effect of morphology on the kinetic parameters

Journal of Thermal Analysis and Calorimetry
Authors:
D. Bhattacharjya
,
T. Selvamani
, and
Indrajit Mukhopadhyay

controlled hydrothermal and simple precipitation process using MgCl 2 precursor [ 28 , 29 ]. The kinetic parameters were deduced by the model-free Friedman isoconversion and Flynn–Wall method. The dependence of the activation energy on the morphology is

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