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]. This model (Kissinger) is also employed to study the thermal stability of current CdS/PMMA system in terms of activation energy which is given by the following relation: 2 where α is the heating rate, C is constant, and E t is the glass

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Meaningful activation energies for complex systems II

Evaluation of the Friedman method when applied to multiple reactions, and comparison with the Ozawa-Flynn-Wall method

Journal of Thermal Analysis and Calorimetry
Author: D. R. Dowdy

The validity of the Friedman method is assessed for systems of overlapping reactions. By means of mathematical analysis and numerical examples it is shown that, in the case of competitive reactions, the method gives the true value of the instantaneous mean activation energy. However, some error may be incurred if this method is applied to systems of independent reactions. The relative accuracy of the Friedman and Ozawa-Flynn-Wall methods is discussed in respect of complex systems of reactions.

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The measurement of meaningful activation energies

Using thermoanalytical methods. A tentative proposal

Journal of Thermal Analysis and Calorimetry
Authors: M. Reading, D. Dollimore, J. Rouquerol, and F. Rouquerol

The uncertainty surrounding the significance of the measured kinetic parameters of solid state decomposition reactions is discussed briefly. Some suggestions are made about what precautions should be taken in order to favour the measurement of undistorted results. Some criteria are proposed for deciding whether a measuredE value can be considered to have its usual meaning. The results of a series of experiments aimed at measuring the activation energy of the decomposition of calcium carbonate using a variety of methods, sample sizes and experimental conditions are presented. These results are compared with results found in the literature and it is concluded that it is possible to measure a reproducible value forE and it is tentatively proposed that this value is meaningful in terms of the energy barrier model of chemical reaction kinetics.

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to calculate thermodynamic parameters such as change in activation energy for dipole orientation Δ G* , enthalpy Δ H* , entropy of activation Δ S* , and the other temperature dependent parameters such as relaxation time τ , the distribution parameter

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Summary  

Activation energy was experimentally determined using the curve-fitting, initial-rise and the peak-shape methods involving pulse annealing experiments in NaCl samples irradiated at 10, 20, 30 and 40 Gy beta-doses and infrared stimulated luminescence (IRSL) signal at a temperature range of 100-300 °C. It was observed that the activation energy for NaCl decreases as the dose increased. The results were compared to other studies and discussed.

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Journal of Thermal Analysis and Calorimetry
Authors: L. Núñez-Regueira, M. Villanueva, and I. Fraga-Rivas

Abstract  

The study of the degradation of a polymer is important because it can determine the upper temperature limit, the mechanism of a solid-state process, and the life-time for this system. Since the behavior of thermosets is affected by the selection of the curing cycle, it is important to investigate the changes which take place during the thermal degradation of these materials when a change on the sequence of time and temperature is introduced during the curing reaction. In this work, the thermal degradation of two epoxy systems diglycidyl ether of bisphenol A (BADGE n=0)/1, 2 diamine cyclohexane (DCH) cured through different sequences of time and temperature was studied by thermogravimetric analysis in order to determine the reaction mechanism of the degradation processes, and also to check the influence of the curing cycle on this mechanism. Values obtained using different kinetic methods were compared to the value obtained by Kissinger’s method (differential method which do not require a knowledge of the n-order reaction mechanism), and to that obtained through Flynn–Wall–Ozawa method in a previous work.

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Abstract  

Activation energies for electrolyte diffusion of Zn(NO3)2, ZnBr2 and ZnI2 in 1% agar gel at different concentrations are determined by the least-squares fitting of the diffusion coefficient data obtained at various temperatures through the Arrhenius plots. Energy of activation is found to decrease with an increase in electrolyte concentration. This trend is explained by considering the changes in the physical properties of the solution with concentration at microscopic level, as envisaged in Wang's model.

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Abstract  

The object of this work is the quantitative explanation of linear correlation between activation energy (E), initial decomposition temperature (T i) and ionic potential (V i), observed for thermal degradation of some complexes of transitional metals. The proposed model allowed the evaluation of characteristic parameter proportional to the activation free enthalpy and also the variation of effective electrical charge (ΔQ *) of ligand, in the formation process of the activated complex. These results are satisfactory, taking into account that we utilized many simple hypotheses for deduction of Arrhenius equation.

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Abstract  

Activation energies of ignition for the thermokinetic oscillations obtained during the heterogeneous catalytic oxidation of ethanol on Pd/Al2O3 in a dynamic calorimeter were obtained using the minimum values of the temperature oscillations. These activation energies of ignition are greater than the activation energies of the corresponding oscillations. The obtained results are discussed by assuming a PdOx redox cycle.

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Abstract  

An analysis is presented of the consequences of the use of a one term equation containing apparent activation parameters, instead of the true rate equation to describe two successive decomposition reactions undergone by a solid compound. It is demonstrated that the apparent activation energy, obtained by means of isoconversional differential and integral methods, varies with the conversion degree for a relatively narrow temperature range and with temperature at a given value of the conversion degree. The activation energy values obtained with the isoconversional differential method are higher than the corresponding values obtained with the isoconversional integral method.

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