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Abstract  

Activation energy is calculated from a single curve of a derivative of mass loss perturbed by a sinusoidal modulation of a temperature-time relationship. The method is based on a prediction of a hypothetical derivative of mass loss that corresponds to the absence of this modulation (perturbation). Simple considerations show that the unperturbed derivative coincides with the modulated derivative at inflection points of the modulated temperature-time relationship. The ratio of the perturbed and unperturbed derivatives at the points of time corresponding to maxima and minima of the sinusoidal component of the modulated temperature immediately leads to activation energy. Accuracy of the method grows with decreasing in the amplitude of the modulation. All illustrations are prepared numerically. It makes possible to objectively test the method and to investigate its errors. Two-stage decomposition kinetics with two independent (parallel) reactions is considered as an example. The kinetic parameters are chosen so that the derivative of mass loss would represent two overlapping peaks. The errors are introduced into the modulated derivative by the random-number generator with the normal distribution. Standard deviation for the random allocation of errors is selected with respect to maximum of the derivative. If the maximum of the derivative is observed within the region from 200 to 600C and the amplitude of the temperature modulation is equal to 5C, the error in the derivative 0.5% leads to the error in activation energy being equal to 2-6 kJ mol-1. As the derivative vanishes, the error grows and tends to infinity in the regions of the start and end of decomposition. With the absolute error 0.5% evaluations of activation energy are impossible beyond the region from 5 to 95% of mass loss.

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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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Isoconversional analysis of solid state transformations

A critical review. Part II. Complex transformations

Journal of Thermal Analysis and Calorimetry
Authors:
J. Farjas
and
P. Roura

assumptions. Moreover, we will provide some piece of advice to manipulate experimental data to apply isoconversional methods properly. Non-constancy of the activation energy Originally isoconversional methods were based on the

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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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been used widely to estimate the kinetic parameters of degradation processes, such as activation energies ( E ), reaction order ( n ), and the Arrhenius pre-exponential factor ( A ) [ 17 – 19 ], which can be calculated using various kinetic models such

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Journal of Thermal Analysis and Calorimetry
Authors:
F. M. Aquino
,
D. M. A. Melo
,
R. C. Santiago
,
M. A. F. Melo
,
A. E. Martinelli
,
J. C. O. Freitas
, and
L. C. B. Araújo

. The objective of this study is to study the thermal degradation of the ligand groups with the metallic ions of the system using the Flynn and Wall and “Model-free kinetics” methods and evaluate the results in order to establish the activation energy as

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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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Abstract  

In this short communication, a recent article published in the Journal of Thermal Analysis and Calorimetry, which presents an erroneous conclusion based on incorrect calculations, is critically discussed. Since the observations made in that report are based on part of the content of a publication of my authorship, trying to reject some expressions I presented, obviously it came to my attention. This brief note emphasizes that some of the arguments used and the main conclusion stressed in the manuscript under discussion are wrong and must be dismissed.

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(activation energy, pre-exponential factor, and conversion function) of each degradation step is one important target of kinetic investigations. Many kinetic analysis methods have been developed, among which isoconversional methods have been widely used [ 1

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Abstract  

The effect of some alkali metal bromides, iodides and sulphates on the diffusion of bromide, iodide and thallium ions, respectively, is studied at various temperatures. The activation energy required for the process of diffusion of these three ions in different supporting electrolytes have been calculated. It is found that activation energy for a given ion decreases in the reverse order of the charge density of alkali metal ions of the supporting electrolyte. This observed trend in activation energy is explained qualitatively by considering the distortion in the water structure caused by these ions and agar molecules.

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