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Abstract  

An improved version of the Coats-Redfern method of evaluating non-isothermal kinetic parameters is presented. The Coats-Redfern approximation of the temperature integral is replaced by a third-degree rational approximation, which is much more accurate. The kinetic parameters are evaluated iteratively by linear regression and, besides the correlation coefficient, the F test is suggested as a supplementary statistical criterion for selecting the most probable mechanism function. For applications, both non-isothermal data obtained by theoretical simulation and experimental data taken from the literature for the non-isothermal dehydration of Mg(OH)2 have been processed.

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Abstract  

A new procedure for the prediction of the isothermal behaviour of the solid-gas system from non-isothermal data is suggested. It bypasses the use of various approximations of the temperature integral that ground the integral methods of prediction. The procedure was checked for: (1) simulated data corresponding to a first order reaction; (2) experimental data obtained in the isothermal and non-isothermal decompositions of ammonium perchlorate. For the simulated data, a very good agreement between calculated isotherms and those evaluated by means of the suggested procedure was obtained. A satisfactory agreement (errors in time evaluation corresponding to a given degradation lower than 18%, for 0.10a0.37 and lower than 10% for 0.37a0.70) was obtained for the experimental data corresponding to the decomposition of ammonium perchlorate. In this last case, the mentioned differences between experimental and calculated data can be due both to the inherent errors in the evaluation of the decomposition isotherms and to the dependence of the activation energy on the conversion degree.

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-state reactions is usually described by the equation: 1 where x = E / RT and p ( x ) is termed the temperature integral and has no analytical solution. Many methods have been proposed [ 4 – 11 ] for estimating the activation energy. The most

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Journal of Thermal Analysis and Calorimetry
Authors: Marcelo Kobelnik, Douglas Lopes Cassimiro, Adélia Emilia de Almeida, Clóvis Augusto Ribeiro, and Marisa Spirandeli Crespi

temperature integral. A difficulty results from the fact that this integral does not have an exact analytical solution. Thus, it is convenient to approximate the integral of temperature for some function that yields suitable estimates to these kinetic

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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

Eq. 4 , 4 where dα/d t is the reaction rate and K the rate constant. Substituting Eq. 4 in Eq. 5 , we have: 5 integrating up to the conversion, α (at temperature T ) 6 because E /2 RT ≫ 1, the temperature integral can be approximated by

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the integral can be approximated to be infinity; i.e., (7) Here, p ( x ) is the temperature integral, where , which does not have analytical solution. Hence, the logarithmic form of Eq. 7 can be expressed as (8) The function p ( x ) is not

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form of the above Eq. 3 can be given by 4 As mentioned earlier, exact solution of the temperature integral is not available and various approximations made for this has resulted into different methods. We have discussed a few most commonly

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Preparation of the Ca–diclofenac complex in solid state

Study of the thermal behavior of the dehydration, transition phase and decomposition

Journal of Thermal Analysis and Calorimetry
Authors: Marcelo Kobelnik, Douglas Lopes Cassimiro, Clóvis Augusto Ribeiro, Diógenes dos Santos Dias, and Marisa Spirandeli Crespi

is the gas constant. Kinetic parameters are obtained by fitting Eq. 1 to experimental data. As a consequence, an evaluation of the integral on the right side of the Eq. 1 is required, known as temperature integral. A difficulty results

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Journal of Thermal Analysis and Calorimetry
Authors: Renato Vessecchi Lourenço, Marcelo Kobelnik, Clóvis Augusto Ribeiro, and Fernando L. Fernonani

the Eq. 1 is required and is known as the temperature integral. A difficulty results from the fact that this integral does not have an exact analytical solution. Thus, it is convenient to approximate the temperature integral for some function that

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most probable mechanism function g( & ), knowing as a kinetics triplet of the processes. These methods are based on the assumption concerning the temperature integral, which will bring the homologous error. In the present work simultaneous TG

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