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.
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.
Authors:C. Păcurariu, R. I. Lazău, I. Lazău, D. Tiţa, and A. Dumitrel
-state reactions is usually described by the equation:
where x = E / RT and p ( x ) is termed the temperatureintegral and has no analytical solution.
Many methods have been proposed [ 4 – 11 ] for estimating the activation energy. The most
Authors:Marcelo Kobelnik, Douglas Lopes Cassimiro, Adélia Emilia de Almeida, Clóvis Augusto Ribeiro, and Marisa Spirandeli Crespi
temperatureintegral. 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
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 ,
where dα/d t is the reaction rate and K the rate constant. Substituting Eq. 4 in Eq. 5 , we have:
integrating up to the conversion, α (at temperature T )
because E /2 RT ≫ 1, the temperatureintegral can be approximated by
the integral can be approximated to be infinity; i.e.,
Here, p ( x ) is the temperatureintegral, where , which does not have analytical solution. Hence, the logarithmic form of Eq. 7 can be expressed as
The function p ( x ) is not
form of the above Eq. 3 can be given by
As mentioned earlier, exact solution of the temperatureintegral is not available and various approximations made for this has resulted into different methods. We have discussed a few most commonly
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 temperatureintegral. A difficulty results
Authors:Renato Vessecchi Lourenço, Marcelo Kobelnik, Clóvis Augusto Ribeiro, and Fernando L. Fernonani
the Eq. 1 is required and is known as the temperatureintegral. A difficulty results from the fact that this integral does not have an exact analytical solution. Thus, it is convenient to approximate the temperatureintegral for some function that
most probable mechanism function g( & ), knowing as a kinetics triplet of the processes. These methods are based on the assumption concerning the temperatureintegral, which will bring the homologous error.
In the present work simultaneous TG