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Abstract  

A new approximate formula for temperature integral is proposed. The linear dependence of the new fomula on x has been established. Combining this linear dependence and integration-by-parts, new equation for the evaluation of kinetic parameters has been obtained from the above dependence. The validity of this equation has been tested with data from numerical calculating. And its deviation from the values calculated by Simpson's numerical integrating was discussed. Compared with several published approximate formulae, this new one is much superior to all other approximations and is the most suitable solution for the evaluation of kinetic parameters from TG experiments.

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Abstract  

A method is proposed for evaluation of the activation parameters for reactions which occur under non-isothermal conditions. This method can discriminate between possible differential conversion functions. The proposed method, which was coded into a software package available to the scientific community, is designed to solve an overdetermined systems of equations: dai/dt=k(Ti)f(ai) where i equations are to be considered (i can be the number of experimental points). Solution of this overdetermined system with a pseudo-inverse matrix method furnishes the activation parameters and the parameters of the conversion function f(a). Some examples of application of this method in non-isothermal kinetic analysis are presented.

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-isothermal kinetic models. In the present study, devolatilization non-isothermal kinetic analysis of agricultural stalks and application of TG-FT/IR analysis were investigated. Stalks of agricultural materials, sunflower, rice, corn, and wheat, are abundant in Edirne

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Abstract  

In this research, non-isothermal kinetics and feasibility study of medium grade crude oil is studied in the presence of a limestone matrix. Experiments were performed at a heating rate of 10°C min−1, whereas the air flow rate was kept constant at 50 mL min−1 in the temperature range of 20 to 600°C (DSC) and 20 to 900°C (TG). In combustion with air, three distinct reaction regions were identified in all crude oil/limestone mixtures, known as low temperature oxidation (LTO), fuel deposition (FD) and high temperature oxidation (HTO). The activation energy values were in the order of 5–9 kJ mol−1 in LTO region and 189–229 kJ mol−1 in HTO region. It was concluded that the medium grade crude oil field was not feasible for a self-sustained combustion process.

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Abstract

In the present study samples of Se100 − xSx has been prepared by conventional melt-quenching technique in the composition range 5 ≤ x ≤ 20 (at.%). The crystallization process in glassy system was investigated under non-isothermal condition using differential scanning calorimetry (DSC) at 5, 10, 15, and 20 °C/min heating rates (φ). The DSC traces have been analyzed in terms of activation energy (ΔE c) and Avrami exponent (n) using different models viz. the Starink, Flynn–Wall–Ozawa, the Friedman–Ozawa, Kissinger–Akahira–Sunose equations. The composition dependence on the glass transition temperature (T g), the crystallization temperature (T c), and the peak temperatures (T p) of the samples were also determined. The analysis shows that the incorporation of sulfur content has a strong influence on the crystallization mechanism for the Se–S glassy system.

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Abstract  

The mathematical evaluation of the activation energy, E, of non-isothermal degradation reactions is usually made using the Ozawa/Flynn–Wall isoconversion principle and involves the numerical resolution of a set of integrals without closed form solution, which are solved by polynomial approximation or by numeric integration. In the present work, the isoconversion principle, originally described and maintained until now as an algebraic problem, was written as a set of ordinary differential equations (ODEs). The individual ODEs obtained are integrated by numeric methods and are used to estimate the activation energy of simulated examples. A least square error (LSE) objective function using the introduced ODEs was written to deal with multiple heating rate CaCO3 thermal decomposition TG experiments.

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Abstract  

A new method is reported for the evaluation of non-isothermal kinetic data for various forms of the conversion function. The algorithm is based on a pseudo-inverse matrix method. A description of the algorithm and some calculation examples are presented.

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Summary  

The paper contains an analysis of the used of Diefallah's composite integral method of kinetic parameters evaluation. It is shown that the application of this method should be preceded by the application of an isoconversional method through which the dependence of the activation energy, E, on the conversion degree,a, should be established. If Edepends ona, Diefallah's composite integral method leads to erroneous results. If Edoes not depend ona, the true kinetic model should be comprised in the pre-established set of kinetic models. These observations were checked for two sets of non-isothermal data, namely: (a) the TG curves corresponding to the dehydration of CaC2O4H2O; (b) the TG curves corresponding to the thermal decomposition of polyvinyl chloride (PVC).

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Abstract  

The dependence of the frequency factor on the temperature (A=A 0 T m) has been examined and the errors involved in the activation energy calculated from some integral methods without considering such dependence have been estimated. Investigated integral methods are the Coats-Redfern method, the Gorbachev-Lee-Beck method, the Wanjun-Yuwen method and the Junmeng-Fusheng method. The results have shown that the error in the determination of the activation energy calculated ignoring the dependence of the frequency factor on the temperature can be rather large and it is dependent on x=E/RT and the exponent m.

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Abstract  

In this paper, a systematic analysis of the errors involved in the determination of the kinetic parameters (including the activation energy and frequency factor) from five integral methods has been carried out. The integral methods analyzed here are Coats-Redfern, Gorbachev, Wanjun-Yuwen-Hen-Zhiyong-Cunxin, Junmeng-Fusheng-Weiming-Fang, Junmeng-Fang and Junmeng-Fang-Weiming-Fusheng method. The results have shown that the precision of the kinetic parameters calculated by the different integral methods is dependent on u (E/RT), that is, on the activation energy and the average temperature of the process.

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