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Abstract  

The thermooxidative degradation of three models of oily soils was studied under non-isothermal conditions, at heating rates of 5, 10, 15 and 20�C min−1. Di-octyl-sebacate, as model for synthetic oil, was adsorbed on silica, alumina and silico-alumina, considered models for the inorganic micelle of a soil. For a kinetic analysis, the TG data were processed by three methods: Flynn-Wall-Ozawa, Friedman and NPK (Nomen-Sempere). The results indicate the NPK as the less speculative method that allows a separation of the elementary steps and at the same time a separation of the temperature, respective conversion dependent part of the reaction rate.

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Summary Due to the criticism of the non-isothermal kinetic at a single heating rate, in the last period, data obtained at different heating rates are processed by means of elevated methods like Friedman’s (FD) differential-isoconversional method or the one suggested by Budrugeac and Segal (BS). The non-parametric kinetics (NPK) method, suggested by Serra, Nomen and Sempere offers two major advantages: the possibility of separation of two or more steps of a complex decomposition reaction; and the possibility of discrimination between the conversion, with regard to the temperature functions of a rate equation. Comparative data of FD, BS and modified version of NPK method are presented for decomposition of three compounds used as polyisocyanate stabilizer.

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Abstract  

The example of the sequence of reactions

\documentclass{aastex} \usepackage{amsbsy} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{bm} \usepackage{mathrsfs} \usepackage{pifont} \usepackage{stmaryrd} \usepackage{textcomp} \usepackage{upgreek} \usepackage{portland,xspace} \usepackage{amsmath,amsxtra} \pagestyle{empty} \DeclareMathSizes{10}{9}{7}{6} \begin{document} $${\text{A}}\xrightarrow{{k_1 }}{\text{B}}\xrightarrow{{k_2 }}{\text{C}}$$ \end{document}
and the steady-state approximation are used to present a demonstration of the fact that the evolution of the reaction rates under non-isothermal conditions depends on the ratio of the activation energies and on the heating rate. At the same time, it is shown that, under isothermal conditions, the ratio of the activation energies plays no role.

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Abstract  

A new unsymmetrical solid Schiff base (LLi) was synthesized using L-lysine, o-vanillin and 2-hydroxy-l-naphthaldehyde. Solid lanthanum(III) complex of this ligand [LaL(NO3)]NO3·2H2O have been prepared and characterized by elemental analyses, IR, UV and molar conductance. The thermal decomposition kinetics of the complex for the second stage was studied under non-isothermal condition by TG and DTG methods. The kinetic equation may be expressed as: dα/dt=Ae−E/RT(1−α)2. The kinetic parameters (E, A), activation entropy ΔS # and activation free-energy ΔG # were also gained.

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Abstract  

Crystal of the complex Ni2L (ClO4)2 was obtained by reaction of Ni(ClO4)2 and macrocyclic ligand H2L, where L2– is the dinucleating macrocycle with two 2,6-di(aminomethyl)-4-methyl phenolate entities combined by the same two lateral chains, –(CH2)2–NH–(CH2)2–, at the amino nitrogens. The thermal decomposition processes of the title complex were studied in a dynamic atmosphere of dry argon using TG-DTG. The kinetic analysis of the first and second thermal decomposition steps were performed via the TG-DTG curves, and the kinetic parameters were obtained from analysis of the TG-DTG curves with integral and differential methods. The most probable kinetic function was suggested by comparison of the kinetic parameters.

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Abstract  

Three rational fraction approximations for the temperature integral have been proposed using the pattern search method. The validity of the new approximations has been tested by some numerical analyses. Compared with several published approximating formulas, the new approximations is more accurate than all approximations except the approximations proposed by Senum and Yang in the range of 5≤E/RT≤100. For low values of E/RT, the new approximations are superior to Senum-Yang approximations as solutions of the temperature integral.

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Abstract  

The influence of the specific surface area on the crystallization processes of two silica gels with different specific surface areas has been investigated in non-isothermal conditions using DTA technique. The activation energies of the crystallization processes were calculated using four isoconversional methods: Ozawa-Flynn-Wall, Kissinger-Akahira-Sunose, Starink and Tang. It has been established that, the decrease of the surface area from S=252.62 m2 g−1, in the case of sample GS2, to S=2.52 m2 g−1, in the case of sample GS1, has determined a slight increase of the activation energy of the crystallization process of the gels. Regardless of the isoconversional method used, the activation energy (E α) decreases monotonously with the crystallized fraction (α), which confirms the complex mechanism of gels crystallization. It has been proved that the Johnson-Mehl-Avrami model cannot be applied for the crystallization processes of the studied silica gels.

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