Search Results

You are looking at 81 - 90 of 206 items for :

  • "non-isothermal kinetics" x
  • Refine by Access: All Content x
Clear All

Abstract  

Kinetics of thermal decomposition of three structurally similar complexes Co2Cu(C2O4)3 (R-diam)2, where R is ethyl, 1,2-propyl or 1,3-propyl, was studied under non-isothermal conditions and nitrogen dynamic atmosphere at heating rates of 5, 7, 10, 12 and 15 K min−1. For data processing the Flynn-Wall-Ozawa and a modified non-parametric kinetic methods were used. By both methods the activation energy are in the range of 97–102 kJ mol−1. The formal kinetic is r=kα(1−α)2. Also a compensation effect between lnA and E was evidenced. The kinetic analysis lead to the conclusion of an identic decomposition mechanism by a single step process.

Restricted access

Abstract  

The kinetics of thermal decomposition of Ca(H2PO4)2H2O under non-isothermal conditions was studied. The TG/DTG curves were obtained at five heating rates: 5, 7, 10, 12 and 20 K min–1. The kinetic analysis was performed by means of three methods: Friedman, Budrugeac–Segal and NPK by Sempere and Nomen. An important dependence of the activation energy vs. the conversion degree was observed and also a compensation effect. The decomposition consists of water loss and is due to the elimination of crystallization water and an intermolecular condensation, respectively.

Restricted access

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.

Restricted access

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.

Restricted access

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.

Restricted access

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.

Restricted access

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.

Restricted access