For the most common kinetic models used in heterogeneous reactions, the dependencies on xm = E/RTm (E is the activation energy, Tm is the temperature corresponding to maximum process rate, R is the gas constant) on the relative errors (e%) in the determination of the activation energy from the slope of the Kissinger straight line ln(β / Tm2) vs. 1/Tm (β is the heating rate) are evaluated. It is pointed out that, for xm≥10.7 and all kinetic models, ∣e%∣≤5%. Some possible cases exhibiting high values of ∣e%∣, which can be higher than 10%, are put in evidence and discussed.
Authors:A. Cadenato, J. Morancho, X. Fernández-Francos, J. Salla, and X. Ramis
The thermal polymerization kinetics of dimethacrylate monomers was studied by differential calorimetry using non-isothermal
experiments. The kinetic analysis compared the following procedures: isoconversional method (model-free method), reduced master
curves, the isokinetic relationship (IKR), the invariant kinetic parameters (IKP) method, the Coats-Redfern method and composite
integral method I. Although the study focused on the integral methods, we compared them to differential methods. We saw that
even relatively complex processes (in which the variations in the kinetic parameters were only slight) can be described reasonably
well using a single kinetic model, so long as the mean value of the activation energy is known (E). It is also shown the usefulness of isoconversional kinetic methods, which provide with reliable kinetic information suitable
for adequately choosing the kinetic model which best describes the curing process. For the system studied, we obtained the
following kinetic triplet: f(α)=α0.6(1−α)2.4, E=120.9 kJ mol−1 and lnA=38.28 min−1.
Authors:P. Budrugeac, Alice Luminita Petre, and E. Segal
The validity of isoconversional methods used to evaluate the activation energy is discussed. The authors have shown that the Flynn-Wall-Ozawa and Friedman methods give results that agree with each other only if the activation energy does not change with the degree of conversion. A criterion for the reaction mechanism as expressed by the differential conversion function is suggested too.
Authors:Gabriela Vlase, T. Vlase, Ramona Tudose, Otilia Costişor, and N. Doca
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.
Authors:Y. Fan, Z. Gao, C. Bi, S. Xie, and X. Zhang
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.
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.
Authors:J. Zsakó, I. Ganescu, Cs. Várhelyi, and L. Chirigiu
Thermal decomposition of 6 complexes of the type AH[Cr(NCS)4 (am)2]· nH2O is studied with derivatograph. The formation of Cr(NCS)3 as a labile intermediate is presumed. For some decomposition stages kinetic parameters are derived. The kinetic compensation effect is discussed.
Authors:Alexandra Ioiţescu, Gabriela Vlase, T. Vlase, and N. Doca
The kinetics of thermal decomposition
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.
The condensation approximation (CA) and numerical regularization procedure (RP) methods used to solve a Fredholm integral
equation of the first kind describing the adsorption equilibria on a heterogeneous solid surface under isothermal conditions
have been adopted in the present study to evaluate desorption energy distributions from temperature-programmed desorption
(TPD) spectra. From comparisons of the computational results obtained by means of these methods on the basis of simulated
TPD spectra, it follows that the CA gives stable solutions for wide desorption energy distributions and it can be used successfully
for calculations from wide and clear resolved peaks in the TPD spectra. The use of the RP is more advantageous for acquisition
of the distributions from closely related narrow peaks in the TPD spectra.
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.