Authors:Mourad Ibrahim Daoudi, Abdelhafid Triki, and Abdelkrim Redjaimia
optimize the microstructure.
Phase transformations occur during both isothermal and non-isothermal annealing, involving several nucleation and growth mechanisms as summarized by Kempen et al. [ 1 ], for example. The most important kineticparameters
Studying the kinetics of isothermal decomposition
of thirteen selenites at isothermal heating, the values of activation energy E of the process, pre-exponential factor A in Arrhenius equation and changes of entropy for
the formation of the activated complex of the reagent were calculated. Direct
dependence between the thermal stability of the selenites and their cation
radii on their 'hardness' or 'softness' was found.
The dependence was interpreted in the terms of the generalized perturbation
theory of chemical reactivity. Kinetic compensation effect was observed only
for the selenites, which thermally decompose by the same mechanism.
Authors:Lunyu Qu, Ronghua Ma, Yaguang Chen, Yu Chen, and Chuntao Liu
The thermal properties of four heteropoly complexes α-K3H3[SiW11Ni(H2O)O39]·11.5H2O (I), α-K3H2[SiW11Fe(H2O)O39]·9H2O (II), α-[(C4H9)4N]3.5H1.5[SiW11Fe(H2O)O39]·4.5H2O (III) and α-[(C4H9)4N]3.5H2.5[SiW11Cu(H2O)O39]·6H2O (IV) were studied by means of TG, DTA and DSC. The activation energy and reaction order of the thermal decomposition reaction
of these complexes have been calculated.
The thermal behaviour of wool, untreated and chlorinated to various extents, was investigated. The kinetic parameters of the water loss and pyrolysis processes were computed and, based on their values, the way chlorination treatment affects wool fibre is discussed. As it appears, the chlorination process affects the fibre only superficially and not its internal chemical composition, as the values of the kinetic parameters of the thermal decomposition of wool fibre do not seem to be influenced at all by the treatment.
Three DTA peaks (two endo and one exothermic) were replotted in the form of ∑ peak area.Δa, or ∑ peak magnitude,ΔT, as a function of temperature. The integral sigmoid curves were plotted in the form of logg(α) vs. 1/T or log logg(α)/T2vs. 1/T. Both of the proposed summation methods gave satisfactory straight lines (F1 function), characterized by the same activation energies, correlation coefficients and standard deviations. Integration of the peak areas by Simpson's rule resulted in the same values as obtained by the summation procedure. Analysis by the suggested integral method resulted in activation energies that show a logarithmic divergence relative to the magnitude ofEa estimated directly from the DTA peaks.
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.