A kinetic study of the crystallization of poly(ethylene oxide) (PEO) and of a blend of PEO+poly(bisphenol A-co-epichlorohydrin)
(PBE) was performed by using DSC in a non-isothermal program at constant cooling rates. The curves obtained were analyzed
by the Kissinger, Ozawa and Friedman methods, with determination of the kinetic parameters in each case. As a consequence
of the presence of PBE, the kinetic parameters were altered, leading to the conclusion that PBE has some influence on the
crystallization of PEO, modifying its mechanism.
There are many reactions of interest in which one or more of the reactants belong to some solid phases. Modern thermoanalytical instruments can conveniently provide reaction kinetic data of high precision and accuracy, from which the underlying activation energyE may be derived in principle. Unfortunately, no ‘best' method yet exists for the derivation when the data have been collected with a programmed linear increase in sample temperature, unlike the case of isothermal measurements, which however suffer from experimental limitations . Here we propose a method for extractingE from non-isothermal data, that promises general validity.
A differential isoconversional non-linear procedure for evaluating activation energy from non-isothermal data is suggested.
This procedure was applied to model reactions (simulations) and to the dehydration of CaC2O4⋅H2O. The results were compared with those obtained by other isoconversional methods.
Authors:C. Ribeiro, W. de Souza, Marisa Crespi, J. Gomes Neto, and F. Fertonani
Tungsten carbide, WC, has shown dissimilar thermal behavior when it is heated on changeable heating rate and flow of oxidant
atmosphere. The oxidation of WC to WO3 tends to be in a single and slow kinetic step on slow heating rate and/or low flux of air. Kinetic parameters, on non-isothermal
condition, could be evaluated to the oxidation of WC to heating rate below 15°C min−1 or low flow of air (10 mL min−1). The reaction is governed by nucleation and growth at 5 to 10°C min−1 then the tendency is to be autocatalytic, JMA and SB, respectively.
Authors:M. Badea, R. Olar, E. Cristurean, D. Marinescu, A. Emandi, P. Budrugeac, and E. Segal
This paper deals with the investigation concerning the thermal stability of two new azo-derivatives and their Cu(II) complexes
of type [Cu(L1)2] and, respectively, ((C4H9)4N)2[Cu(L2)2]. The thermal decomposition steps have been put in evidence. For the kinetically workable ones, the values of the activation
energy vs. conversion degree were determined.
A model describing the roles of bound and unbound vacancies is proposed in order to predict defect decay and short-range-order
kinetics of quenched binary alloys during linear heating experiments. This is an alternative treatment of a previous approach.
The model has been applied to the differential scanning calorimetry (DSC) curves of Cu-5 at.% Zn quenched from different temperatures.
An expression to calculate the activation energy for migration of solute-vacancy complexes was also developed which make use
of DSC trace data. A value of 89.120.32 kJ mol-1 was obtained for the above alloy. The relative contribution of bound and unbound vacancies to partition of effective activation
energy corresponding to the ordering process as influenced by quenching temperature was also assessed.
Authors:J. Zhang, L. Ge, X. Zhang, Y. Dai, H. Chen, and L. Mo
The thermal decomposition of Zn[NFA]2
5H2O (NFA=C16H18FN3O3, norfloxacin) and its kinetics were studied under non-isothermal conditions in air by TG-DTG and DTA methods. The intermediate and residue for each decomposition were identified from the TG curve. The non-isothermal kinetic data were analyzed by means of the Achar method and the Madhusudanan-Krishnan-Ninan (MKN) method. The possible reaction mechanisms were investigated by comparing the kinetic parameters. The kinetic equation for the second stage can be expressed as d/dt=Aexp(–E/RT)(1–).
Authors:T. Vlase, Gabriela Vlase, Nicoleta Birta, and N. Doca
A comparative kinetic analysis on the thermal decomposition of tartaric acid and potassium tartrate under non-isothermal conditions
was performed. The non-isothermal kinetic parameters were determined by the following four methods: integral isoconversional
method suggested by Flynn-Wall-Ozawa (FWO method); differential isoconversional method suggested by Friedman; Budrugeac-Segal
method and Non-Parametric-Kinetic (NKP) method suggested by Sempere and Nomen and modified by Vlase and Doca. The comparison
of the results obtaining by these methods leads to interesting conclusions. The experimental data were obtained in dynamic
nitrogen atmosphere at heating rates of 5, 7, 10, 12 and 15 K min−1. The less speculative kinetic analysis was possible by the NPK method.
Authors:T. Vlase, N. Doca, Gabriela Vlase, C. Bolcu, and F. Borcan
In the present work a comparative kinetic study was performed on the thermal behavior of three antioxidants of IRGANOX-type
(L101, L109 and L115) in dynamic air atmosphere under non-isothermal conditions.
The TG-DTG data were obtained at heating rates of 5, 7, 10 and 15 K min−1. The kinetic parameters were obtained by processing these data with strategies corresponding to Flynn-Wall-Ozava (FWO), Friedman
(FR), Budrugeac-Segal (BS) and non-parametric kinetic (NPK) methods.
The thermal degradation by all the three compounds take place in melted state, so that any kinetic models regarding the decomposition
of solids are inapplicable. Only with the NPK method it was possible a separation between the two functions of the reaction
For the temperature dependence, f(T), an Arrhenius-type model was searched; for the conversion dependence, the Ŝestak-Berggren equation was suggested in order
to discriminate between physical (m) and chemical (n or p) steps of a complex thermodegradation process.
Authors:Loredana Feher, B. Jurconi, Gabriela Vlase, T. Vlase, and N. Doca
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.