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:Oana Cătălina Mocioiu, Maria Zaharescu, Georgeta Jitianu, and P. Budrugeac
Two integral isoconversional methods (Flynn–Wall–Ozawa and
Kissinger–Akahira–Sunose) and the invariant kinetic parameters
method (IKP) were used in order to examine the kinetics of the non-isothermal
crystallisation of a silica-soda-lead glass. The objective of the paper is
to show the usefulness of the IKP method to determine both the activation
parameters and the kinetic model of the investigated process. Thismethod associated
with the criterion of coincidence of kinetic parameters for all heating rates
and some procedures of the evaluation of the parameter from Johnson–Mehl–Avrami–Erofeev–Kolmogorov
(JMAEK) equation led us to the following kinetic triplet: activation energy, E=170.5±2.5 kJ mol–1
, pre-exponential factor, A=1.178±0.350·10
10 min–1 and JMAEK model (Am) m=1.5.
The paper contains an analysis of the used of Diefallah's composite integral method of kinetic parameters evaluation. It is
shown that the application of this method should be preceded by the application of an isoconversional method through which
the dependence of the activation energy, E, on the conversion degree,a,
should be established. If Edepends ona, Diefallah's composite integral
method leads to erroneous results. If Edoes not depend ona, the
true kinetic model should be comprised in the pre-established set of kinetic models. These observations were checked for two
sets of non-isothermal data, namely: (a) the TG curves corresponding to the dehydration of CaC2O4H2O; (b) the TG curves corresponding to the thermal decomposition of polyvinyl chloride (PVC).
The accuracy of the newly proposed approximation is tested by numerical analyses. Compared with other existed approximations
for the general temperature integral, the new approximation is significantly more accurate than other approximations.
Thermal investigation has allowed us to show the changes undergone by a sort of nitrile-butadiene rubber (NBR) as a consequence ofγ-radiation-induced ageing. The parameters of the processes, which occur at progressive heating of the
investigated samples, were determined. It was shown that for γ-irradiated samples the activation parameters corresponding
to the thermo-oxidative process leading to solid products are correlated through the relation of compensation effect. Also,
it was shown that, by γ-irradiation, NBR undergoes a relatively rapid change of its thermal behaviour which can be due to
Authors:B. Zhou, S. Jiang, L. Zou, X. Wang, D. Wang, J. Liu, S. Shang, and D. Zhou
A new compound cyclohexyl-t-butyldimethylammonium tetraphenylborate, [C6H11N(CH3)2(C(CH3)3)]BPh4 has been prepared, and its decomposition mechanism was studied by TG. The IR spectra of the products of thermal decomposition were examined at every stage. Kinetic analysis for the first stage of thermal decomposition process was obtained by TG and DTG curves, and kinetic parameters were obtained from the analysis of the TG-DTG curves with integral and differential equations. The most probable kinetic function was suggested by comparison of kinetic parameters.
Authors:M. Badea, R. Olar, E. Cristurean, D. Marinescu, M. Brezeanu, M. Balasoiu, and E. Segal
This paper reports an investigation of the thermal stabilities of the class of coordination compounds containing lanthanide ions Ln(III) (Ln=La, Sm, Eu, Dy, Er), Co(II) ions and oxalate anions C2O
. The thermal decomposition steps were identified, and in some cases the values of the non-isothermal kinetic parameters were determined.
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–).
Results obtained on the thermooxidative degradations of LDPE (low-density polyethylene) and NBR (nitrile-butadiene rubber)
are presented. The activation energies for the thermooxidations leading to solid products were estimated. For LDPE, the activation
energies obtained from non-isothermal data are in satisfactory agreement with those obtained from isothermal data. For NBR,
the isothermal activation energy is ≉16% higher than the non-isothermal one. This difference is due to the morphological changes
undergone by NBR during its heating at the rather high temperatures at which isothermal measurements were performed.