Authors:C. Păcurariu, R. Lazău, I. Lazău, R. Ianoş, and B. Tiţa
The crystallization mechanism of the glass-ceramics obtained from Romanian (Şanoviţa) basalt in the presence of 3 and 5% CaF2 as nucleation agent has been investigated under non-isothermal conditions using DTA technique. The activation energies of
the crystallization processes were calculated using the Kissinger-Akahira-Sunose, Ozawa-Flynn-Wall, Starink and Tang isoconversional
methods. The monotonous decreases in the activation energy (Ea) with the crystallized fraction (α) confirms the complex mechanism of the glass-ceramics crystallization process. It has
been proved that the Johnson-Mehl-Avrami model cannot be applied for the studied glass-ceramics crystallization process.
Authors:N. Doca, Gabriela Vlase, T. Vlase, and G. Ilia
The thermal behavior of Cd2+ and Co2+ phenyl-vinyl-phosphonates was studied using two different experimental strategies: the coupled TG-EGA (FTIR) technique by
decomposition in nitrogen respectively air, and the kinetic analysis of TG data obtained in dynamic air atmosphere at four
heating rates. In nitrogen two decomposition steps were observed: the loss of crystallization water, respectively the decomposition
of the phenyl-vinyl radical. In air, the same dehydration was observed as the first step, but the second one is a thermooxidation
of the organic radical with formation of the pyrophosphoric anion.
The kinetic analysis of the TG non-isothermal data was performed by the isoconversional methods suggested by Friedman and
Flynn, Wall and Ozawa, as well as by the non-parametric (Sempere-Nomen) method. All processes put in evidence in TG curves
exhibit strong changes of the activation energy values with the conversion degree, which mean that these processes are complex
ones. Assuming that each of these processes consists in two steps, the application of non-parametric method leads to average
values of the activation energy close to the average values of this parameter obtained by isoconversional methods.
The paper presents a non-isothermal kinetic study of the decomposition of Zn acetate-based gel precursors for ZnO thin films,
based on the thermogravimetric (TG) data. The evaluation of the dependence of the activation energy (E) on the mass loss (Δm) using the isoconversional methods (Friedman (FR), Flynn-Wall-Ozawa (FWO) and Kissinger-Akahira-Sunose (KAS)) has been presented
in a previous paper. It was obtained that the sample dried at 125°C for 8 h exhibits the activation energy independent on
the heating rate for the second decomposition step. In this paper the invariant kinetic parameter (IKP) method is used for
evaluating the invariant activation parameters, which were used for numerically evaluation of the function of conversion.
The value of the invariant activation energy is in a good agreement with those determined by isoconversional methods. In order
to determine the kinetic model, IKP method was associated with the criterion of coincidence of the kinetic parameters for
all heating rates. Finally, the following kinetic triplet was obtained: E=91.7 (±0.1) kJ mol−1, lnA(s−1)=16.174 (±0.020) and F1 kinetic model.
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:B. Tiţa, Eleonora Marian, D. Tiţa, Gabriela Vlase, N. Doca, and T. Vlase
Thermal analysis is one of the most widely used methods for studying the solid state of pharmaceutical substances.
TG/DTG and DSC curves provide important information regarding the physical properties of the pharmaceutical compounds (stability,
compatibility, polymorphism, kinetic analysis, phase transitions etc.).
The purpose of a kinetic investigation is to calculate the kinetic parameters and the kinetic model for the studied process.
The results are further used to predict the system’s behaviour in various circumstances.
A kinetic study regarding the diazepam, nitrazepam and oxazepam thermal decomposition was performed, under non-isothermal
and isothermal conditions and in a nitrogen atmosphere, for the temperature steps: 483, 498, 523, 538 and 553 K. The TG/DTG
data were processed by three methods: isothermal model-fitting, Friedman’s isothermal-isoconversional and Nomen-Sempere non-parametric
In the model-fitting methods the kinetic triplets (f(α), A and Ea) that defines a single reaction step resulted in being at variance with the multi-step nature of diazepines decomposition.
The model-free approach represented by isothermal and non-isothermal isoconversional methods, gave dependences of the activation
energies on the extent of conversion.
It is very difficult to obtain an accord with the similar data which resulted under non-isothermal conditions from a previous
The careful treatment of the kinetic parameters obtained in different thermal conditions was confirmed to be necessary, as
well as a different strategy of experimental data processing.
Authors:S. De Angelis Curtis, Krystyna Kurdziel, S. Materazzi, and S. Vecchio
The crystal structure of a manganese(II) 1-allylimidazole complex ([Mn(1-AIm)3(NO3)2], where 1-Aim=1-allylimidazole), was characterized by X-ray diffraction (XRD) using SHELX-97. The thermal behaviour of the
complex was investigated by thermogravimetry (TG) coupled with an FTIR unit. The complex showed a multi-step decomposition
related to the release of the ligand molecules, followed by oxidation. The final residue at 1073 K was found to be manganese(II)
oxide. Evolved gas analysis allowed to prove the oxidative decomposition pattern of the examined complex, initially proposed
by the percentage mass loss data. Finally, a kinetic analysis of the oxidative decomposition steps was made using the Kissinger
equation, while the complex nature of the decomposition kinetics was revealed by the isoconversional Ozawa-Flynn-Wall method.
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 activation energies of the same process are often reported to have different values, which are usually explained by the
differences in experimental conditions and sample characteristics. In addition to this type of uncertainty, which is associated
with the process (ΔEprocess) there is an uncertainty related to the method of computation of the activation energy (ΔEmethod). For a method that uses fitting single heating rate data to various reaction models, the value of ΔEmethod) method is large enough to explain significant differences in the reported values of the activation energy. This uncertainty
is significantly reduced by using multiple heating rate isoconversional methods, which may be recommended for obtaining reference
values for the activation energy.
The thermal degradation of polymers has been studied quite extensively using thermogravimetric measurements. For the kinetic
description, most of the times single rate heating data and model-fitting methods have been used. Since the thermal degradation
of the polymers is a very complex reaction, the choice of a reliable model or a combination of kinetic models is very important.
The advantages or the disadvantages of using a single heating rate or multiple heating rates data for the determination of
the kinetic triplet have been investigated. Also, the activation energy has been calculated with the isoconversional and model-fitting
methods. The reaction model was determined with the model-fitting method. The limits of all these procedures were investigated
with experimental data of the thermal degradation of the poly(ethylene adipate) (PEAd).
The thermal decomposition of three new reagent cyclohexylamine-p-tolylglyoxime (L1H2), tertiarybutyl amine-p-tolylglyoxime (L2H2) and secondary butylamine-p-tolylglyoxime (L3H2 and their Co-complexes were studied by both isothermal and nonisothermal methods. As expected, the complex structure of Co-complexes,
different steps with different activation energies were realized in decomposition process. Model-fitting and model-free kinetic
approaches were applied to nonisothermal and isothermal data. The kinetic triplet (f(α), A and E) related to nonisothermal model-fitting method can not be meaningfully compared with values obtained from isothermal method.
The complex nature of the multi-step process of the studied compounds was more easily revealed using a wider temperature range
in nonisothermal isoconversional method.