The following problems concerning the apparent compensation effect (CE) (lnA=a+bE, where A is the pre-exponential factor, E is the activation energy, a and b are CE parameters) due to the change of the conversion function and on which the invariant kinetic parameters method (IKP
method) is based, are discussed: (1) the explanation of this kind of CE; (2) the choice of the set of conversion functions
that checks CE relationship; (3) the dependencies of CE parameters on the heating rate and the temperature corresponding to
the maximum reaction rate. Using the condition of maximum of the reaction rate suggested by Kissinger (Kissinger law), it
is pointed out that, for a certain heating rate, the CE relationship is checked only for reaction order (Fn) and Avrami-Erofeev
(An) kinetic models, and not for diffusion kinetic models (Dn). Consequently, IKP method, which is based on the supercorrelation
relationship between CE parameters, can be applied only for the set Fn+ An of kinetic models.
The dependencies of a and b parameters on the heating rate and Tm (temperature corresponding to maximum reaction rate) are derived.
The theoretical results are discussed and checked for (a) TG simulated data for a single first order reaction; (b) TG data
for PVC degradation; (b) the dehydration of CaC2O4·H2O.
Authors:A. Rotaru, Anca Moanţă, P. Rotaru, and E. Segal
Thermal analysis of 4-[(4-chlorobenzyl)oxy]-4′-chloro-azobenzene dye, exhibiting liquid crystalline properties, was performed
in dynamic air atmosphere. The compound behavior was investigated using TG, DTG, DTA and DSC techniques, under non-isothermal
linear regime. The evolved gases were analyzed by FTIR spectroscopy. Kinetic parameters of the first decomposition step were
obtained by means of multi-heating rates methods, such as isoconversioanl methods, IKP method and Perez-Maqueda et al. criterion.
Advanced software (TKS-SP2.0 version) for thermal and kinetic analysis, for determining the non-isothermal kinetic parameters
of heterogeneous processes has been developed. The dynamic handle of conversion degree steps and ranges, heating rates and
kinetic models, makes the evaluation of the kinetic parameters much faster, for TG, TPR and dilatometry experiments. The standard
procedure for evaluating the kinetic triplet was implemented; several linear isoconversional methods (from generalized KAS
to FWO, Li-Tang and Friedmann methods), IKP method, Perez-Maqueda et al. criterion (both by Differential equation) and Master plots method. The software is designed mainly for data processing of
experimental files, but may also import other already transformed numeric data.
A software package to determine the non-isothermal kinetic parameters of heterogeneous reactions has been developed. The dynamic
handle of conversion degree step and ranges, heating rates and kinetic models makes the evaluation of the activation parameters
much faster. The standard procedure: ‘model-free’ kineitc, IKP and Perez-Maqueda et al. methods, is applied for the determination of the kinetic triplet corresponding to thermal induced transformations. The software
is designed mainly for thermogravimetric, temperature programmed reduction and dilatometry data processing, but may also import
already transformed numeric data.
Authors:A. Rotaru, Anca Moanţă, Gina Popa, P. Rotaru, and E. Segal
Thermal analysis of 2-allyl-4-((4-(4-methylbenzyloxy)phenyl)diazenyl)phenol dye was performed in air flow. The compound thermal behavior was investigated using TG, DTG and DSC techniques, under non-isothermal linear regime. Kinetic
parameters of the two decomposition steps were obtained by means of multi-heating rates methods. Isoconversioanl methods (KAS
and FWO), Invariant Kinetic Parameters method and Perez-Maqueda et al. criterion (by means of CR and FW equations) were used.
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: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.
Authors:C. Popescu, W. P. C. de Klerk, and E. L. M. Krabbendam-LaHaye
Summary Gun propellants are per definition instable substances. During their lifetime a slow decomposition process is going-on. During this decomposition process the heat that is generated accelerates the process, which could result to an unsafe situation, or an unexpected explosion of the material. The temperature to initiate the explosion of a propellant is of importance for the storage conditions of such a substance. The method used so far to evaluate this temperature is based on an extrapolation of the Kissinger equation at zero heating rate. A new proposal is the use of the invariant kinetic parameters (IKP) method to determine the iso-kinetic temperature and extrapolating it to zero heating rate as an alternative method. The results are discussed for some examples.
The non-isothermal decomposition process of the powder sample of palladium acetylacetonate [Pd(acac)2] was investigated by thermogravimetric (TG) and the X-ray diffraction (XRD) techniques. Model-free isoconversional method
of Tang, applied to the investigated decomposition process, yield practically constant apparent activation energy in the range
of 0.05≤α≤0.95. It was established, that the Coats-Redfern (CR) method gives several statistically equivalent reaction models,
but only for the phase-boundary reaction models (R2 and R3), the calculated value of the apparent activation energy (E) is nearest to the values of E obtained by the Tang’s and Kissinger’s methods.
The apparent activation energy value obtained by the IKP method (132.4 kJ mol−1) displays a good agreement with the value of E obtained using the model-free analysis (130.3 kJ mol−1). The artificial isokinetic relationship (aIKR) was used for the numerical reconstruction of the experimental integral model
function, g(α). It was established that the numerically reconstructed experimental function follows R3 reaction model in the range of
α, taken from model-free analysis. Generally, decomposition process of Pd(acac)2 starts with initial nucleation which was characterized by rapid onset of an acceleratory reaction without presence of induction
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.