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.
A thermogravimetric method is proposed for study of the kinetic parameters of coked HZSM-5 zeolite regeneration. The technique,
which makes use of integral thermogravimetric curves, was optimized by microprocessed integrated mathematical methods. The
kinetic parameters obtained from the TG curves are the activation energy, the rate constants, the half-life times, and in
particular the coke removal time as a function of temperature. The activation energy calculated by using the Flynn and Wall
kinetic method was 81.4 kJ mol−1. It was observed that, to remove 99% of the coke from the zeolite in a period of 1 h, it would be necessary to carry out
thermo-oxidation at 748 K, with a dry air purge flow of 120 cm3 min−1.
Authors:J. Straszko, M. Olszak-Humienik, and J. Możejko
Thermogravimetry (TG-DTG), and differential thermal analysis (DTA) were used in the study of the kinetics of decomposition
of cobalt sulphate hexahydrate under an air atmosphere.
The kinetics of the particular stages of CoSO4 6H2 O decomposition were evaluated from the dynamic mass loss data. The values of the kinetic parameters for each stage of the
thermal decomposition were calculated from the α(T) data by using the integral method, applying the Coats-Redfern approximation.
A simple method of determination of kinetic parameters by analysis of DTA(t) function was developed for the case of systems undergoing transitions without mass change and when kinetic equation describing
transition rate is known. The presented method also permits the determination of transition rate dα/dt (or α(t )) when the kinetic equation of transition is unknown. The developed method was tested using DTA data of crystallization
of 2CaOAl2 O3 1.95SiO2 glass pure and doped with Cr3+ and Nd3+ .
Separate stages of mathematical processing of thermogravimetric data, the difficulties most often encountered, and typical error sources are considered. A complex procedure of automatic acquisition and editing of experimental data, including calculation of effective kinetic parameters, is described and an appropriate algorithm for the 15 BCM-5 microcomputer is presented. The computer calculation of the kinetic parameters of the multistage thermal decomposition of a polyamide fibre is given as an example.
This article describes synthesis and route of thermal degradation and studies of kinetic parameters of some coordination polymers
of first transition series metal ions viz. Mn(II), Co(II), Ni(II), Cu(II), and Zn(II). The newly synthesized ligand and its
coordination polymers have been characterized by various instrumental techniques. The thermal degradation studies have been
studied at different heating rates to determine the apparent activation energy, order of reaction, entropy change, free energy
change, apparent entropy change, and frequency factor using Sharp–Wentworth and Freeman–Carroll methods. Thermo gravimetric
analysis (TGA) has been used to determine the thermal stability of coordination polymers. The decomposition temperatures of
the polymers were defined by half decomposition curve technique.
Authors:J. Escribano, R. Masegosa, D. Nava, M. Prolongo, and Catalina Salom
The curing of the neat
unsaturated polyester resin (UP) with benzoyl peroxide (initiator) as well
as the curing of UP modified with two poly(ε-caprolactone) PCL samples
(PCL2 and PCL50) of different molecular masses (Mn=2⋅103
respectively), were investigated by non-isothermal differential scanning calorimetry
(DSC), at different heating rates. The activation energy was determined from
the variation of the peak exotherm temperature, Tpeak,
upon heating rate. Besides, the degree of conversion (α) was obtained
from isothermal DSC measurements at 80°C at different curing times for
neat UP, UP+ PCL2 and UP+PCL50. Kinetic parameters were deduced assuming the nth order reaction kinetic
model for neat UP, UP+PCL2 and UP+PCL50 systems.
The possibility to determine the kinetic parameters for temperature programmed reduction of Cu/Fe3O4 using only one TPR profile is analyzed. The same data are analyzed both by Friedman’s iso-conversional method and another
one previously derived and published by the authors. One shows that taking into account the experimental restrictions of Monti
and Baiker, the Friedman’s method, although gives values of the activation energy smaller than the real values, indicates
a very similar dependence of these on the reduction degree. On the basis of some synthetic data one shows that the errors
are very large when these recommendations are neglected, being possible to determine a false dependence on the degree of reduction.
The derivatographic method was used for the quantitative determination of water content in selected flour and fat products.
Weight losses and thermal effects taking place in the examined products under the influence of heat were read from the obtained
derivatograms. Percentage water contents were calculated from TG curves within the range from 5.6% (rice cereal) to 16.0%
(potato flour), based on the diagrams recorded within the temperature range 20–1000C, narrower temperature ranges of dehydration
and decomposition processes were determined. In addition, the number of stages of thermal decomposition of the examined products
was determined and appropriate kinetic parameters were calculated.
The values of the activation energy (Ea) of dehydration, frequency factor (A) and reaction order (n) were calculated from TG, DTG andT curves within the temperature range from 20 to 90C. For potato flour the following values were obtained:Ea=27.825 kJ/mol,A=1.05105 1/s andn=2.9710−3, for the remaining samples under investigation the activation energyEa is several dozen kJ/mol and the reaction ordern is very low. The obtained data show that the dehydration process under study is mainly associated with evaporation of water
adsorbed on products and to less extent with chemical processes.
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.