Solid bisphenol-A epoxy
resin of medium molecular mass was cured using a Lewis acid initiator (ytterbium(III)
trifluoromethanesulfonate) in three different proportions (0.5, 1 and 2 phr).
A kinetic study was performed in a differential scanning calorimeter. The
complete kinetic triplet was determined (activation energy, pre-exponential
factor, and integral function of the degree of conversion) for each system.
A kinetic analysis was performed with an integral isoconversional procedure
(free model), and the kinetic model was determined both with the Coats-Redfern
method (the obtained isoconversional value being accepted as the effective
activation energy) and through the compensation effect. All the systems followed
the same isothermal curing model simulated from non-isothermal ones. The growth-of-nuclei
Avrami kinetic model A3/2 has been proposed as the
polymerization kinetic model. The addition of initiator accelerated the reaction
especially when 2 phr was added. 0.5 and 1 phr showed very few kinetic differences
This work is a study, by simultaneous thermogravimetry (TG) and differential thermal analysis (DTA), of the oxidation of a
water resistant aluminum nitride powder which has a special protective coating, and an uncoated AlN powder which has become
partially hydrated during its use. The activation energy for oxidation is estimated by the Kissinger and isoconversional methods.
In the former method, the temperatures of the oxidation peaks were obtained from DTA and DTG curves. The activation energies
for oxidation of the water resistant AlN, obtained by the Kissinger method, are 35710 kJ mol–1, 39212 kJ mol–1 using respectively DTG and DTA data. For the uncoated AlN, the values are 2437 and 2578 kJ mol–1, respectively. By the isoconversional method, the average values obtained for coated and uncoated samples are, respectively,
32310 and 2247 kJ mol–1. Therefore, the special coating, which protects the aluminum nitride from humidity action, also provides a higher resistance
Authors:C. Păcurariu, R. Lazău, I. Lazău, R. Ianoş, and T. Vlase
The influence of the specific surface area on the crystallization processes of two silica gels with different specific surface
areas has been investigated in non-isothermal conditions using DTA technique. The activation energies of the crystallization
processes were calculated using four isoconversional methods: Ozawa-Flynn-Wall, Kissinger-Akahira-Sunose, Starink and Tang.
It has been established that, the decrease of the surface area from S=252.62 m2 g−1, in the case of sample GS2, to S=2.52 m2 g−1, in the case of sample GS1, has determined a slight increase of the activation energy of the crystallization process of the
gels. Regardless of the isoconversional method used, the activation energy (Eα) decreases monotonously with the crystallized fraction (α), which confirms the complex mechanism of gels crystallization.
It has been proved that the Johnson-Mehl-Avrami model cannot be applied for the crystallization processes of the studied silica
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:Pratibha Srivastava, Inder Kapoor, Gurdip Singh, and Roland Fröhlich
Phenylenediammonium dibromide (PDADBr) salts have been prepared and characterized by X-ray crystallography. The thermal decomposition
of PDADBr has been studied by thermogravimetry (TG) and differential thermal analysis (DTA). Kinetic parameters have been
evaluated using model fitting and isoconversional methods. The thermolytic pathways have also been suggested which involve
proton transfer as a primary step to regenerate parent amine and HBr. Interaction between amine and HBr at higher temperature
yields gaseous products.
Kinetics of exothermal decomposition of 2-nitrophenylhydrazine (2-NPH) and 4-nitrophenylhydrazine (4-NPH) was investigated
by differential scanning calorimetry. The isoconversional methods, Friedman and Flynn-Wall-Ozawa, were applied to determine
the activation parameters from the common analysis of multiple curves measured at different heating rates. For the processes
involving two-step reactions the multivariate non-linear regression was used. A good agreement between the experimental and
the fitted data was found.
Authors:P. Budrugeac, J. Criado, F. Gotor, C. Popescu, and E. Segal
The isoconversional methods (Friedman and Flynn-Wall-Ozawa) as well as the invariant kinetic parameters method (IKP) were
used in order to work the TG data corresponding to the thermal dissociation of smithsonite. As a result we mention a mechanism
change at T≈671 K. For T>671 K, which corresponds to heating rates in the range 0.57– 8.06 K min–1, a reaction order model with 1<n≤1.4 describes the experimental data.
Authors:J. Suñol, J. Saurina, R. Berlanga, D. Herreros, P. Pagès, and F. Carrasco
A crystallization kinetics analysis of several polypropylene-polyethylene (PP-PE), PP-rich copolymers was made by means of
differential scanning calorimetry. The crystallization was studied via calorimetric measurements at different cooling rates.
Several additives were added to the base material. Some test samples were subjected to artificial ageing processes. A modified
isoconversional method was used to describe the crystallization process under non-isothermal conditions. The value of the
Avrami parameter was determined for primary and secondary crystallization.
Authors:S. Arias, M. Prieto, B. Ramajo, A. Espina, and J. García
The evaporation of octanoic (caprylic) acid was investigated by means of thermogravimetric analysis (temperature range: 300–600 K)
under a nitrogen dynamic atmosphere (heating rates: 0.16, 0.31, 0.63, 1.25, 2.5, 5 and 10 K min−1). Kinetic plots for a zero-order process were constructed based on the Arrhenius equation. The activation energy for the
evaporation process was calculated via both the Arrhenius plot and Vyazovkin’s isoconversional model-free method.
Authors:Marta Otero, X. Gómez, A. García, and A. Morán
The combustion of two different sewage sludges and a semianthracite coal was studied and compared by thermogravimetric analysis.
Non-isothermal thermogravimetric data were used to evaluate the Arrhenius parameters (activation energy and the pre-exponential
factor) of the combustion of these carbonaceous materials. The paper reports on the application of model-free isoconversional
methods for evaluating and comparing the corresponding activation energy of the combustion process.