The thermal stability of push-pull 5-substituted-4-oxothiazolidines was studied by DSC, IC and X-ray diffraction techniques.
It was shown that the compounds are stable in the temperature range from room temperature to melting point. The melting is
combined with breaking crystal structure and forming glass material as a new phase that forms crystals by cooling it very
slowly. The rate constant, activation energy as well as activation parameters of process were determined.
Authors:R. K. Verma, L. Verma, M. Chandra, and A. Bhushan
Summary A comparative study of the non-isothermal decomposition of the dl-lactate hydrates of magnesium, calcium and strontium has been made with that of the dl-lactate hydrates chromium(III), manganese(II), iron(II), cobalt(II), nickel(II), copper(II) and zinc(II) keeping dry air as the purge gas and the heating rate maintained at 10 K min-1. While the dl-lactates of manganese(II), cobalt(II) and copper(II) followed single step decomposition scheme suggesting that dehydration and decomposition steps overlapped, the dehydration steps of the other compounds were distinct. &-T plots of none of the dehydration steps showed any induction period, indicating no physical desorption, nucleation or branching. Neither the & max-values nor the onset temperatures of the dehydration steps did show any pattern. The TG data of the dehydration steps have also been analyzed using the Freeman-Carroll, Horowitz-Metzger, Coats-Redfern, Zsakó, Fuoss-Salyer-Wilson and Karkhanavala-Dharwadkar methods. Values of order of reaction, activation energy and Arrhenius factor have been approximated and compared. There are similarities in the activation energy values for the dehydration steps (< 60 kJ mol-1 in general). It is higher with group 2 metals and lower in transition metals (maximum in magnesium and lowest in chromium and iron lactates). In cases of overlapping of dehydration and decomposition steps, the activation energy values are on the lower side with the same trend (lower in cobalt and copper cases).
Resin injection repair is a common method to repair delamination damage in polymer matrix composites (PMCs). To repair high-temperature
PMCs, the resin should have a very low viscosity, yet cure into a compatible adhesive with high temperature stability. Normally,
thermosetting polymers with high glass transition temperatures (Tg) are made from monomers with high room temperature viscosities. Among the high temperature resins, bisphenol E cyanate ester
(BECy, 1,1’-bis(4-cyanatophenyl)ethane), is unique because it has an extremely low viscosity of 0.09–0.12 Pa s at room temperature
yet polymerizes as a cross-linked thermoset with a high Tg of 274°C. BECy monomer is cured via a trimerization reaction, without volatile products, to form the high Tg amorphous network.
In this study, the cure kinetics of BECy is investigated by differential scanning calorimetry (DSC). Both dynamic and isothermal
experiments were carried out to obtain the kinetic parameters. An autocatalytic model was successfully used to model isothermal
curing. The activation energy from the autocatalytic model is 60.3 kJ mol−1 and the total reaction order is about 2.4. The empirical DiBenedetto equation was used to evaluate the relationship between
Tg and conversion. The activation energy of BECy from the dynamic experiments is 66.7 kJ mol−1 based on Kissinger’s method, while isoconversional analysis shows the activation energy changes as the reaction progresses.
Authors:X. Cai, H. Shen, C. Zhang, Y. Wang, and Z. Kong
A simple operation mode to determine the apparent activation energy Ea is introduced. Ea can be determined with a double-curve method by using a constant reaction rate (CRR) approach of Hi-Res TG. The most appropriate
mechanism function f(α) and frequency factor A are determined by a single-curve method when the activation energies provided by the two methods are in good agreement with
each other. The deacetylation of EVA copolymer has been used for illustration. Advantages of the CRR are discussed.
Authors:M. Cieslak-Golonka, E. Ingier-Stocka, and A. Bartecki
The activation energy,Ea taken from the thermal decomposition of KMnO4 and AgMnO4 was compared with the energy of the longest wavelength O→Mn ‘charge transfer’ (CT) transition. TheEa and CT correlation was found in these systems. However, such relationship can be valid when in the dissociation process the
electron transfer is assumed to be the rate determining step. Thus, the permanganates as well as the previously studied chromates,
are positive examples showing that in some cases, the energies derived from both methods can be comparable.
Authors:F. Doğan, M. Ulusoy, Ö. Öztürk, İ. Kaya, and B. Salih
The thermal decomposition kinetics of sterically hindered salen type ligand (L) and its metal complexes [M=Co(II), Ni(II), Cu(II)] were investigated by thermogravimetric analysis. A direct insertion probe-mass spectrometer (DIP-MS)
was used for the characterization of metal complexes of L and all fragmentations and stable ions were characterized. The thermogravimetry and differential thermogravimetry (TG-DTG)
plots of salen type salicylaldimine ligand and complexes showed a single step.
The kinetic analysis of thermogravimetric data was performed by using the invariant kinetic parameter method (IKP). The values
of the invariant activation energy, Einv and the invariant pre-exponential factor, Ainv, were calculated by using Coats-Redfern (CR) method. The thermal stabilities and activation energies of metal complexes of
sterically hindered salen type ligand (L) were found as Co(II)>Cu(II)>Ni(II)>L and ECu>ENi>ECo>L. Also, the probabilities of decomposition functions were investigated. The diffusion functions (Dn) are most probable for the thermal decomposition of all complexes.
Authors:O. N. Nikulicheva, V. P. Fadeeva, and V. A. Logvinenko
The paper reports the calculation of kinetic parameters (activation energy, pre-exponent and reaction order) of thermodegradation of some phenol stabilizers. For this purpose, a software package for IBM-compatible personal computers is proposed. The first calculation of kinetic parameters (E, Z, n) was carried out for these compounds. The package can be applied for kinetic calculations on the thermodegradation of other substances.
In this work the influence of Cu admixtures on the crystallization process of amorphous Fe-Si-B alloys is studied, based on
measurements of differential thermal calorimetry of the series Fe75-xCuxSi9B16 (x=0, 1, 2, 2.8 and 3.5) during their heating with different heating rates. The first crystallization stage can not be traced
for any of the amounts of Cu content examined, while the second stage is observed only when the Cu content is 1 at%. The activation
energy as estimated with Kissinger's method for the third crystallization stage has a mean value of 326 kJ mol-1 and with the isoconversional Flynn, Wall and Ozawa method is almost constant when 0.05<a<0.6 and exhibits a small monotical
decrease when a>0.6. The main crystallization peak can not be described by means of a single JMA-type function.
Authors:M. Núñez, M. Villanueva, B. Rial, and L. Núñez-Regueira
The thermal degradation of the epoxy systems diglycidyl ether of bisphenol A (BADGE n=0)/1, 2 diamine cyclohexane (DCH) and diglycidyl ether of bisphenol A (BADGE n=0)/1, 2 diaminecyclohexane (DCH) containing calcium carbonate filler immersed and not immersed in hydrochloric acid have
been studied by thermogravimetric analysis in order to compare their decomposition processes and to determine the reaction
mechanism of the degradation processes. The value of the activation energies, necessary for this study, were calculated using
various integral and differential methods. Analysis of the results suggests that hydrochloric acid does not affect the decomposition
of the epoxy network and that the reaction mechanisms produce sigmoidal-type curves for the systems not immersed in HCl and
deceleration curves for the same systems immersed.
Authors:B. Janković, B. Adnađević, and J. Jovanović
An isothermal dehydration of equilibrium swollen poly(acrylic acid) hydrogel in the temperature range from 306 to 361 K was
investigated. The specific parameters connected with shape of the conversion curves were defined. The activation parameters
(E, lnA) of the isothermal dehydration of equilibrium swollen poly(acrylic acid) hydrogel were calculated, using Johnson-Mehl-Avrami
(JMA), ‘initial rate’ and ’stationary point’ methods. The reaction models for the investigated dehydration are determined
using the ‘model-fitting’ method. It was established that both, the reaction model and activation parameters of the hydrogel
dehydration were completely different for the isothermal process than for the non-isothermal one. It was found that the increase
in dehydration temperature lead to the changes in isothermal kinetic model for the investigated hydrogel dehydration. It was
established that the apparent activation energy (E) of hydrogel dehydration is similar to the value of the molar enthalpy
of water evaporation.