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Journal of Thermal Analysis and Calorimetry
Authors: M. Daviti, K. Chrissafis, K. Paraskevopoulos, E. Polychroniadis, and T. Spassov

Abstract  

The kinetics of the α-β phase transition of HgI2 were investigated by isothermal and non-isothermal differential scanning calorimetry. The effective activation energy of the transition, 41540 kJ mol-1, was determined applying the methods of Kissinger and Ozawa. The transition kinetics were described by the Johnson-Mehl-Avrami model and the value of the Avrami exponent n was found to range from high values (n>3) at the early stages to lower values at later stages of the transformation, with an average value of 2.

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The dehydration of LiCl·H2O was studied under inert helium atmosphere by DTA/TG for different heating rates. The dehydration of LiCl·H2O proceeds through a two step reaction between 99–110 and 160–186°C, respectively. It leads to the formation of LiCl·0.5H2O as intermediate compound. The proposed mechanism is: article image and article image Based on the temperature peak of the DTA signals the activation energies of the two reactions were determined to be 240 kJ mol−1 (step 1) and 137 kJ mol−1 (step 2), respectively.

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Abstract  

The thermal degradation of ethylene-vinyl acetate (EVA), ethylene-vinyl-3,5-dinitrobenzoate (EVDNB) and ethylene-vinyl alcohol (EVAL) copolymers have been studied using differential thermal analysis (DTA) and thermogravimetry (TG) under isothermal and dynamic conditions in nitrogen. Thermal analysis indicates that EVA copolymers are thermally more stable than EVDNB samples. The degradation of the copolymers considered occurs as an additive degradation of each component polyethylene (PE) and poly(vinyl acetate) (PVA), poly(vinyl-3,5-dinitrobenzoate) (PVDNB) or poly(vinyl alcohol) (PVAL). The apparent activation energy of the decomposition was determined by the Kissinger and Flynn-Wall methods which agree well.

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Journal of Thermal Analysis and Calorimetry
Authors: M. Matthews, I. Atkinson, Lubaina Presswala, O. Najjar, Nadine Gerhardstein, R. Wei, Elizabeth Rye, and A. Riga

Abstract  

Dielectric analysis (DEA), supported by thermogravimetric analysis (TG), differential scanning calorimetry (DSC), powder X-ray diffraction analysis (PXRD) and photomicrography, reveal the chiral difference in the amino acids. The acids are classified as dielectric materials based on their structure, relating chirality to the vector sum of the average dipole moment, composed of the constant optical (electronic) and infra-red (atomic) polarizabilities, as well as dipole orientation. This study encompasses 14 L-and D-amino acid isomers. Physical properties recorded include AC electrical conductivity, charge transfer complexes, melting, recrystallization, amorphous and crystalline phases, and relaxation spectra, activation energies and polarization times for the electrical charging process.

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Journal of Thermal Analysis and Calorimetry
Authors: W. Sułkowski, S. Mistarz, T. Borecki, M. Moczyński, A. Danch, J. Borek, M. Maciążek, and Anna Sułkowska

Abstract  

From the TG data of rubber granulates, different polyurethane and composites it can be seen that the thermal decomposition for the rubber granulate and all of the composites start above 520 K. Two major mass losses for the rubber granulates and majority of the composites were observed and thermal decomposition is essentially complete by ~820 K. The changes of activation energies of lower and higher temperature decomposition, calculated according to the different equations were observed for a priori assumed first-order reaction for devolatilisation. Differences between determined and calculated results could suggest a possible reaction between polyurethane agents and rubber granulate during the composites formations.

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Journal of Thermal Analysis and Calorimetry
Authors: G. Vázquez, J. González-Álvarez, and G. Antorrena

Abstract  

The curing of a phenol–formaldehyde–tannin (PFT) adhesive in the presence of pine or eucalyptus wood has been studied using differential scanning calorimetry. The influence of the adhesive/wood ratio on the activation energy (E a), the temperature of the maximum of the exothermic peak (T p) and the enthalpy of the curing process (ΔH) was analysed. E a, T p and ΔH of the curing reaction decreased when wood was added in the curing system. The adhesive/wood interaction did not depend significantly on wood species.

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In this research, pyrolysis and combustion behavior of three different oil shale samples from Turkey were characterized using thermal analysis techniques (TG/DTG). In pyrolysis experiments, two different mechanisms causing mass loss were observed as distillation and cracking. In combustion experiments, two distinct exothermic peaks were identified known low and high temperature oxidation. On the other hand, determination of activation energies are required for the estimation of oil extraction conditions from the oil shales. Differential methods are used to determine the activation energies of the samples where various f(α) models are applied from the literature. It was observed that the activation energies of the all oil shale samples are varied between 13.1–215.4 kJ mol−1 in pyrolysis and 13.1–408.4 kJ mol−1 in combustion experiments which are consistent with other kinetic results.

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Abstract  

Ammonium dinitramide (ADN) prills were prepared by emulsion crystallization and characterized by optical microscopic, thermogravimetric (TG) and differential scanning calorimetric (DSC) techniques. The isothermal and non-isothermal decomposition kinetics of ADN prills were studied by TG. The differential isoconversional method of Friedman (FR) and integral isoconversional method of Vyazovkin were used to investigate the dependence of activation energy (E a) with conversion (α) and the results were compared with literature data. The dependence of activation energy was also derived from isothermal data. A strong dependence of E a with α is observed for the ADN prills. All the methods showed an initial increase in E a up to α=∼0.2 and later decreases over the rest of conversion. The apparent E a values of FR method are higher than that of Vyazovkin method up to α=∼0.45. The calculated mean E a values by FR, Vyazovkin and standard isoconversional method for α between 0.05 and 0.95 were 211.0, 203.9 and 156.9 kJ mol−1, respectively.

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Abstract  

Results of phase transformations, enthalpy released and specific heat of Ge22Se78–xBix(x=0, 4 and 8) chalcogenide glasses, using differential scanning calorimetry (DSC), under non-isothermal condition have been reported and discussed. The glass transition temperature, T g, is found to increase with an average coordination number and heating rates. Following Gibbs—Dimarzio equation, the calculated values of T g (i.e. 462.7, 469.7 and 484.4 K) and the experimental values (i.e. 463.1, 467.3 and 484.5 K) increase with Bi concentration. Both values of T g, at a heating rate of 5 K min–1, are found to be in good agreement. The glass transition activation energy increases i.e. 102±2, 109±3 and 115±8 kJ mol–1 with Bi concentration. The demand for thermal stability has been ensured through the temperature difference T cT g and the enthalpy released during the crystallization process. Below T g, specific heat has been observed to be temperature independent but highly compositional dependent. The growth kinetic has been investigated using the Kissinger, Ozawa, Matusita and modified JMA equations. Results indicate that the crystallization ability is enhanced, the activation energy of crystallization increases with increasing the Bi content and the crystal growth of these glasses occur in 3 dimensions.

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Abstract  

Sodium, ferric and aluminum salts of oxycellulose and the amphoteric ion exchanger derivatives from cationized oxycellulose were prepared. Thermal behaviour of the different samples was investigated by thermal gravimetric analysis (TG) and derivative thermogravimetric (DTG) technique. The rate constant and the activation energy were estimated. Infrared spectroscopy of the different samples were investigated, analyzed and discussed.

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