Authors:M. Matthews, I. Atkinson, Lubaina Presswala, O. Najjar, Nadine Gerhardstein, R. Wei, Elizabeth Rye, and A. Riga
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.
Authors:W. Sułkowski, S. Mistarz, T. Borecki, M. Moczyński, A. Danch, J. Borek, M. Maciążek, and Anna Sułkowska
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.
Authors:M. Dolores Fernández and M. Jesús Fernández
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.
Authors:G. Vázquez, J. González-Álvarez, and G. Antorrena
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 (Ea), the temperature of the
maximum of the exothermic peak (Tp)
and the enthalpy of the curing process (ΔH)
was analysed. Ea, Tp 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.
Authors:M. Gönen, D. Balköse, F. İnal, and S. Ülkü
In this research, the effects of zinc stearate addition on paraffin wax degradation were investigated by differential scanning
calorimetry (DSC) and thermogravimetry (TG). The apparent activation energies of wax decomposition in nitrogen and air atmospheres
were determined as 76 and 37 kJ mol−1, respectively applying Kissinger method to TG data. The degradation rate constants of paraffin containing zinc stearate (0.1–0.5%)
were found to be almost two times greater than that of paraffin only in air atmosphere. However, zinc stearate did not affect
the rate constants in nitrogen significantly.
Reaction kinetics of the formation of TiC by calciothermic reduction of TiO2 in presence of carbon have been investigated using thermal analysis (TG-DTA) of a powder mixture of TiO2, Ca, and C in argon atmosphere at different heating rates. Both the reaction initiation and the peak temperatures are found
to increase with heating rates. The appearance of exothermic peaks in the DTA plots after Ca melting indicates the reduction
of TiO2 by liquid calcium and formation of TiC by in-situ reaction of Ti with C. The apparent activation energy of the process has
been found to be 170.80.5 kJ mol-1.
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:
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.
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 (Ea) 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 Ea with α is observed for the ADN prills. All the methods showed an initial increase in Ea up to α=∼0.2 and later decreases over the rest of conversion. The apparent Ea values of FR method are higher than that of Vyazovkin method up to α=∼0.45. The calculated mean Ea 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.
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, Tg, is found to increase with an average coordination number and heating rates. Following Gibbs—Dimarzio equation, the calculated values of Tg (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 Tg, 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 Tc–Tg and the enthalpy released during the crystallization process. Below Tg, 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.