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Abstract  

Thermal degradation kinetics of copolymers based on bis-phenol A ethoxylated dimethacrylate (Bis-EMA) with triethylene glycol dimethacrylate (TEGDMA), and urethane dimethacrylate (UDMA) with TEGDMA in wt/wt ratios 30/70, 50/50, or 70/30 were investigated using thermogravimetric analysis as a means to provide specific information regarding the internal structures of these resins. Thermogravimetric scans were taken at four different heating rates to perform an isoconversional analysis to determine the change of the effective activation energy as a function of conversion. A two-step degradation mechanism was found to occur in almost all copolymer compositions attributed to the existence of inhomogeneities in the macromolecular structure and the formation of weak links inside the polymeric network.

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The kinetics of individual stages of thermal decomposition of Al2(SO4)3·18H2O were studied by TG method. It is found that Al2(SO4)3·18H2O decomposes to Al2O3 in four major stages, all of endothermic. Some of these major stages are formed by sub-stages. The first three major stages are dehydration reactions in which two, ten and six moles water are lost, respectively. The last major stage is sulfate decomposition. In this study the kinetic parameter values of these major and sub-stages were calculated by integral and differential methods. The alterations of activation energies with respect to the decomposition ratio and to the method were investigated.

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Transparent glasses of SrBi2B2O7 (SBBO) were fabricated via the conventional melt-quenching technique. The amorphous and the glassy nature of the as-quenched samples were, respectively, confirmed by X-ray powder diffraction (XRD) and differential scanning calorimetry (DSC). The glass transition (T g) and the crystallization parameters [crystallization activation energy (E cr) and Avrami exponent (n)] were evaluated under non-isothermal conditions using DSC. There was a close agreement between the activation energies for the crystallization process determined by Augis and Bennet and Kissinger methods. The variation of local activation energy [E c(x)] that was determined by Ozawa method, decreased with the fraction of crystallization (x). The Avrami exponent (n(x)) increased with the increase in fraction of crystallization (x) suggesting that there was a change over in the crystallization process from the surface to the bulk.

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Dielectric Thermal Analysis (DETA) of drugs, proteins and amino acids reveals a strongly linear conductivity increase prior to and peaking at the melt, associated with dielectric viscoelastic properties of the material. Premelt onset and peak are shown to depend on thermal history. Comparisons of neat amino acid samples to samples heated to 150 °C; dried in a desiccator; or heated above their melting point and cooled show significant premelt and melt shifts. Melts are also correlated with phase transitions observed by Differential Scanning Calorimetry (DSC). Activation energies attributed to charging in the premelt for amino acids were typically 250 J/mole.

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Abstract  

A series of coordination polymers, cobalt(II)–[dipicolylamide-propyl poly(dimethylsiloxane)]s (Co-DPPDMS), was prepared and studied by thermogravimetry (TG) and double-shot pyrolysis-gas chromatograph-mass spectrometry (Pyro-GC-MS). The TG curves of the Co-DPPDMSs exhibited two events for the mass loss, and the Pyro-GC-MS results suggested that the decomposition reaction of the PDMS chains in the ligand polymer occurred at the second event. The activation energy E a and the reaction order n of each event were estimated by curve fitting based on the order rate equation, and the results were compared with those obtained using the Kissinger method for non-isothermal degradation.

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(N-diethylaminoethyl)-4-iodobenzamide (IBZA) has been labeled with radioactive iodine via nucleophilic substitution radioiodination using copper chloride as a catalyst. The factors affecting the radiochemical yield of the labeling of IBZA such as pH of the medium, substrate concentration, reaction time, cuprous chloride concentration and temperature were investigated. Chromatographic analysis technique has been used to determine the radiochemical yield and purity. Kinetics and thermodynamic parameters indicated a second order reaction. Activation energies for the isotopic exchange reaction between IBZA and 125I were calculated to be 5.352 and 4.767 kcal/mol (22.39 and 19.94 kJ/mol) without and with catalyst respectively.

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The objective of this research was to investigate the effect of different clay composition and concentrations on the thermal behaviour and kinetics of heavy crude oil in limestone matrix by thermogravimetry (TG/DTG). In TG/DTG experiments, three distinct reaction regions were identified in all of the crude oil + limestone mixture known as low temperature oxidation (LTO), fuel deposition (FD) and high temperature oxidation (HTO) respectively. Addition of clay to porous matrix significantly affected the reaction regions. Significant reduction of activation energy due to addition of clay to crude oil indicates the catalytic effect of clay on crude oil combustion.

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The purpose of this work is to evaluate the thermal and kinetic behavior of biodiesel derived from soybean and higuereta oils. The thermogravimetric profiles of biodiesels indicated one step associated with decomposition of the ethyl esters. The thermal profiles were compared with reference diesel. Kinetic parameters were obtained by thermal analysis, estimating reaction order, pre-exponential factor and activation energy. For estimation of the kinetic parameters the Coats & Redfern method was used. The selection criterion of best fit was based on the correlation coefficient of the linear regression and the compensation effect of the kinetic parameters.

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