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Abstract  

Emanation thermal analysis (ETA) was used to characterize the thermal reactivity of amorphous brannerite mineral of general formula U1–xTi2+xO6 (locality El Cabril, near Cordoba, Spain). It was demonstrated that on sample heating up to 880C microstructure changes taking place in the sample were accompanied by the formation of new radon diffusion paths, followed by their closing up during the final transformation of amorphous to crystalline brannerite in the range 900–1020 C. Relative changes in structure irregularities that served as radon diffusion paths during heating and subsequent cooling of the sample to temperatures of 300, 550, 750, 880, 1020 and 1130C, respectively, were determined from the ETA results. Mass losses in temperature ranges of 230–315, 570–760 and 840–1040C were observed by thermogravimetry. Mass spectrometry indicated the release of CO2 mainly due to the decomposition of minor carbon amount in the brannerite mineral sample.

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Abstract  

The hydrogen-isotope exchange reaction between HTO vapor (as a gaseous material) andp-aminophenol (or -alanine) (as a solid material) having two different kinds of functional groups, has been studied to reveal the reactivity of the compounds. The reaction has been analyzed by the A-McKay plot method and the rate constants (k) for each group have been obtained. Comparison ofk leads to the following: (1) the effect of the NH2 group inp-aminophenol on the reactivity is greater than that in -alanine, and (2) the reactivity of compounds having two different kinds of functional groups can be analyzed by the A-McKay plot method only.

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Reaction Kinetics, Mechanisms and Catalysis
Authors: Raquel Cristóvão, Priscilla Amaral, Ana Tavares, Maria Coelho, Magali Cammarota, José Loureiro, Rui Boaventura, Eugénia Macedo, and Fernando Pessoa

Abstract  

In this work, the laccase catalyzed degradation of reactive textile dyes was studied in supercritical carbon dioxide media. A two level Box–Behnken factorial design with two factors and response surface methodology (RSM) were performed to investigate and optimize the effects of pressure and temperature on reactive red 239 (RR239), reactive yellow 15 (RY15) and reactive black 5 (RB5) dye degradations by commercial laccase in supercritical carbon dioxide media. Mathematical models were developed for each dye showing the effect of each factor and their interactions on color removal. Pressure and the interaction between temperature and pressure were the main factors affecting the decolorization. The optimum conditions for RB5 and RY15 were found to be high pressure values (>120 bar), whilst the temperature presented a minor effect on their degradation at these pressures. For RR239, both variables influenced the decolorization and the optimum conditions appear to be at low values of pressure and high values of temperature.

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DTA and XRD measurements were carried out with reactive precursors taken from the YO1.5-BaO-CuO system in order to investigate mechanisms of YBa2Cu3O7−x formation. The reactions taking place depend strongly on phase composition, phase purity, powder size and heating rate. Among the examined reactive precursors a mixture of 7Y2O3+22BaCuO2+10CuO turned out as the most suited for melt-processing.

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Abstract  

In order to reveal the behavior of the hydrogen atoms in an ammonium salt, the hydrogen-isotope exchange reaction between each of the three ammonium halides and tritiated water vapor was followed at 50–80°C. Analyzing the data obtained by theA -McKay plot method, the following has been quantitatively clarified: both the reactivity of an ammonium halide and the temperature dependence of its reactivity increase when the electronegativity of the halogen element in the ammonium halide is larger.

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The role of structural parameters strongly influencing the course of heterogeneous solid-state reactions is established. Owing to the close relationship between the form and reactivity of solids, due emphasis must be given to detailed morphological studies. This allows the derivation of consistent correlations between the reaction mechanism on a microscopic scale and the observed macroscopic changes.

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Abstract  

The radiolysis of tetracycline hydrochloride dissolved in benzyl alcohol has been studied at 77 K by ESR. The H. and e which are formed in the radiolysis of benzyl alcohol at 77 K migrate over a distance corresponding to about 95 and 995 molecules of solvent, respectively, before they are captured by the tetracycline hydrochloride solute. This distance corresponding to H. is smaller than the distance that it migrates in a neopentane matrix. The migration of H. in neopentane matrix is more favoured than in benzyl alcohol matrix. When the mole ratio between solute and solvent is 110000, the reactivity of H. observed by ESR is the following: a) 20% of H. reacts preferentially with solute because EH(sin )2 < (Emp)solvent; b) 80% of H. reacts exclusively with the solvent in the firsst collision because EH(sin )2 > (Emp)solvent. The crystal structure of benzyl alcohol presents inherent factors which do not favour the migration of H. at 77 K.

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Abstract

Vent sizing package 2 (VSP2) was used to measure the thermal hazard and runaway characteristics of 18650 lithium-ion batteries, which were manufactured by Sanyo Electric Co., Ltd. Runaway reaction behaviors of these batteries were obtained: 50% state of charge (SOC), and 100% SOC. The tests evaluated the thermal hazard characteristics, such as initial exothermic temperature (T 0), self-heating rate (dT dt −1), pressure-rise rate (dP dt −1), pressure temperature profiles, maximum temperature, and pressure which were observed by adiabatic calorimetric methodology via VSP2 using customized test cells. The safety assessment of lithium-ion cells proved to be an important subject. The maximum self-heating rate (dT dt −1)max and the largest pressure-rise rate (dP dt −1)max of Sanyo 18650 lithium-ion battery of 100% SOC were measured to be 37,468.8 °C min−1 and 10,845.6 psi min−1, respectively, and the maximum temperature was 733.1 °C. Therefore, a runaway reaction is extremely serious when a lithium-ion battery is exothermic at 100% SOC. This result also demonstrated that the thermal VSP2 is an alternative method of thermal hazard assessment for battery safety research. Finally, self-reactive ratings on thermal hazards of 18650 lithium-ion batteries were studied and elucidated to a deeper extent.

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Abstract  

The modified 135Xe equilibrium reactivity in the Syrian Miniature Neutron Source Reactor (MNSR) was calculated first by using the WIMSD4 and CITATION codes to estimate the four-factor product (ε p P fnl P tnl). Then, precise calculations of 135Xe and 149Sm concentrations and reactivities were carried out and compared during the reactor operation time and after shutdown. It was found that the 135Xe and 149Sm reactivities did not reach their equilibrium reactivities during the daily operating time of the reactor. The 149Sm reactivities could be neglected compared to 135Xe reactivities during the reactor operating time and after shutdown.

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The glass transition temperature,T g is a sensitive and practical parameter for following cure of reactive thermosetting systems. A new equation was developed for predicting theT g-conversion relationship based on the Dillman-Seferis viscoelastic compliance model. It assumes that the changes inT g are primarily due to changes in relaxation time as chain extension and crosslinking reduce the mobility of a polymer network. Such information is essential in combining kinetic and viscoelastic measurements, which monitor transformations of thermosets during cure. The equation derived from the viscoelastic model was shown to be applicable for a variety of experimental data. The success of the methodology was further demonstrated by comparing well-established relations, such as the Fox equation and the Di-Benedetto equation, to predictions made possible by adjusting two viscoelastic model parameters. Finally, the fitting power of the proposed equation was shown by fitting published epoxy data from the literature as well as experimental data on a relatively new resin system such as dicyanates used as a model in this study.

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