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Abstract  

A direct and simple method for the conversion of UO2 and U3O8 powder into uranyl sulphate solution is described, eliminating many tedious chemical steps. UO2 and U3O8 are not soluble in concentrated or dilute sulphuric acid, as uranium in lower oxidation state does not react with sulphuric acid. However, nitric acid oxidizes uranium from lower valency to higher valency state, i.e., tetravalent to the hexavalent uranyl ion in solution. Sufficient amount of sulphuric acid present in the reaction mixture makes it possible for uranyl ions, formed by oxidation of nitric acid, to react with sulphuric acid forming uranyl sulphate.

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Abstract  

Sn-plating of aluminum alloy before and after a post-molybdate treatment is characterized by 119Sn conversion electron Mössbauer spectrometry (CEMS). CEMS results gave the direct evidence that the oxidation resistance of Sn-coated aluminum alloy is improved by the post-molybdate treatment. Depth selective CEMS showed that the coating structures consist of SnO2 on the top coating and the mixed Sn(0) and Sn(II) species in the intermediate layers. The Sn(II) oxide exists abundantly near the interface between the aluminum alloy and the Sn coating rather than beneath SnO2 layer.

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The Korea Atomic Energy Research Institute (KAERI) has launched a decommissioning program of the uranium conversion plant. The sludge waste, which was generated during the operation of the plant and stored in the lagoon, was characterized for the development of the treatment process. The physical properties were measured and chemical compositions and radiological properties analyzed. The main compounds of the sludge were ammonium nitrate, sodium nitrate, calcium nitrate, and calcium carbonate. All heavy radioactive elements such as uranium, thorium and 226Ra were precipitated and deposited at the bottom, and were not dissolved in the concentrated nitrate solution. A possible flow-scheme for processing is presented.

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57Fe Conversion electron Mössbauer spectroscopy, X-ray diffractometry and electron microprobe measurements were performed on Fe–Ni–Cr alloys coatings electrochemically deposited at different times (from 1 to 29 minutes). Significant differences have been found among the Mössbauer spectra of samples examined. The changes are also reflected by the hyperfine field distribution derived from the spectra. The observed changes can be associated with changes in the magnetic anisotropy and in the short range ordering in correlated to the duration of electrochemical deposition.

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This study is devoted to the thin-layer chromatographic demonstration of spontaneous chiral conversion of l-hydroxyproline (l-Hyp) to d-hydroxyproline (d-Hyp), and to its spontaneous peptidization, when dissolved in 70% aqueous methanol and stored at room temperature in a stoppered glass vessel. The adopted enantioseparation conditions were the same ones, as employed earlier for a successful enantioseparation of l- and d-proline. To this effect, we used microcrystalline cellulose as stationary phase and a quaternary mixture composed of 2-butanol:pyridine:glacial acetic acid:water (30:20:4:24, v/v) as mobile phase. Structural difference between proline and hydroxyproline consists in the presence of one hydroxyl group per molecule of the latter amino acid, which makes the respective enantioseparation a more difficult task. Consequently, the obtained separation effect was not a complete (i.e., a baseline) resolution of the two Hyp antimers yet a sufficient enough proof of the appearance of d-Hyp, apparently due to spontaneous chiral conversion taking place in the course of the l-Hyp solution storage and ageing period. The condensation products were discovered both in the fresh and the aged l-Hyp solution, yet in the aged sample, the condensation product yields were considerably higher than in the freshly prepared one (as convincingly demonstrated by mass spectrometry). Demonstration of the condensation products was performed with the aid of thin-layer chromatography (TLC), liquid chromatography-mass spectrometry (LC-MS), and thin-layer chromatography-mass spectrometry (TLC-MS).

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The comprehensive analysis of volatile β-diketonate compound—ruthenium(III) trifruoroacetylacetonate (Ru(tfac)3)—was carried out. By means of flow method in quasi-equilibrium conditions and static method the temperature dependencies of saturated vapor pressure have been measured over solid and liquid cis- and trans-modifications of Ru(tfac)3 and isomer mixture. The thermodynamic characteristics of sublimation, evaporation, melting, and phase conversion have been calculated for structural isomers. Also by differential-scanning calorimetry the temperature meanings and the thermodynamic characteristics of melting have been determined for individual isomers of Ru(tfac)3 and their mixtures. By XRD the structures for cis- and trans-modifications have been determined. Both structures consist of neutral molecules arranged in pseudo layers.

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Abstract  

Correlated measurement of the lifetime and of the lineshape of the 511 keV annihilation radiation of positrons (age-momentum correlation, AMOC) has become a powerful tool for investigating reactions of positron or positronium in condensed matter as a function of time. The beam-based + AMOC method installed at the Stuttgart relativistic positron beam facility (E kin e+ 4MeV) offers substantial advantages over the conventional E coincidence technique resulting in a fast data taking due to the unity detection efficiency of the + scintillator which provides the start signal for the lifetime measurement. In this paper the application of AMOC to positronium chemistry is illustrated by the study of spin conversion of positronium in the system methanol/HTEMPO as a function of HTEMPO (4-hydroxy-2,2,6,6-tetramethylpiperidine-1-oxyl, a paramagnetic solute) concentration. The same technique can be applied to other systems and other reactions in positronium chemistry, e. g., oxidation or complex formation.

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Manganese oxide samples obtained from thermal decomposition of manganese carbonate at 400 and 600 °C were subjected to different doses of g-irradiation within the range 0.2 to 1.6 MGy. The surface and catalytic properties of the above samples were studied using nitrogen adsorption isotherms measured at -196 °C and catalytic conversion of ethanol and isopropanol at 300-400 °C using micropulse technique. The results obtained revealed that manganese oxides obtained at 400 °C consisted of a mixture of Mn2O3 and MnO2 while the samples calcined at 600 °C composed entirely of Mn2O3. Gamma-irradiation resulted in a decrease in the particle size of manganese oxide phases with subsequent increase in their specific surface areas. Gamma-irradiation with 0.2 and 0.8 MGy effected a measurable progressive decrease in the catalytic activity in dehydration and dehydrogenation of both alcohols. However, the treated catalyst retained their initial activity upon exposure to a dose of 1.6 MGy. Also, g-irradiation increased the selectivities of the investigated solids towards dehydrogenation of both alcohols. The catalyst samples precalcined at 600 °C exhibited higher catalytic activities than those precalcined at 400 °C.

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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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). Even though the world has large deposits of natural gas, most of this is located in remote areas and, consequently, it must be transported to its markets. Conversion of methane to more useful and easily transportable chemicals (liquids) has therefore

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