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  • gamma irradiation  (1)
  • mechanochemistry  (1)
  • 1
    ISSN: 1572-879X
    Keywords: MoS2 ; WS2 ; thiosalts ; in situ activation ; hydrodesulfurization ; mechanochemistry
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology
    Notes: Abstract The in situ decomposition of ammonium thiometallates during the hydrodesulfurization (HDS) of dibenzothiophene (DBT), to obtain molybdenum disulfide and tungsten disulfide catalysts, was investigated. It was found that very efficient catalysts for the HDS of DBT were obtained by in situ decomposition. Mechanical uniaxial pressing of the precursors (ammonium thiometallates) affected both textural and catalytic properties of the catalysts. Surface areas of molybdenum and tungsten disulfides increased as a function of uniaxial pressing, while catalytic activities went through a maximum. For MoS2, the hydrogenation selectivity was much higher for in situ catalysts than for ex situ ones. For WS2 catalysts, the hydrogenation selectivity was less sensitive to the condition of decomposition (ex situ/in situ). The surface S/M (M = Mo, W) atomic ratio from the Auger signal decreased as a function of uniaxial pressing, while the C/M ratio remained almost constant at 1.6. The best catalyst showed an experimental S/Mo ratio that is slightly higher than the stoichiometric value. The effect of in situ decomposition and mechanical deformation of thiometallate precursors is discussed.
    Type of Medium: Electronic Resource
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  • 2
    ISSN: 1572-9605
    Keywords: YBaCuO ; gamma irradiation ; critical current density ; flux pinning
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We investigated the flux pinning behavior induced by gamma irradiation in Y1Ba2Cu3O(7−x) silver-added samples. The superconductors were prepared through solid-state route and added with silver in amounts of 0-, 6.5-, and 20-wt%, following which the samples were irradiated by high-energy gamma irradiation (γ) at doses of 0, 500, and 1500 kGy at the dosage rate of 8.2 kGy/h. We performed magnetization loops to study the flux pinning of vortex in YBCO/Ag superconductors. We found that silver addition and irradiation on superconductors may increase the width in magnetization loops, which is related to the enhancement in the critical current density, J c . We established that an interaction between silver addition and irradiation that results in higher values in J c for YBCO/Ag irradiated samples already exists. The J c in samples containing 20-wt% of silver decreased with irradiation because a higher content of silver produces small crystals and secondary phases growing. On comparing the TGA analysis for both YBCO and YBCO/Ag samples, we found higher-weight oxygen losses in YBCO silver samples, which suggests that silver increases the oxygen saturation content. The higher oxygen content found on irradiated specimens it is indicative of oxygen losses from CuO chains or CuO2 planes reached by γ-irradiation.
    Type of Medium: Electronic Resource
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