Showing papers by "Gholam-Abbas Nazri published in 2006"

Short communication Catalytic activity of oxides and halides on hydrogen storage of MgH2

Abstract: Hydrogen sorption kinetics of ball milled MgH2 with and without chemical additives were studied. We observed kinetics and capacity improvement with increasing the number of sorption cycles that contributed to the micro/nano cracking of MgH2 particles, shown by XRD and SEM studies. In addition, to investigate the proposed specific role of O 2− -based additives on the sorption kinetics of MgH2, we have undertaken a comparative study evaluating the performances of MgH2 containing the NbCl5, CaF2 or Nb2O5 additives. At 300 ◦ C, addition of NbCl5 and CaF2 improved the sorption capacity to 5.2 and 5.6 wt% within 50 min, respectively, in comparison to the required 80 min in the case of Nb2O5. This suggests the importance of the chemical nature of the catalyst for hydrogen sorption in MgH2. In addition, the catalyst specific surface area was shown to be very critical. High surface area Nb2O5 (200 m 2 g −1 ), prepared by novel precipitation method, exhibits an excellent catalytic activity and helped to desorb 4.5 wt% of hydrogen from MgH2 within 80 min at a temperature as low as 200 ◦ C.

Structure—Property Correlations in Solid Solutions of (CuI)8P12‐xAsx, 2.4 ≤ x ≤ 6.6.

Abstract: A series of P/As mixed pnicogen phases of composition (CuI)8P12−xAsx, in which x=2.4, 4.2, 4.8, 5.4, and 6.6, have been synthesized and characterized by X-ray single crystal and powder diffraction, solid-state NMR spectroscopy, thermal gravimetric analysis, and impedance spectroscopy. These materials are isostructural to (CuI)8P12 and consist of neutral, tubular P/As mixed pnicogen chains associated with CuI and I− ions. The As is distributed throughout the pnicogen chains; however, the “roof” sites of the [P8] cage show preferred occupation by As relative to the other sites. Accordingly, the change in cell volume is not a linear function of the As incorporation. Solid-state 31P NMR spectroscopy of the 40 % As incorporated sample are consistent with the X-ray structural model, with extensive broadening due to 31P–75As coupling and site disorder, and a change in the chemical shifts of the resonances due to the As substitution into the lattice. The degree of copper ion site disorder, probed by single-crystal X-ray diffraction, increases with increasing As content. Although very little change is observed in the copper ionic conductivity of polycrystalline samples, which ranges from 1.8–5.1×10−6 S cm−1 for (CuI)8P12−xAsx, x=0, 4.2, 5.4; a single crystal (x=4.8) measured along the needle axis has a conductivity of 1.7×10−3 S cm−1 at 128 °C. This represents an order of magnitude improvement in conductivity over (CuI)8P12 at the same temperature.