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Milanese C.,University of Pavia | Girella A.,University of Pavia | Garroni S.,Autonomous University of Barcelona | Bruni G.,University of Pavia | And 3 more authors.
International Journal of Hydrogen Energy | Year: 2010

Ternary Mg-Nb2O5 - graphitic C mixtures (molar ratio % = 97.5:0.5:2.0) were prepared by high-energy ball milling (BM) under Ar for different times (from 0.25 h to 4 h) and thoroughly characterized by manometric, calorimetric, X-ray powder diffraction, and scanning electron microscopy analyses. The aims of the work were: - to assess the effect of the simultaneous presence of the two dopants on the reactivity and the sorption properties of the Mg-MgH2 system; - to study the influence of the milling time on the performance of the mixtures. Neither milling nor the high temperature/high pressure treatments led to reactions among the components of the mixtures, and Mg was the only hydrogen active phase. After 4 activation cycles at 623 K and 35 bar/1 bar charging/discharging pressure, the mixture milled for 1 h was the best performing one: it reversibly charged up to 6.8 wt% H2 with absorption/desorption rates 64/4.5 times higher than those of a pure Mg sample BM for the same time and activation energies 3.6/2 times lower. The desorption temperature and the dehydrogenation enthalpy of the ternary mixture were respectively 40 K and 4 kJ/mol H2 lower than those of pure MgH 2. © 2009 Professor T. Nejat Veziroglu. Published by Elsevier Ltd. All rights reserved.

Basak A.K.,Catholic University of Leuven | Zein Eddine W.,Catholic University of Leuven | Celis J.-P.,Catholic University of Leuven | Matteazzi P.,CSGI and MBN Nanomaterialia Spa
Journal of Nanoscience and Nanotechnology | Year: 2010

The feasibility of achieving a nanostructured material after different thermal processing of nanosized powders is presented. The thermal processing was done by either atmospheric plasma spraying, laser sintering, or extrusion followed by hot isostatic pressing. The structural characterisation of such thermally processed nanostructured Fe-based and Cu-based metallic or Al 2O 3 reinforced cermets, confirmed the retention of a nanostructure after each of these thermal processes. Hardness measurements confirmed an increased hardness as expected in the case that nanostructuring is achieved. The role of grain boundaries and second phase particles on the retention of the nanostructure after thermal processing is discussed. Finally, the possible benefit of nanostructuring on the friction and wear behaviour of materials in sliding tests against corundum in ambient air is reported and discussed. Copyright © 2010 American Scientific Publishers. All rights reserved.

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