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Stockage de l’hydrogène par des mélanges mécanochimiques à base de magnésium : Étude de composés intermétalliques ternaires à base de bore (structure et essais d’hydrogénation)

Abstract : The aim of this study was the comprehension of hydrogen storage mechanisms and theimprovement of storage capacity in (1) magnesium and (2) boron based intermetallic compounds.(1) Magnesium powders with 10 wt.% magnesium oxide were milled using a planetary ball mill, byreactive mechanical grinding under hydrogen atmosphere (10 bar) for 10 hours, varying two parameters:the milling speed and the number of balls used (i.e. the powder-to-ball weight ratio). It appears that thepowders milled at 250 rpm using 17 balls (ratio 1: 13) have superior performances in terms of: particlesize, MgH2 content after milling, specific surface area and hydrogen absorption/desorption kinetics. Wehave verified that the magnesium oxide has a significant effect on grain growth, delaying it. Calculation ofthe activation energies and study of the kinetics showed that magnesium oxide does not play a catalyticrole for hydrogen sorption.(2) The compounds synthesized in the ternary systems La-TM-B, Gd-TM-B and Y-TM-B (TM=Ni,Fe, Co) were studied in terms of their crystal structure, chemical composition and hydrogen sorptionproperties. Most of the compounds obtained in these systems crystallize with a CeCo4B-type structure,with lattice parameters close to those of the compound GdNi4B. A total replacement of Ni by Fe and/or Cois sometimes possible, meaning that a total solid solution exists between RENi4B and REFe4B or RECo4B.Also, the boron is assumed to partially occupy two different crystallographic sites, although only one ofthese is mainly occupied by boron. The new phase GdNi2.5B2.5 was also observed in this study for the firsttime. In addition, a pseudo-binary phase GdB3 is observed. Finally, it is reported that only the compoundLaNi4B absorbs hydrogen, albeit irreversibly.
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Liv Pall. Stockage de l’hydrogène par des mélanges mécanochimiques à base de magnésium : Étude de composés intermétalliques ternaires à base de bore (structure et essais d’hydrogénation). Autre. Université Sciences et Technologies - Bordeaux I, 2012. Français. ⟨NNT : 2012BOR14573⟩. ⟨tel-00796217⟩

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