Dresden 2006 – wissenschaftliches Programm

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MM: Metall- und Materialphysik

MM 15: Hydrogen in Metals II

MM 15.2: Vortrag

Dienstag, 28. März 2006, 12:00–12:15, IFW D

Catalytic effect of oxides for decomposition of magnesium hydride explained by the gateway model. — •Andreas Borgschulte and Rüdiger Bormann — GKSS-Research Center, Geesthacht GmbH, WTP, building 59, Max-Planck-Straße 1, 21502 Geesthacht

The kinetics of the reversible reaction of hydrogen gas with magnesium forming MgH₂ is enhanced significantly by the addition of transition metals oxide catalysts and by using nanostructured powders. Hydrogen absorption and desorption properties of such systems were studied by high pressure differential scanning calorimetry (DSC) under hydrogen atmosphere, from which the heat of hydride formation and decomposition of magnesium hydride is revealed. We find an additional, slightly destabilized phase, which is formed within the first desorption. Its amount depends on the degree of nanostructuring and the used additive. The phase is attributed to destabilized magnesium hydride near grain boundaries. It is the intermediate step before the more stable, stoichiometric MgH₂-phase is formed. Thus the phase acts as a gateway for de-hydrogenation of MgH₂. The results correspond to neutron diffraction measurements, in which a MgH_x<<2 was found [1].

[1] H. Gijs Schimmel, Jacques Huot, Laurent C. Chapon, Frans D. Tichelaar, and Fokko M. Mulder, J. Am. Chem. Soc. 127, 14348 (2005).