B. Darriet

The hydriding properties of a mechanical alloy with composition Mg-25%Fe☆

A method of mechanical alloying was used to produce an Mg-25%Fe composite hydrogen storage material. The presence of a pure metallic iron surface in contact with the magnesium leads to the promotion of the dissociative adsorption of hydrogen and the hydrogenation of Mg-25%Fe begins at the maximum rate even in the first cycle of hydriding. The activation of the mechanical alloy is completed by the third cycle of hydriding. The process of formation of Mg2FeHx is also studied.

Dehydriding kinetics in the Mg2Ni-H2 system

Abstract The dehydriding kinetics of the Mg2Ni-H2 system are studied between 576 and 610 K under 1.0–3.0 bar H2. A simple relation between the variation in the interfacial area of the reaction and the reacted fraction cannot be given since the activated Mg2Ni particles have irregular shapes, a large sive distribution, and since they are porous. In order to eliminate the influence of the variation in the interfacial area of the reaction on the dehydriding rates, the dependences of the dehydriding rates on the hydrogen pressure and the temperature are investigated in the same ranges of reacted fraction, where the reaction-interfacial areas are considered nearly evual.

Influence de la substitution du cuivre au nickel dans Mg2Ni sur le stockage de l'hydrogène

Resume Letude cristallochimique du systeme Mg 2 Niue5f8Mg 2 Cu a permis de mettre en evidence une solution solide Mg 2 Ni 1− x Cu x (0 x ⩽ 0,85) de type Mg 2 Ni. Laction de lhydrogene sur cette solution solide entraine simultanement la formation des phases MgH 2 , Mg 2 NiH 4 et MgCu 2 qui ont ete identifiees par analyse radiocristallographique. Le mecanisme dhydruration a ete precise par le trace dune isotherme pour x = 0,50. Labsorption et la desorption de lhydrogene par Mg 2 Ni 1− x Cu x seffectuent a des vitesses voisines de celles de Mg 2 Ni. La substitution partielle du cuivre au nickel dans Mg 2 Ni permet dobtenir des alliages dont les hydrures ont des temperatures de dissociation de lordre de 225 °C pour une pression dhydrogene d1 atm.

XRD, EXAFS and XANES studies of new bismuth cubic or pseudo-cubic perovskite-type phases

Abstract New bismuth cubic or pseudo-cubic perovskite type phases have been prepared by solid state reactions. Cubic symmetry ( F m 3 ¯ m ) was observed for Ba2(AxBi2−x)O6−x/2 (A = Sr2+, Ca2+) compounds, except for Ba2Sr1/3Bi5/3O5.83 compositions where the structure crystallizes with monoclinic symmetry (I2/m). Creation of oxygen vacancies contributing towards a gradual contraction of the unit cell, are competing with Ca2+ or Sr2+ substitutions regarded as the partial replacement of Bi3+ leading to an increase of the unit-cell. The XRD patterns of the Ba2(RuxBi2−x)O6 (x = 1/2, 2/3) pseudo-cubic solid solutions are indexed using a body-centered monoclinic cell (I2/m), the unit cell volume decreasing as the Ru content increases. X-ray absorption spectroscopy measurements of Bi LIII near edge structure and EXAFS oscillations have revealed evidence of mixed valencies in these compounds and have given complementary and new information about the environment of bismuth which can be five or six-fold coordinated to oxygen atoms. The Bi LIII edges exhibit a continuous evolution with increasing Ca or Sr doping level or with lowering Ru doping. The Bi LIII edges are dominated by two main features due to 2p3/2 ↦ 6d and 2p3/2 ↦ 6s transtions due to the unfilled 6s states of Bi5+ only. Such a feature which is indicative of the absence of the lone pair allows an unambiguous determination of the highest valence states of these elements and to discriminate between Bi3+ and Bi5+. Detailed analysis of XAFS reveals that with increasing Ca or Sr doping, or with lowering Ru doping, the average Bi−O distance decreases continuously, in good agreement with XANES and XRD analysis.

A new ternary hydride: CsCaH3

Cristallisation dans le systeme orthorhombique, structure type GdFeO 3 . Precision des conditions de stabilite thermique

STUDY OF THE CONTAMINATION OF THE CERIUM‐MAGNESIUM (CEMG12) ALLOY BY NITROGEN, OXYGEN AND WATER VAPOR. USE FOR STORING HYDROGEN

Durch volumetrische Bestimmung der Wasserstoff-Absorption uber mehrere ( v 150) Absorptions- Desorptionszyklen (i.a.