Reactive powder metallurgy

In the field of hydrides (IICE – MCMF group), alkali borohydrides are of particular interest for hydrogen storage due to their high hydrogen storage capacity (ex. LiBH4 contains 18.4 wt% H2). The main drawback is their stability which prevents reversibility in moderate temperature and pressure conditions. Thermodynamical destabilization can be achieved through reactive hydride composites which consist on an intimate mixture of alkali borohydride and a metal hydride. The formation of an intermediate phase lowers the formation enthalpy in comparison with pure borohydride. We focus our study on the system LiBH4- MgH2, and in particular on the role of activators on the reversibility and kinetics of the reaction : 2 LiBH4 + MgH2 ↔ 2 LiH + MgB2 + 4 H2

[bleu marine]In situ synchrotron X Ray thermodiffractogram of 2 LiBH4-MgH2 during dehydrogenation[/bleu marine]

On the other hand, to produce performing alloys for H storage, reactive ball milling is used to prepare metallic materials with metastable phases while severe plastic deformation techniques (ECAP, cold rolling) allow to control the microstructure required to improve H-sorption kinetics at low temperatures and structural stability of Mg-based hydrides.

[bleu marine]ECAP (Equal Channel Angular Pressing) set-up[/bleu marine]

Finally, extrinsic properties of magneto-caloric materials can be improved by nano-structuring In the case of La(Fe,Si)13 compounds it can be achieved by the use of techniques such as powder atomization or melt spinning.

[bleu marine]TEM observation of vacancy coalescence in the dislocation-rich region (pore size=50nm)[/bleu marine]
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