Study of the hydrogenation of Mg alloy thin film multilayers by Neutron Refraction

Magnesium is a promising material for solid state hydrogen storage applications owing to its high theoretical capacity of 8.2 wt% (H/Mg). Unfavourable thermodynamics coupled with poor kinetics leads to unacceptably slow sorption rates at modest temperatures and pressures. Approaches to increasing the sorption rates include using various formulations of catalytic additions on magnesium surface or using alloy additions within magnesium. The aim of these additions is to increase the kinetics while altering the thermodynamics by making the hydride less stable relative to the metal phase. In this thesis magnetron co-sputtering and sequential sputtering are used to introduce the destabilizing or nanocrystalline catalytic phases. In particular, this thesis shows the hydrogen sorption stages of several binary surface catalysts with particular attention to the superior sorption behaviour of a Pd-Ta binary surface catalyst. The results show that the addition of a Ta layer between the Pd and Mg layers lowers the required sorption pressure by a factor of 10 as compared to a simple Pd-catalysed sample. The sorption behaviour is compared to other bi-layer catalysts that also show promise for increased sorption. (e.g. Pd-Ti bilayer catalyst).;Finally, absorption kinetics are increased through catalytic additions within the Mg bulk alloy. This increased sorption behaviour and absorption character is observed through neutron reflectometry measurements of multilayer thin film multilayer structures. The results show that the absorption occurs within the catalysts layers prior to absorption within the Mg layers; however this observation is not widely seen due to typical instrumentation limitations.;Next, the sorption behaviour of the Mg-Al samples is compared to the sorption behaviour of a pure Mg sample. The result show that Mg-Al tends to absorb homogenously throughout the thin film whereas pure Mg sample tends to absorb from the surface downwards (in a core-shell type of absorption).