Applications for in-situ neutron diffraction on hydrogen storage materials

In situ diffraction techniques above all, offer the unique opportunity of probing in real time and under experimental conditions the behaviour of the investigated compounds. Especially in-situ neutron diffraction seems to be a preferential choice for the study of hydrogen storage materials, since hydrogen is clearly identified and the structural characterization of the compound can be complete and effective. Phase evolution during hydrogen absorption and desorption cycles and detection of new intermediate phases can be successfully pursued with a considerable improvement in the basic understanding of the material. The use of amide/alkaline hydride mixtures illustrates well such a typical case. In order to obtain a more accurate reaction path for the absorption/desorption processes of magnesium amide (Mg(NH2)2) and lithium hydride (LiH) mixtures, in-situ neutron diffraction techniques have been employed. Experiments were performed at D20/ILL and SPODI/FRMII. The results reveal a common reaction pathway for 1:2, 3:8 and 1:4 magnesium amide:lithium hydride mixtures. Intermediate reaction steps are always observed in both ab- and desorption. The thermodynamic properties of the system at 200oC are not changed by changing lithium hydride stoichiometry. (author)