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Phase Transformations in MgH 2 –TiH 2 Hydrogen Storage System by High‐Pressure Torsion Process
Author(s) -
Kitabayashi Kouki,
Edalati Kaveh,
Li HaiWen,
Akiba Etsuo,
Horita Zenji
Publication year - 2020
Publication title -
advanced engineering materials
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.938
H-Index - 114
eISSN - 1527-2648
pISSN - 1438-1656
DOI - 10.1002/adem.201900027
Subject(s) - materials science , hydrogen storage , hydride , magnesium hydride , dehydrogenation , metastability , hydrogen , orthorhombic crystal system , tetragonal crystal system , titanium hydride , crystallography , severe plastic deformation , thermodynamics , chemistry , titanium , metallurgy , crystal structure , microstructure , alloy , metal , organic chemistry , physics , catalysis
Magnesium hydride (MgH 2 ) and titanium hydride (TiH 2 ) are two potential candidates for solid‐state hydrogen storage, but strong hydride formation energy in these hydrides undesirably results in their high dehydrogenation temperature. First‐principles calculations show that the metastable hydrides in the MgH 2 –TiH 2 system have low hydrogen binding energy, which makes them more appropriate for low‐temperature hydrogen storage. In this study, severe plastic deformation (SPD) via the high‐pressure torsion (HPT) method is applied to the MgH 2 –TiH 2 system to synthesize metastable hydrides. While MgH 2 transforms to a high‐pressure orthorhombic γ phase, TiH 2 does not exhibit any cubic‐to‐tetragonal phase transformation even by HPT processing at cryogenic temperature. Application of large strains by 400 HPT turns to the immiscible MgH 2 /TiH 2 composite results in atomic‐scale mixing and formation of nanostructured ternary Mg–Ti–H hydride with the metastable FCC structure and lower dehydrogenation temperature than TiH 2 .