Phase Transformations in MgH2-TiH2 Hydrogen Storage System by High-Pressure Torsion Process
Phase Transformations in MgH2-TiH2 Hydrogen Storage System by High-Pressure Torsion Process
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DOI：
10.1002/adem.201900027
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发表时间：
2020-01-01
影响因子：
3.6
通讯作者：
Horita, Zenji
中科院分区：
文献类型：
--
作者：
Kitabayashi, Kouki;Edalati, Kaveh;Horita, Zenji
氢化镁（MgH 2）和氢化钛（TiH 2）是固态储氢的两种潜在候选物，但是这些氢化物中的强氢化物形成能不期望地导致它们的高脱氢温度。第一性原理计算表明，MgH 2-TiH 2体系中的亚稳相具有较低的氢结合能，更适合于低温储氢。本研究利用高压扭转（HPT）方法对MgH_2-TiH_2体系进行剧烈塑性变形（SPD），制备亚稳相MgH_2-TiH_2。虽然MgH 2转变为高压正交γ相，但TiH 2即使通过在低温下的HPT处理也不表现出任何α-到-四氢-的相变。通过400 HPT的大应变的应用转向不混溶的MgH 2/TiH 2复合物，导致原子尺度的混合和形成具有亚稳FCC结构和比TiH 2更低的脱氢温度的纳米结构的三元Mg-Ti-H氢化物。
Magnesium hydride (MgH2) and titanium hydride (TiH2) 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 MgH2-TiH2 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 MgH2-TiH2 system to synthesize metastable hydrides. While MgH2 transforms to a high-pressure orthorhombic gamma phase, TiH2 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 MgH2/TiH2 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 TiH2.