title: Phase Equilibria, Crystal Structure and Hydriding/Dehydriding Mechanism of Nd4Mg80Ni8 Compound.
abstract: In order to find out the optimal composition of novel Nd-Mg-Ni alloys for hydrogen storage, the isothermal section of Nd-Mg-Ni system at 400 °C is established by examining the equilibrated alloys. A new ternary compound Nd4Mg80Ni8 is discovered in the Mg-rich corner. It has the crystal structure of space group I41/amd with lattice parameters of a = b = 11.2743(1) Å and c = 15.9170(2) Å, characterized by the synchrotron powder X-ray diffraction (SR-PXRD). High-resolution transmission electron microscopy (HR-TEM) is used to investigate the microstructure of Nd4Mg80Ni8 and its hydrogen-induced microstructure evolution. The hydrogenation leads to Nd4Mg80Ni8 decomposing into NdH2.61-MgH2-Mg2NiH0.3 nanocomposites, where the high density phase boundaries provide a great deal of hydrogen atoms diffusion channels and nucleation sites of hydrides, which greatly enhances the hydriding/dehydriding (H/D) properties. The Nd4Mg80Ni8 exhibits a good cycle ability. The kinetic mechanisms of H/D reactions are studied by Real Physical Picture (RPP) model. The rate controlling steps are diffusion for hydriding reaction in the temperature range of 100 ~ 350 °C and surface penetration for dehydriding reaction at 291 ~ 347 °C. In-situ SR-PXRD results reveal the phase transformations of Mg to MgH2 and Mg2Ni to Mg2NiH4 as functions of hydrogen pressure and hydriding time.
authors.affiliation: State Key Laboratory of Advanced Special Steels, Shanghai University, Shanghai 200072, China.
authors.forename: Qun
authors.initials: Q
authors.lastname: Luo
authors.affiliation: Australian Synchrotron, 800 Blackburn Rd, Clayton 3168, Australia.
authors.forename: Qin-Fen
authors.initials: QF
authors.lastname: Gu
authors.affiliation: State Key Laboratory of Advanced Special Steels, Shanghai University, Shanghai 200072, China.
authors.forename: Jie-Yu
authors.initials: JY
authors.lastname: Zhang
authors.affiliation: State Key Laboratory of Advanced Special Steels, Shanghai University, Shanghai 200072, China.|CompuTherm, LLC, Madison, WI 53719, USA.
authors.forename: Shuang-Lin
authors.initials: SL
authors.lastname: Chen
authors.affiliation: State Key Laboratory of Advanced Special Steels, Shanghai University, Shanghai 200072, China.
authors.forename: Kuo-Chih
authors.initials: KC
authors.lastname: Chou
authors.affiliation: State Key Laboratory of Advanced Special Steels, Shanghai University, Shanghai 200072, China.|Institute of Genomic Material, Shanghai University, Shanghai 200444, China.
authors.forename: Qian
authors.initials: Q
authors.lastname: Li