Phase Equilibria, Crystal Structure and Hydriding/Dehydriding Mechanism of Nd4Mg80Ni8 Compound

作者：Luo, Qun; Gu, Qin-Fen; Zhang, Jie-Yu; Chen, Shuang-Lin; Chou, Kuo-Chih; Li, Qian^*

来源：Scientific Reports, 2015, 5(1): 15385.

DOI：10.1038/srep15385

• HYDROGEN-STORAGE PROPERTIES
• X-RAY-DIFFRACTION
• MG-NI ALLOYS
• HYDRIDING KINETICS
• ND ALLOYS
• CHOU MODEL
• MAGNESIUM
• COMPOSITES
• ABSORPTION
• LA

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 degrees 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) angstrom and c = 15.9170( 2) , 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 degrees C and surface penetration for dehydriding reaction at 291 - 347 degrees 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.

• 出版日期2015-10-16
• 单位上海大学