A comparative study of NbF5 catalytic effects on hydrogenation/dehydrogenation kinetics of Mg-Zn-Ni and Mg-Cu-Ni systems

Abstract

In this study, Mg85Zn5Ni10/Mg85Cu5Ni10 – x wt% NbF5 (x = 0, 2, 4) alloys were synthetized via vacuum induction smelting and high energy ball milling. The different NbF5 catalytic effects and mechanisms on microstructure, hydriding/dehydriding kinetics of Mg85Zn5Ni10/Mg85Cu5Ni10 alloys were discussed in detail. The results prove that NbF5 promotes the formation of cracks and pulverization on the alloy particles and to producing more numbers of grain boundaries, amorphous-nanocrystalline and dislocations which are beneficial for H2 diffusion. The dehydrogenation activation energies are reduced to 82.367 and 87.076 from 109.830 and 116.767 kJ/mol respectively for Mg85Zn5Ni10 and Mg85Cu5Ni10 by 4 wt% NbF5. NbF5 decomposes in Mg85Cu5Ni10 system, but not in Mg85Zn5Ni10 system. The stable MgZn2 and transformation between Mg2Cu and MgCu2 may explain the decomposition of NbF5 in Mg-Cu-Ni systems. NbF5 can ameliorate the hydriding/dehydriding kinetics of Mg85Zn5Ni10 and Mg85Cu5Ni10 systems significantly. NbF5 does not change the thermodynamic properties of Mg85Zn5Ni10/Mg85Cu5Ni10 alloys.