2006 Volume 47 Issue 8 Pages 1890-1893
Mg-based Laves phase alloys (Mg0.7M0.3)Ni2, where M elements were Ca, La, Ce, Pr, Nd and Gd were successfully developed. The alloys can be synthesized by a conventional induction melting and annealing method from intermetallic compounds MgNi2 and MNi2 as a source of Mg, Ni and M elements. The crystal structures of the major phases of annealed (Mg0.7M0.3)Ni2 alloys were C15-type for M=Ca and C15b-type for M=La, Ce, Pr, Nd and Gd Laves structures, respectively. In the alloys except M=Ce, hydrogenation and dehydrogenation reversibly occurred. The maximum hydrogen contents of the alloys are 1.2–1.6 mass% (H/M:0.6–0.8) under hydrogen pressure of 5 MPa at 243–273 K. As the results of measurements of p-c isotherms, in the case of the M=Pr and Nd, two step plateaus were clearly observed. After a few hydrogenation/dehydrogenation cycles, the alloys kept C15-type or C15b-type Laves structures without hydrogen-induced amorphization, disproportionation and decomposition.