Structural and hydriding properties of the Mg-Ni-H system with nano- and/or amorphous structures

Structural properties of the Mg-Ni alloys have been extensively investigated to improve their hydriding properties. The alloys Mg-x at.%Ni (x = 33, 38, 43 and 50) with different nanometer-scale structures were successively synthesized by mechanical grinding of Mg2Ni with Ni. Nanostructured Mg2Ni (n-Mg2Ni) was obtained by grinding only Mg2Ni (x = 33). Amorphous MgNi (a-MgNi) was partially formed by grinding of Mg2Ni with additional Ni (x = 38 and 43), and was homogeneously formed in equivalent composition (x = 50). The hydriding temperatures decrease from 440 K for x = 33 to 373 K for x = 50 with increasing the Ni amounts. The electrochemical P-c isotherm measurements revealed that there is obviously the miscibility gap (plateau) pressure higher than 10(-4) Wa at ambient temperature even in the amorphous phase. The coordination numbers and interatomic distances of the Mg-D and Ni-D correlations in the a-MgNi-D show that deuterium occupies the interstitial tetrahedral site composed of nearly 2Mg-2Ni. The interatomic distances continuously decrease with increasing Li amounts in LixMgl-xNi-H (x = 0, 0.25 and 0.50).