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

The alloys Mg-x at.%Ni (x = 33, 35, 43 and 50) with different nanometer-scale structures were successively synthesized by mechanical grinding of Mg2Ni mixed with various amounts of additional Ni, and the relations between their structural and hydriding properties were investigated in detail. The total hydrogen contents in these alloys increase from 1.7 mass% for x = 33 to 2.2 mass% for x = 43 and 50. This result is explainable by estimating both the volume fractions and the maximum hydrogen contents of three regions in each alloy; the intra-grain region of nanostructured Mg2Ni, its inter-grain region, and the amorphous MgNi region. The dehydriding temperature lowers down to 373 K in the alloy composed of only the amorphous MgNi region, while the dehydriding kinetics of the alloy composed of the above three regions are faster than those of only the amorphous MgNi region. (C) 1997 Acta Metallurgica Inc.