1 Institute of Materials Technology and Applied Mechanics, Military University
of Technology, Kaliskiego 2, 00-908 Warsaw 49, Poland
2 Department of Mechanical Engineering, University of Waterloo, Waterloo,
Ontario, Canada N2L 2G1
3 Faculty of Materials Science and Engineering, Warsaw University of Technology,
Woiowska141, 02-507 Warsaw, Poland
4 Institute of Chemistry, Military University of Technology, Kaliskiego 2,
00-908 Warsaw 49, Poland
| A nearly single-phase Mg2Ni alloy obtained by ingot metallurgy was mechanically (ball) milled for 20 h in two types of ball mills: Fritsch and Spex with the objective of obtaining nanocrystalline powders suitable for subsequent hydrogenation in gaseous hydrogen. The powders processed in both ball mills are characterized by quite similar average powder particle size which is within the range of 1-30 µm and the average nanograin size of the Mg2Ni phase which is on the order of 7 nm as roughly estimated from the Scherrer formula. However, X-ray diffraction (XRD) spectrum from the Spex powder gives some evidence of partial amorphization of the Mg2Ni phase as opposed to the Fritsch powder. Hydriding tests of both powders investigated in an automated Sieverts apparatus have shown that the Fritsch powder exhibits faster hydriding kinetics than its Spex counterpart. The overall kinetics of hydrogen sorption for the faster absorbing Fritsch powder seems to be roughly in the same range as reported in the literature since it absorbs about 2.7 wt. % of hydrogen after 1800 s (30 min). The differences in the hydriding kinetics between the Fritsch and Spex powders are discussed in terms of the presence of the partially amorphized Mg2Ni phase as well as the presence of higher density of embedded MgNi2 particles in the Fritsch powder which can act as catalysts for hydrogen sorption, differences in the contamination from Fe pick up and MgO impurities content during milling in both powders, difference in the expansion of unit cell volume and mill-dependent different deformation mechanisms of powder particles (e.g. twinning vs. dislocation accumulation). |
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