Mechanical alloying and hydrogen absorption properties of the Mg–Ni system

• Published in: Journal of alloys and compounds Vol. 267; no. 1; pp. 302 - 306
• Main Authors: Liang, G, Boily, S, Huot, J, Van Neste, A, Schulz, R
• Format: Journal Article
• Language: English
• Published: Lausanne Elsevier B.V 06.03.1998; Elsevier
• Subjects: Applied sciences; Cross-disciplinary physics: materials science; rheology; Exact sciences and technology; Hydrogen storage alloy; Materials science; Materials synthesis; materials processing; Mechanical alloying; Metals. Metallurgy; Mg–Mg 2Ni composite; Physics; Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation; Mg–Mg 2Ni composite; Mechanical alloying; Hydrogen storage alloy; Binary alloys; Hydrogen storage; Nickel alloys; Magnesium alloys; Experimental study; Powder metallurgy; Transition element alloys
• ISSN: 0925-8388; 1873-4669
• DOI: 10.1016/S0925-8388(97)00533-1

The mechanical alloying process of mixed elemental Mg and Ni was investigated. After milling, we found a mixture of Mg and Mg 2Ni in the composition range x>66.67 for Mg x Ni 100− x and a single Mg 2Ni phase at the composition x=66.67. The crystallite sizes of Mg and Mg 2Ni in the as-milled state were 20 and 10 nm, respectively. The Mg 2Ni keeps its nanocrystalline structure when heated to 673 K, whilst Mg grains in the Mg+Mg 2Ni composite grow much more rapidly with increasing annealing temperature. The hydrogen storage properties of these nanocrystalline powders were characterized. During the first absorption cycle, we observed that nanocrystalline Mg 2Ni absorbs hydrogen more rapidly than the two-phase material. However, after activation, the nanocrystalline Mg+Mg 2Ni has better hydriding kinetics at low temperature (423 K) than nanocrystalline Mg 2Ni. This is contrary to what was observed in conventional coarse-grained systems. Possible explanations would be that Mg 2Ni catalyses the hydrogen chemisorption in the composite and that the phase boundaries enhance hydrogen diffusion. The absorption and desorption enthalpies of Mg and Mg 2Ni were evaluated by Van't Hoff plots. The desorption enthalpy increases a little and the absorption enthalpy decreases compared to polycrystalline materials.