Abstract
Mg80–xNi20Yx (x = 0–7) alloys were successfully prepared by using the vacuum induction melting method. The structural characterizations of the alloys were performed by using X-ray diffraction, scanning electron microscope, transmission electron microscope and X-ray photoelectron spectroscopy measurements. The effects of yttrium content on the microstructure and hydrogen storage properties of the as-cast alloys were investigated. The alloys are composed of a primary phase of Mg2Ni, lamella eutectic composites of Mg + Mg2Ni, and some amount of YNi3. The YNi3 has completely transformed into in situ formed nanoscale YH2 and YH3, with the formation of Mg2NiH4. Pulverization of the alloy particles was observed during the hydrogen absorption and desorption cycles. However, the phase composition remains unchanged even after 20 hydrogenation cycles. Yttrium addition significantly improved the hydrogen-absorption kinetic performance of the alloy. In addition, pressure-composition-temperature measurements indicated that the entropy and enthalpy changes for the formation and decomposition of MgH2 and Mg2NiH4 gradually decreased with the increase of yttrium content.
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