Hydriding characteristics of Mg- xwt.%LaNi 5 sintered alloys

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The initial and subsequent hydriding process and hydrogen storage characteristics of Mg-x wt.%LaNi 5 ( x = 10–60) sintered alloys were investigated in comparison with those of pure magnesium, Mg 2Ni and LaMg 12. LaNi 5 addition significantly lowered the temperature at which the hydrogen absorption of magnesium was initiated during the initial hydriding process. The subsequent hydriding rate was also accelerated by the addition of LaNi 5 up to 30%, beyond which the hydriding rate decreased steeply. Microstructural observations revealed that Mg-xwt.%LaNi 5 sintered alloys ( x ⩽ 25.6) consisted of primary magnesium, a eutectic mixture of Mg-Mg 2Ni and LaMg 12, while the alloys (25.6 ⩽ x ⩽ 44.7) consisted of primary Mg 2Ni, LaMg 12 and a eutectic mixture of Mg-Mg 2Ni. The alloys with x ⩾ 44.7 consisted of Mg 2Ni, LaMg 12 and LaNi 5. It was found that the initial and subsequent hydriding rates were closely related to the microstructure and the types of phases present in the alloys. For the initial hydriding process, the presence of LaNi 5 together with the Mg 2Ni phase in the alloy play a crucial role in the acceleration of the initial hydriding process. The subsequent hydriding rates are probably dependent on the amounts of Mg-Mg 2Ni eutectic mixture present in the alloy, whose complicated structure may be effective for hydriding. The pressure-composition isotherms of Mg-xwt.%-LaNi 5 sintered alloys consisted of two plateaux. The pressures of the lower plateau were consistent with those of magnesium and LaMg 12, while the pressures of the higher plateau were consistent with that of Mg 2Ni. It may be concluded that Mg-30wt.%LaNi 5 sintered alloy would be the most suitable material for hydrogen storage of the materials investigated in this study. That is, the initial and subsequent hydriding rates were faster and the hydrogen storage capacity of about 5 wt.% was larger than those of Mg 2Ni.