Crystallization Process, Structure and Hydrogen Absorption and Desorption Properties of MgxNi10 (x = 20.5-26.5) Alloys with Hypereutectic Composition

Abstract

We have analyzed crystallization process of the Mg_xNi₁₀ (x = 20.5 – 26.5) alloys using phase diagram of Mg-Ni system. Their structure, atomic arrangement and crystal defects were tested by XRD, SEM and HRTEM, respectively. Hydrogenation and dehydrogenation behaviors were measured by pressure-composition-isotherm measurement. The results show that the crystallization processes of the Mg_xNi₁₀ (x = 20.5 and 22.5) alloys are unlike those of the Mg_xNi₁₀ (x = 24.5 and 26.5) alloys, but their room temperature microstructure all contain Mg₂Ni and eutectic structure of Mg₂Ni + α-Mg. The alloys are composed of Mg₂Ni phase and α-Mg phase. The addition of Mg is beneficial to the formation of eutectic structure. The alloys have all good activation property. At a lower temperature, such as 200 and 250 °C, the hydrogen absorption rate and hydrogen saturation ratio are significantly lower than those of the alloy at the higher temperatures, such as 300 and 350 °C. At 350 °C, the hydrogen absorption capacity of the alloy increase and the hydrogen release efficiency of the alloy decreases with the increase of Mg content. The time of 90% of the amount of saturated hydrogen absorption and desorption of the alloys is not more than 10 and 2 minutes, respectively. The hydrogen desorption rate of the Mg_22.5Ni₁₀ alloy in the four investigated alloys is relatively large and up to 7.170 wt.%.min^-1.