Thermal stabilities and discharge capacities of melt-spun Mg–Ni-based amorphous alloys

Abstract

Mg–Ni–M (M=Ca, La or Pd) ternary alloys were synthesized by the melt-spinning technique. All as-solidified alloys possessed an amorphous single phase by the additional effect of the third element, though it was difficult to obtain an amorphous Mg 67Ni 33 binary alloy by melt-spinning. We examined the thermal stability and electrochemical cyclic life property of the ternary amorphous alloys. The crystallization temperature of the amorphous alloys increases with increasing M content. All the alloys except Mg 67Ni 28Pd 5 examined in the present study maintain the amorphous structure even after hydrogen absorption at 373 K for Mg–Ni–Ca and Mg–Ni–Pd and at 423 K for Mg–Ni–La. The crystallization temperature increases by absorbing hydrogen, indicating that the alloys are thermally stabilized by hydrogen absorption. In the electrochemical cyclic life measurements up to five cycles, the Mg–Ni–Pd amorphous alloys exhibit high discharge capacities ranging from 100 to 400 mA h/g as well as small cyclic life degradation tendency, though the Mg–Ni–Ca and Mg–Ni–La amorphous alloys possess small discharge capacities of 10–100 mA h/g with significant cyclic life degradation. It is thus concluded that the good cyclic life property of the amorphous hydrogen storage alloys can be obtained by application of the melt-spinning technique to Mg-based alloys with appropriate alloy compositions.