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

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 Mg₆₇Ni₃₃ 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 Mg₆₇Ni₂₈Pd₅ 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.