Increase in thermal stability of Mg62Ni33Ca5 amorphous alloy by absorptionof hydrogen

It was found that an amorphous Mg62Ni33Ca5 alloy absorbs a large amount of hydrogen at 323 K and the hydrogen content is much larger than that of the corresponding crystalline alloy. The maximum absorption concentration of hy drogen at 323 K is 2.3 mass% in the amorphous phase and 1.3 mass% in the cr ystalline state. The Mg-based amorphous alloy with 2.3 mass%H-2 crystallize s through the process of Am --> Am'+Mg2Ni --> Mg2Ni+Mg2Ca+MgNi2+Mg2NiH4. Th e crystallization process is different from that (Am --> Mg2Ni+Mg2Ca+MgNi2) of the as-quenched amorphous phase. The onset temperature and the complete d temperature for crystallization is 453 and 532K, respectively, for the as -quenched amorphous alloy and 475 and 572 K, respectively, for the amorphou s phase containing 2.3 to 3.0 mass%H-2. The absorption of hydrogen causes a significant increase in the thermal stability of the amorphous phase, pres umably because of the necessity of a larger amount of hydrogen for the crys tallization of the remaining amorphous phase which is coexistent with Mg2Ni . The retardation of the crystallization reaction of the Mg-based amorphous ahoy by absorption of hydrogen is encouraging for future application to hy drogen-storage materials. It is concluded that the hydrogen can be used to control the thermal stability and crystallization process of Mg-based amorp hous alloys.