DEVELOPMENT OF A PROCESS FOR DIRECTLY PRODUCING Zr-Ni-Mn ALLOY POWDERS FOR HYDROGEN STORAGE BY METALLOTHERMIC REDUCTION METHOD

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Aiming at the development of an efficient process to make Zr-Ni-Mn alloy powders directly from the oxide resources of zirconium and manganese by using metallic calcium as a reductant, the hydrogen-absorbing and -desorbing properties of the synthesized alloys and the mechanism of formation of the alloy were studied.Firstly, more than 50 kinds of Zr-Ni-Mn alloys were synthesized by arc-melting and their properties were investigated in relation to the microstructure and the compositions. It was clarified that the alloys with a single phase just before separating into two-phases have most favorable properties for hydrogen storage, with the compositions of 42.2%Zr, 29.9%Ni and 27.9%Mn or 44.4%Zr, 34.3%Ni and 21.3%Mn.Secondly, the alloy powders with the compositions of 44.4%Zr, 34.3%Ni and 21.3%Mn were prepared by the metallothermic reduction method. It was found that the alloys were formed through a heterogeneous reaction between nickel in the liquid Ni-Ca alloy phase and the solid Zr and Mn phases. This mechanism was quite defferent from that in making Ni-rare earth alloys by the same method. The properties of the produced alloys for hydrogen storage was found to be a little inferior to those of the alloys produced by the arc-melting. It was considered that the properties must improve by removing the oxide layr formed on the alloy powder which makes the transit of hydrogen atom difficult.