Effects of rapid quenching on microstructure and electrochemical performances of La-Mg-Ni system hydrogen storage alloys

The La-Mg-Ni system (PnNi(3)-type) electrode alloys La2Mg(Ni0.85Co0.15)9B(x) (x = 0, 0.1, 0.2) were prepared by casting and rapid quenching. The microstructures and electrochemical performances of the as-cast and quenched alloys were determined and measured. The effects of boron content and quenching rate on the microstructures and electrochemical properties of the alloys were investigated in detail. The results show that the as-cast and quenched alloys are composed of the (La, Mg)Ni-3 phase (PuNi3-type structure), the LaNi5 phase and the LaNi2 phase. A trace of the Ni2B phase exists in the as-cast alloys containing boron, and after the as-cast alloys are quenched, the Ni2B phase in the alloys nearly disappears. The relative amount of each phase in the alloys depends on the composition of the alloys and the quenching rate. The capacity of the alloys without boron monotonously decreases with the increase of the quenching rate, but for the alloys containing boron, the capacities have a maximum value with the variety of the quenching rate. The cycle lives of the as-quenched alloys increase with the increase of the quenching rate. The activation performances of the as-cast and quenched alloys are excellent.