Effect of rapid quenching on the microstructures and electrochemical characteristics of La0.7Mg0.3Ni2.55-xCo0.45Alx (x=0-0.4) electrode alloys

A new type of hydrogen storage alloy La0.7Mg0.3Ni2.55-xCo0.45Alx (x=0, 0.1, 0.2, 0.3, 0.4) with a PuNi3-type structure (R-3m) were prepared by casting and rapid quenching. The effects of the rapid quenching on the microstructures and electrochemical performances of the specimen alloys were investigated in detail. The results obtained by XRD, SEM and TEM show that the as-cast and quenched alloys have a multiphase structure, including the (La, Mg)Ni-3 phase, the LaNi5 phase and the LaNi2 phase. The rapid quenching had an inappreciable influence on the phase composition of the alloys, but it obviously changed the phase abundance of the alloys. The rapid quenching can significantly improve the compositional homogeneity and markedly decrease the grain size of the alloys. The results obtained by the electrochemical measurements indicate that the rapid quenching obviously enhanced the cyclic stability of the alloys, but it decreased the discharge capacity and activation capability of the alloys. (C) 2006 Elsevier Inc. All rights reserved.