Phase components of the sintered Mg-X wt% LaNi5 (X=20-50) composites and their hydrogenation properties

Mg-x wt% LaNi5 (x = 20-50) composite materials were prepared by sintering powder mixtures of magnesium and LaNi5 at 973 K for 1 h. The microstructures were studied using optical microscopy, Xray diffraction and scanning electron microscopy. After sintering, the samples with x = 20 and 30 consisted of Mg, Mg2Ni and LaMg12. As x increased to 40, the La2Mg17 phase started to form. With further increase in x to 50, Mg and LaMg12 vanished, and Mg2Ni and La2Mg17 were the major phases. The phase abundance as a function of composition was determined by Rietveld analysis. It is also found that LaMg12 is not a well-defined stoichiometric compound but exists within a composition range. Compared with pure magnesium, all samples were more easily activated under hydrogen pressure of 5 MPa at 623 K. From the viewpoint of pressure-composition isotherms (P-C isotherms) of hydrogenation, the sintered Mg-x wt% LaNi5 (x = 20-50) composites work as a mixture of pure magnesium and Mg2Ni. (C) 2000 Acta Metallurgica Inc. Published by Elsevier Science Ltd. All rights reserved.