Phase components of the sintered Mg– x wt% LaNi 5 ( x=20–50) composites and their hydrogenation properties

Abstract

Mg– x wt% LaNi 5 ( x=20–50) composite materials were prepared by sintering powder mixtures of magnesium and LaNi 5 at 973 K for 1 h. The microstructures were studied using optical microscopy, X-ray diffraction and scanning electron microscopy. After sintering, the samples with x=20 and 30 consisted of Mg, Mg 2Ni and LaMg 12. As x increased to 40, the La 2Mg 17 phase started to form. With further increase in x to 50, Mg and LaMg 12 vanished, and Mg 2Ni and La 2Mg 17 were the major phases. The phase abundance as a function of composition was determined by Rietveld analysis. It is also found that LaMg 12 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% LaNi 5 ( x=20–50) composites work as a mixture of pure magnesium and Mg 2Ni.