HYDROGEN SORPTION PROPERTIES OF INTERMETALLIC COMPOUNDS La3-xMgxNi9

Abstract

To increase the hydrogen mass in intermetallides of type LaNi 3 proposed to replace part of the La on Mg. Alloys of composition La 3- x Mg x Ni 9 ( x = 1, 1.1 and 1.2) were prepared. For this first lanthanum-nickel alloys were obtained by arc melting of mixtures of high purity La and Ni in an atmosphere of argon. These alloys were pulverized in a planetary ball mill with the addition of the necessary amount of the magnesium powder. Then the resulting homogeneous mixture was compressed into tablets, wrapped in tantalum foil, placed in a steel pipe and a homogenization annealing was performed at 950 °C for 6 hours. The thus prepared alloys consisted of 70–80 wt.% of the intermetallic compound phase with the structural type PuNi 3 and impurity phases La 4 MgNi 19 and LaNi 5 . The hydrogen sorption properties of intermetallic compounds prepared were studied. It was established that the isotherms La 3- x Mg x Ni 9 – H 2 have one plateau of phase transition, indicating the formation of only one hydride phase with hydrogen content of 1.58 wt.% (La 2 MgNi 9 H x ), 1.52 wt.% (La 1.9 Mg 1.1 Ni 9 H x ) and 1.5 wt.% (La 1.8 Mg 1.2 Ni 9 H x ). At that the equilibrium pressure is increased by rise the magnesium content in the sample. The variations in the enthalpy at dehydrogenation are calculated and it is established the rise of the thermal effect of the reaction with increasing magnesium content.