Structure and hydrogenation features of mechanically activated LaNi5-type alloys

Abstract

The effect of short-term mechanical activation in a ball mill on the thermodynamics of interaction with hydrogen and the structure of intermetallic and hydride phases was studied for a series of AB5 type alloys from the standpoint of their use as filler in metal-polymer membranes. It was found that the activation processing leads, as expected, to a decrease in the size of coherent scattering domains and an increase in the lattice strain, while the phase composition and unit cell parameters remain unaffected. Despite this, there is a significant change in the pressure-composition isotherms, a reduction of the total capacity ad the plateau region. XRD study of the hydride phases evidences smaller volume expansion of the intermetallic crystal lattice at hydrogen absorption for the alloys subjected to mechanical activation. Analysis of the obtained thermodynamic and structural data allows us to consider the mechanically activated LaNi4.8Al0.2 as the most appropriate for low-pressure and low-temperature application in the hydrogen separation composite membranes. La0.7Ce0.3Ni4.5Cu0.5 and LaNi5 with maximum activation treatment of 3 min are more promising for use at elevated pressures.