Thermodynamic factors for controlling the plateau pressure in AB₅ alloys-H SYSTEMS

Abstract

Thermodynamic properties of LaNi_5-x(Mn,Al,MCo)_x(x=0-1.0) alloys-H systems were determined by the measurements of pressure-composition(PC) isotherms. It is well known that the replacement of a fractional part of Ni in LaNi₅ and MmNi₅ alloys by other transition elements causes increase or decrease in the unit cell volume due to the change in size of interstitial holes, which leads to the variation in the stabilization of hydride, corresponding to the plateau pressure[1,2]. In this study, calculated chemical potential of hydrogen was separated into the chemical potential of infinite dilute solution and excess chemical potential of hydrogen[2]. It was found that chemical potential of infinite dilute solution is dominant to control the plateau pressure. This is consistent to the relation between plateau pressure and unit cell volume, indicating that plateau pressure could be estimated from the alloy structure, before absorbing hydrogen.