Thermodynamics of the solution of hydrogen in LaNi 5 at small hydrogen contents

Abstract

Partial thermodynamic parameters for the solution of hydrogen in LaNi 5 have been determined by p-c-T methods on unactivated bulk samples of LaNi 5. The relative partial molar enthalpy of solution of hydrogen, at infinite dilution of hydrogen, is −33,9 kJ (g atom H) −1 (~425 K). This is more exothermic than the heat of absorption corresponding to the formation of the hydride phase from the hydrogen-saturated intermetallic compound. The partial molar enthalpy of solution becomes more endothermic with hydrogen content in the region of solubility in the pure intermetallic compound. The partial thermodynamic quantities at infinite dilution have been found to vary with the stoichiometry of the LaNi 5+ x where x varies from −0.2 to + 0.5. The partial molar enthalpy of absorption is most exothermic for the stoichiometric compound.