HYDROGEN IN METAL VACANCIES

The hydrogen solubility in beta-NiAl was measured using a quench and analyse technique. Pressures up to 50 bar were used. In this compound there exists a large concentration of vacancies on the Al-rich side of stoichiometry. The stoichiometric alloy was found to have the lowest H solubility. Both the partial molar enthalpy and the standard relative partial entropy of H are lowest at the stoichiometric composition. The observed compositional variation in the standard partial entropy is much too large to be attributed to vibrational effects. A plausible explanation in terms of configurational effects is proposed involving the vacancies in the Al-rich alloys as sites for H-absorption.