Temperature dependence of the chemical potential of hydrogen in the two-phase coexistence region of the palladium–hydrogen system

Abstract

The chemical potential of hydrogen in the coexisting dilute α and hydride α′ phases of palladium–hydrogen has been examined as a function of temperature under conditions where there is essentially no hydrogen transferred between the gaseous and solid phases. The behaviour of Δµ_H is governed by the redistribution of hydrogen between the two coexisting phases following the temperature change. If the chemical potentials of the two phases cannot become equal by transfer of hydrogen within the hysteresis gap, then the hydride phase must either form or decompose. This determines whether the system ends up within the hysteresis gap or on one or other of the plateau branches. This model is developed mathematically and confirmed by experimental results for the palladium–hydrogen system.