Aging effects on palladium pressure–composition isotherms during tritium storage

Abstract

Aging effects on palladium pressure–composition isotherms have been studied for tritium storage up to 9 years. Storage properties are remarkably well preserved during aging, and only small modifications of P–c isotherms are observed: a decrease of plateau pressures, and shifts of α and β single phase regions towards greater stoichiometries. For the plateau pressures, the main changes are observed during the first half of the aging period (≈5 years) while phenomena slow down quickly to become almost negligible during further aging. By contrast, the displacements of α and β single phase solubilities are more continuous. These observations can all be correlated to the evolution of the (micro)structural properties. For instance, the 3He generated by tritium decay and retained in the metallic lattice tends to segregate into bubbles, where it has only a weak influence on the structure and consequently on the storage properties. The bubble formation has been demonstrated by transmission electron microscopy (TEM) observations, and the global conservation of structural properties has been established by X-ray and neutron diffraction and by X-ray absorption.