A combined experimental and theoretical study was made of H solubility at equilibrium in nanocrystalline Pd. It was found that the elastic interaction between the grain boundaries and the crystal lattice had an important influence upon the adsorption isotherms at small grain sizes. In α-Pd–H (dilute solution), the superficial H density, Γ, at the grain boundaries was positive. This produced a tensile stress and an increase in the H fraction in the lattice (when compared with bulk Pd–H). In α′-Pd–H (concentrated solution), Γ was negative, the stress was compressive and the lattice was H-depleted. Values were reported for the thermodynamic parameters that quantified the forces, and deformation of the grain boundaries. Their values were also of opposite sign for the 2 phases. The results for grain-boundary adsorption isotherms implied an enrichment or depletion within a layer that was much wider than the structural core of the grain boundary.

Grain Boundary Segregation, Stress and Stretch - Effects on Hydrogen Absorption in Nanocrystalline Palladium. C.Lemier, J.Weissmüller: Acta Materialia, 2007, 55[4], 1241-54