The surface of copper-nickel alloy films: II. Phase equilibrium and distribution and their implications for work function, chemisorption, and catalysis

Abstract

Free energy calculations show that in the copper-nickel system there is a miscibility gap at low temperatures. The composition of the phases that are characterized by minima of the free energy agrees with experimental data on alloy films prepared at low temperatures by interdiffusion of the two components. From data on the diffusion it is inferred that for compositions within the miscibility gap, equilibrated films consist of crystallites each of which contains a kernel of almost pure nickel, enveloped in a skin of a copper-rich alloy. As the composition of either phase is independent of the over-all composition, the surface properties of these alloys are constant. This is confirmed by experimental data on the work function. The model also appears to be consistent with results on the catalytic activity and the heat of adsorption of hydrogen on granular alloy catalysts, as reported by various investigators.