Thermodynamic study of adsorption in liquid metal-oxygen systems

The influence of oxygen on the surface tension of pure liquid metals has been investigated up to the bulk saturation concentration. Two thermodynamic models are proposed to describe the surface tension isotherm. Up to the concentration corresponding to the maximum adsorption (x) a Fowler-Guggenheim modified isotherm describes, correctly, the experimental surface tension isotherms for various systems. The adsorption energy is shown to depend on bulk thermodynamic quantities and on a surface-composition dependent term. A "surface structure coefficient" is also introduced in order to take into account the stoichiometries of surfaces compounds. For bulk compositions ranging from x to saturation, the application of Gibbs' adsorption law, with fixed values of the absolute adsorptions, is able to take into account the experimental findings. On the basis of this treatment, some general rules are suggested, that allow x and the corresponding ? value to be estimated for unknown systems. © 1988.