Oxygen adsorption of molten Ag–Cu eutectic alloy and its associated surface modification

The surface tension of liquid Ag–Cu eutectic alloy has been measured in a wide range of oxygen partial pressures using two different methods: the constrained drop method and the electromagnetic levitation method. In order to investigate the influence of oxygen potential on the surface tension of the Ag–40Cu (at.%) eutectic alloy, the oxygen partial pressure was varied between 8.62 × 10⁻¹⁵ and 2.42 Pa. At low oxygen partial pressure, the surface tension of the Ag–Cu eutectic alloy measured in the temperature range of 1223–1476 K, shows temperature dependence in a good agreement with previously reported results. At higher oxygen partial pressures, the decrease in surface tension is more pronounced and the oxygen adsorption on the surface accordingly increases. Moreover, at high oxygen partial pressure, the oxygen adsorption on the Ag–Cu eutectic alloy was found to be far greater than the expected saturation limit taking into account the theoretically calculated surface concentration of Cu in the Ag–Cu eutectic alloy and the surface excess of oxygen on the molten Cu at saturation. This phenomenon can be explained with a model where the surface of the Ag–Cu eutectic alloy undergoes Cu-substitution at the Ag sites during the oxygen adsorption process.