Influence of oxygen partial pressure on surface tension of molten silver

Influences of oxygen partial pressure, PO₂, of ambient atmosphere and temperature on surface tension of molten silver were experimentally investigated by an oscillating droplet method using an electromagnetic levitation furnace. We successfully measured surface tension of molten silver within a very wide temperature range of over 550 K under a well-controlled PO₂ atmosphere. Surface tension of pure melt surface, σ^p, was determined without any contamination such as oxygen adsorption and the reaction between the melt and a measurement device at a PO₂ of less than 10^-12 Pa. When the PO₂ was controlled at 10² Pa, the "boomerang shape" temperature dependence of surface tension was experimentally observed; surface tension was increased and then decreased with increasing temperature. From these experimental data, the temperature dependence of equilibrium constant for oxygen adsorption was determined using the Szyszkowski equation. We successfully expressed the surface tension of molten silver as functions of both PO ₂ and temperature. Furthermore, the changes in enthalpy and entropy for oxygen adsorption on molten silver were also estimated.