Interfacial tensions between liquid dilute Fe-Si-O alloys and CaO-SiO₂-FeO slags were determined using the sessible slag drop on the surface of the metal. This drop was maintained by a basket of thin Pt and PtRh (20%) wires, which enabled to obtain both equilibrium and nonequilibrium interfacial tensions, preventing the two liquids from the contamination from the container. Results obtained are as follows:
(1) As a whole, an increase in oxygen content of the metal substantially lowers the equilibrium interfacial tension σ⁰_ms and also nonequilibrium one σ⁰_ms.
(2) Dependencies of σ0ms, a nonequilibrium value obtained at the beginning stage of iron transfer from the metal to the slag, on the oxygen content of the metal and temperature differ from those of σ^e_ms. These differences increase in magnitude with an increase in the oxygen content of the metal.
(3) An increase in FeO content of the slag substantially lowers σ⁰_ms, a nonequilibrium value obtained at the biginning stage of iron transfer from the slag to the metal. This effect of FeO increases markedly with an increase in the oxygen content of the metal.