The interfacial properties between liquid Fe–O alloy and alumina substrates with different purities, 99.9% and 96% Al₂O₃, were measured by the sessile drop method. The interfaces of samples were examined by SEM and EPMA after the experiment.
It was found that the surface tension decreased with increasing oxygen concentration in the iron for both substrates.
The contact angle of 99.9% Al₂O₃ abruptly increased with increasing oxygen concentration at lower oxygen concentrations. These phenomena were attributed to the dissociation of Al₂O₃. Moreover, at higher oxygen concentration, the formation of the dense hercynite was observed at the Fe–O/Al₂O₃ interface, the contact angle slightly decreased with increasing oxygen concentration. For 96% Al₂O₃, a Ca- or Mg-rich layer was observed at the interface at a lower oxygen concentration, the contact angle abruptly increased with increasing oxygen concentration. Whereas, at higher oxygen concentrations, the contact angle rapidly decreased with increasing oxygen concentration. Under these conditions, the formation of hercynite and the penetration of iron into the grain boundaries of Al₂O₃ substrates were observed.