Interfacial phenomena between immiscible liquids are interesting from scientific and technological viewpoints in many fields. In the field of steel manufacturing, interfacial phenomena between molten oxide and liquid Fe are important for process control. Therefore, the interfacial tension between them is required for using process control simulations. From the background, we have performed interfacial tension measurement using the surface oscillation of compound droplets by molten oxide and liquid Fe in the electrostatic levitation furnace (ELF) in ISS. On ground conditions, it is difficult to form a compound droplet by molten oxide and liquid Fe from the large difference in their density; however, under microgravity without the density difference compound droplets can be easily formed. Using the core-shell droplet, we can apply the modified drop oscillation analysis by two interface conditions in liquid-liquid and liquid atmospheres. From the analytical solution of two interface drop conditions, the normal mode of the core-shell droplet has two separate eigenfrequencies in fundamental oscillation. From the two eigenfrequencies, we can calculate the interfacial tension value ¹⁾. Our onboard experiments of observing compound drop oscillation phenomena using ELF have been performed since October 2022. We succeeded in observing the surface oscillation phenomena of compound droplets by molten oxide (SiO2:CaO:Mn3O4:TiO2:Fe2O3= 25:7:20:18:30 mass%) and liquid iron in Ar atmosphere. However, during the observation of oscillation phenomena, an increase in droplet volume was observed (Fig. 1). This may be due to the oxidation of liquid Fe at the interface with the molten oxide. When oxidation occurs, the radius ratio of the shell to the core changes, which affects the interfacial tension measurement. Furthermore, the density and surface tension of the shell molten oxide also change due to oxidation. Therefore, it is necessary to investigate the changes in the density and surface tension of the molten oxide during oxidation. For this reason, we measured the density and surface tension of the molten oxide when liquid iron was dissolved into the molten oxide by oxidation using the aerodynamic levitation method on the ground. From these measurements, we discuss the oxidation of liquid iron at the interface between the molten oxide.

References:

1. M. Watanabe et al., Int. J. Microgravity Sci. Appl., 33 (2016) 330212.