Evaluating Composition Dependence in Surface Tension of Si-Ca-Na-O-F Reciprocal Oxide-fluoride Melts

摘要

Surface tension of molten ionic mixtures such as slag is an important physical property related directly to various surface or interfacial phenomena in high-temperature industrial processes. In particular, surface tension of oxide-fluoride melts is of interest to understand interfacial phenomena in continuous casting in steelmaking. However, the composition dependence of surface tension in reciprocal ionic melts has not been well understood because of its complexity related to the reciprocal reaction between input components in the melt. In this study, we measured the surface tension of reciprocal oxide-fluoride melts in a Si-Ca-Na-O-F multicomponent system, to evaluate its composition dependence. We used a maximum bubble pressure method to determine the surface tension of these melts with high accuracy. Our results indicate that (1) the surface tension of the SiO_2-CaO melt decreases by NaF addition more steeply than by Na_2O addition, and (2) the surface tension of the SiO_2-CaO-CaF_2 melt decreases with Na_2O addition but depends on NaF formation because of the reciprocal reaction CaF_2 + Na_2O = CaO + 2 NaF. When this reaction is taken into account, the surface tension of the SiO_2-CaO-CaF_2-Na_2O melt matches that of the SiO_2-CaO-NaF melt with increased CaO concentration from the above melt composition.