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

Abstract

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 2 O addition, and (2) the surface tension of the SiO 2 -CaO-CaF 2 melt decreases with Na 2 O addition but depends on NaF formation because of the reciprocal reaction CaF 2 + Na 2 O = CaO + 2 NaF. When this reaction is taken into account, the surface tension of the SiO 2 -CaO-CaF 2 -Na 2 O melt matches that of the SiO 2 -CaO-NaF melt with increased CaO concentration from the above melt composition.KEY WORDS: surface tension; reciprocal ionic mixture; oxide-fluoride slag; composition dependence; maximum bubble pressure method.

Viscosity of Na–Si–O–N–F Melts: Mixing Effect of Oxygen, Nitrogen, and Fluorine

“…In the relatively low SiO 2 region ( < 67 mol%), Sasaki et al 52) concluded that fluorine is mainly present as free-fluorine in the Na 2 O-SiO 2 -NaF system by Raman spectroscopy and MD simulation. This tendency was also found in the physical properties, i.e., electrical conductivity 78) and surface tension, 79) of Na 2 O-SiO 2 -NaF melts with relatively lower SiO 2 .…”

Viscosity Estimation of Multicomponent Slags of the CaO–SiO2–Al2O3–FexO System Based on Microstructure Analysis

“…Some studies , indicated that temperature might affect melt structure, but previous experiment showed that the structures of CaO–SiO 2 –Al 2 O 3 –Fe x O slags changed only slightly with the temperature over a range of 1673–1873 K. Hence, the influence of temperature on the oxygen bond database can be ignored. All the oxygen bond values corresponding to the slag with a specific composition in any temperature of 1673–1873 K can be obtained from the database.…”

“…where a i and b i are the constants corresponding to the binary silicate melt composed of SiO 2 and i, which can be determined by correcting the viscosity data of the CaO−SiO 2 −Al 2 O 3 system and are listed in Table 3. Some studies 51,52 indicated that temperature might affect melt structure, but previous experiment showed that the structures of CaO−SiO 2 −Al 2 O 3 −Fe x O slags changed only slightly with the temperature over a range of 1673−1873 K. Hence, the influence of temperature on the oxygen bond database can be ignored. All the oxygen bond values corresponding to the slag with a specific composition in any temperature of 1673−1873 K can be obtained from the database.…”