Effect of CaF2 on the Viscosity and Microstructure of CaO–SiO2–Al2O3 Based Continuous Casting Mold Flux

Abstract

In this study, a CaO–SiO2–Al2O3-based continuous casting mold flux was designed using the FactSage thermodynamics software to determine the composition range of CaF2. The viscosity characteristics of the mold flux were determined using a rotating viscometer. The results show that the constant temperature viscosity at 1300 °C decreases gradually as CaF2 content is increased from 3% to 11% in the CaO–SiO2–Al2O3-based slag. Viscosity is reduced from 0.854 to 0.241 Pa·s, viscous the flow activation energy is reduced from 157.74 to 114.34 kJ·mol−1, and the break temperature is reduced from 1280 to 1180 °C. Furthermore, when the CaF2 content is increased from 3% to 11%, the number of nonbridging fluorine bonds (Al–F structure and Si–F structure) in the melt increases to 287, the number of bridging fluorine bonds (Al–F–Al structure, Si–F–Si structure, and Si–F–Si structure) is only 17, and the network rupture of fluorine ions in the system is larger than the network formation. Consequently, both the degree of polymerization and viscosity are reduced.

Effect of CaF₂ on Viscosity and Refining Ability of Highly Basic Slags for Duplex Stainless Steel

“…Such a phenomenon is consistent with previous studies. [16][17][18][19][20][21][22][23][24][25][26] Physical properties of slags including viscosity intrinsically depend on ionic structure of molten slags. Therefore, to clarify the mechanism of fluorine (F) ions in decreasing slag viscosity, various spectroscopic instruments, such as nuclear magnetic resonance (NMR) spectroscopy, 42) Raman spectroscopy, 25,30) X-ray photoelectron spectroscopy (XPS) 22,43) and Fourier transform infrared (FTIR) spectroscopy, 44,45) as well as molecular dynamics simulation method [45][46][47] have been used to explore the effect of F ions on the structural changes of molten slags.…”

“…Deng et al 20) revealed that CaF 2 addition not only decreases the viscosity of low basicity SiO 2 -CaO-Al 2 O 3 -MgO silicate melts also changes the crystallization behavior from spherical diopside to plate-like anorthite. Wang et al 21) observed that the viscosity of CaO-SiO 2 -Al 2 O 3 -based low basicity mold fluxes decreases continuously with increasing CaF 2 content from 3% to 11%. Similar results were also obtained for low basicity mold fluxes by other researchers.…”

The Microstructure Formation in Slag Solidification at Continuous Casting Mold

“…The remaining liquid becomes poor in Ca and F and richer in Na and Al as the cuspidine continues to grow in block-shaped morphology. The reduction of either F or CaF 2 results in a drastic increase in the viscosity of the remaining liquid [24]. Moreover, the increase of Al 2 O 3 also causes the significant surge in viscosity [25].…”

Viskositas: Viscosity Prediction of Multicomponent Chemical Systems

“…Fluorite (CaF2) is also considered a chemical species that decreases the viscosity of chemical systems. Two mechanisms of fluorite in silicates are described in Equations 19-20 [70][71][72]. There is a break in the structure by the action of fluorite, thus decreasing the viscosity of the chemical system.…”

“…There is a break in the structure by the action of fluorite, thus decreasing the viscosity of the chemical system. Fluorite decreases the viscosity of the chemical systems SiO2-Al2O3-MgO-MnO2-Fe2O3-Na2O-CaO-K2O-CaF2, CaO-SiO2-Al2O3-CaF2 [70], CaO-SiO2-MgO-CaF2 [71], CaO-SiO2-Na2O-Al2O3-MgO-CaF2-FeO-Li2O-B2O3 [72], CaO-SiO2, CaO-Al2O3-based mold flux [69] and in fluxes [59].…”