Influence of CaF 2 on the Viscosity and Structure of Manganese Ferroalloys Smelting Slags
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VISCOSITY of silicate melts at high temperatures has been widely investigated because of the close relationship between the macroscopic thermophysical properties of slags and their microscopic molecular structure, which strongly affects reaction efficiency in process metallurgy.[1–26] Recently, we thoroughly evaluated the novel structure–viscosity relationship of the MnO-CaO-SiO2 slag system using Raman spectroscopy due to the importance of this system in smelting and refining processes for the production of manganese ferroalloys.[21,22] Enhancement of slag-metal reaction kinetics is desirable to increase the production rate and decrease the cost of smelting and refining processes for Mn ferroalloys. Fluorspar (CaF2) addition may improve slag-metal reaction kinetics of MnO-containing slags at high temperatures by decreasing the viscosity of the slags, because CaF2 is well known to decrease the viscosity of silicate melts.[3–12,15,19,20,24,25] The effect of CaF2 on the viscosity of various silicate melts has been investigated experimentally by several researchers for CaO-SiO2
JOO HYUN PARK, Professor, and TAE SUNG KIM, Graduate Student, are with Department of Materials Engineering, Hanyang University, Ansan 426-791, Korea. Contact e-mail: basicity@hanyang. ac.kr KYU YEOL KO, formerly Graduate Student, is with Metals and Materials Research Department, LS-Nikko Copper, Ulsan 70, Korea. Manuscript submitted September 25, 2014. METALLURGICAL AND MATERIALS TRANSACTIONS B
(-MgO, -MnO)-CaF2, [3–5,10–12,24,25] FeO(-CaO)-SiO2CaF2,[6–8] CaO-SiO2-Na2O-Li2O-CaF2, [19] and CaOAl2O3-SiO2-MgO-CaF2 systems.[20] The above studies showed that viscosity itself and the activation energy of Newtonian flow of silicate melts generally decreased with increasing CaF2 content due to depolymerization reactions of silicate networks, indicating that the addition of CaF2 is more effective at higher silica concentrations. However, the effect of CaF2 on the viscosity of the FeO-SiO2 slags was not significant, in contrast to its effects on the CaO-SiO2 slags.[6] In MO (M = Mg, Na2)-containing slags, the addition of CaF2 had a limited effect on viscosity within a specific range of CaF2 concentration due to the contribution of basic oxides such as MgO and Na2O in addition to CaO to silicate depolymerization.[10–12,19] Furthermore, for highly basic slags with a silica content lower than about 10 mass pct, CaF2 suppressed the precipitation of solid phases at lower temperatures, whereas the effect of CaF2 on viscosity itself was less significant when the slags were completely liquid at high temperatures.[20,26] Little experimental work has been done to determine the effect of CaF2 on the viscosity of MnO-containing silicate melts,[25] even though there is some experimental data regarding the viscosity of the CaO-MnO-SiO2 ternary slags.[1,2,7] Therefore, in the current study, we measured the viscosity of the CaO-SiO2-MnO-CaF2 slags with the composition of CaO/SiO2 = 0.5 (mass pct ratio) to clarify the effect of CaF2 on the viscous flow of molten slags at high temperatur
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