The effect of CaF 2 on the viscosities and structures of CaO-SiO 2 (-MgO)-CaF 2 slags
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FLUORSPAR is used in primary and secondary steelmaking processes to improve the fluidity of molten slags. The mold fluxes used in continuous casting also contain about 10 to 20 mass pct fluorides. However, the consumption of CaF2 in the steelmaking industry has been restricted due to its harmful effect on human health, the environment, and operation equipment. The effect of CaF2 on the viscosity of silicate melts has recently been investigated by some researchers. Shahbazian et al. concluded that the CaF2 decreased the viscosity of the CaO-SiO2-CaF2 ((mass pct CaO)/(mass pct SiO2), B ⬵ 0.6 to 0.9, 13 to 41 mass pct CaF2) system.[1] Tribe et al. suggested that the solidification temperature of the basic systems (B ⬵ 1.3 to 2.5) would be higher than that of the acidic compositions (B ⬵ 0.5 to 0.8) in the CaO-SiO2MgO-CaF2 slags.[2] However, the content of CaF2 in these studies would be significantly high; thus, the effect of CaF2 on the viscosity, structure, and the solidification behavior of slags with CaF2 contents less than about 15 mass pct has not yet been clarified. Therefore, in the present study, the viscosity of the CaOSiO2(-MgO)-(ⱕ15 mass pct) CaF2 slags has been measured to clarify the effect of CaF2 on the viscous flow of molten slags at high temperatures and the solidification behavior of slags. In addition, the infrared (IR) spectra of the quenched slags were analyzed to understand the structural JOO HYUN PARK, Researcher, formerly Doctoral Student, Department of Metallurgical Engineering, Yonsei University, is with the STS Research Group, Technical Research Laboratory, POSCO, Pohang 790-785, Korea. Contact e-mail: [email protected] DONG JOON MIN, POSCO Professor and Assistant Dean of Engineering College, is with the Department of Metallurgical Engineering, Yonsei University, Seoul 120-749, Korea. HYO SEOK SONG, Senior Researcher, is with the STS Research Group, Technical Research Laboratory, POSCO. Manuscript submitted January 22, 2002. METALLURGICAL AND MATERIALS TRANSACTIONS B
role of CaF2 in the depolymerization of silicate network in a microscopic view. II. EXPERIMENTAL A. Sample Preparation for Viscosity Measurement All of the slag samples were prepared using reagentgrade chemicals. The master slags were used for the premelting of slags, and then, each component was added into the premelted slags to control the exact composition in each run. The premelting was carried out by using a graphite crucible under an Ar atmosphere in a super kanthal electric furnace. B. Experimental Procedure The rotating cylinder method was used in the present study and a schematic diagram of the experimental apparatus is shown in Figure 1. A rotating viscometer (Brookfield, model RVDV-II⫹, Middleboro, MA) set on the super kanthal electric furnace was connected with a computer to record the value of the torque from the rotation of spindle. The temperature was measured using an R-type (Pt/Pt-13 pct Rh) thermocouple in an alumina sheath placed in contact with the base of the crucible. The experimental temperature ran
