The Effect of Calcium Fluoride on Slag Viscosity
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t steelmaking processes, it is of considerable importance to keep the slag viscosity low to ensure fast heat and mass transfer. Low viscosity is also often one of the foremost factors when choosing slag for secondary steelmaking. One of the most common measures to lower the slag viscosity and its melting temperature is to add a certain amount of calcium fluoride to the slag. In line with this direction, the effect CaF2 on slag viscosity has been studied over the years. One example is the investigation of the ternary system FeO-SiO2-CaF2 and quaternary system CaO-FeO-SiO2-CaF2 by Shahbazian,[1,2] who reported that the effect of CaF2 addition on the viscosities of ‘‘FeO’’-SiO2 slags is not as significant as in the case of CaO-SiO2 slags. Another example is the work by Behera and Mohanty,[3] who studied the viscosity of Al2O3-Cr2O3-CaO-CaF2 slags. Some researchers have also investigated the mechanisms of the effects of calcium fluoride on slag viscosity.[4–9] In addition, several models have been proposed to estimate viscosity of slags containing calcium fluoride.[10–13] However, the viscosity data for multicomponent slags containing calcium fluoride are still scarce, especially for high-basicity slags used in secondary steelmaking. In this context, the current work aims to investigate the effects of CaF2 on the viscosity of high-basicity Al2O3-CaO-MgO-SiO2 (-CaF2) slags at steelmaking temperatures. The experimental setup is shown schematically in Figure 1. A Brookfield digital viscometer (model: LIUSHUN WU, Graduate Student, JIMMY GRAN, Researcher, and DU SICHEN, Professor, are with the Department of Materials Science and Engineering, Royal Institute of Technology, 10044 Stockholm, Sweden. Contact e-mail: [email protected] Manuscript submitted May 6, 2011. Article published online July 6, 2011. 928—VOLUME 42B, OCTOBER 2011
DV-II+ Pro; Brookfield Engineering Laboratories, Inc., Middleboro, MA) was used. The viscometer was placed in a vacuum tight poly(methyl methacrylate) (PMMA) box on the top of the furnace. The viscosity could be followed by a personal computer (PC) as a function of time using the software supplied by Brookfield. A graphite resistance furnace was used for this investigation. The variation of the temperature in the even temperature zone of the furnace was less than ± 3 K. The furnace could be moved along the vertical direction by a hydraulic moving system. The temperature of sample was measured by Pt-6 pct Rh/Pt-30 pct Rh thermocouple in a molybdenum rod connected to the molybdenum platform. The thermocouple was kept in an alumina tube with closed upper end. Molybdenum crucible (inner diameter: 42 mm, and inner height: 153 mm) was used for all the measurements. The crucible was placed on the molybdenum platform. The spindle was also made of Mo. The setup allowed fast quenching of the sample along with crucible by moving them rapidly into the quenching chamber. The spindle consisted of a bob and a shaft. The dimensions of the bob were 19 mm in diameter and 18 mm in height. The diameter of the shaft was 4 mm, and its l
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