Experimental studies of the viscosities in CaO-MnO-SiO 2 and CaO-Fe n O-MnO-SiO 2 slags
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furnace is controlled by a 818 controller supplied by Eurotherm using an optical pyrometer sensor. Pure iron crucibles and spindles were employed. The dimensions of crucibles and spindles used in the present work are listed in Table I. The viscometer was calibrated periodically at both ambient and experimental temperatures. While four standard mineral oils (Brookfield Viscosity Standard) with viscosities 9.85, 96, 485, and 1250 dPa⭈s, respectively, were used for the calibration at room temperature, a reference slag (15.5 mass pct Al2O3-21.2 mass pct Li2O-63.3 mass pct SiO2) developed by European Union[5] was employed for the high-temperature calibration. CaO, MgO, and SiO2 powders were calcined at 1273 K for more than 12 hours in a muffle furnace. The Fe2O3 and MnO powders were dried at 398 K overnight before use. The powders were mixed thoroughly and premelted in an iron crucible, which was also later used for the viscosity measurements. In a general run, the crucible with premelted slag was placed in the uniform temperature zone (⫾3 K) of the furnace. A Pt-10 pct Rh/Pt thermocouple was placed in contact with the base of the crucible to measure the sample temperature accurately. A stream of purified argon gas was passed through the reaction tube for 1 hour before the sample was heated up. Thereafter, a constant flow rate (about 0.2 L⭈min⫺1) of argon was maintained
F.-Z. JI, Research Associate, is with the Division of Metallurgy, Royal Institute of Technology, SE-100 44 Stockholm, Sweden. Manuscript submitted December 18, 1998. METALLURGICAL AND MATERIALS TRANSACTIONS B
throughout the entire experiment. The slag was heated to a required temperature at a heating rate of 5 K⭈min⫺1. When the thermal equilibrium was reached, the spindle rotating at 40 to 60 rpm was immersed into the molten slag by adjusting the length of TEFLON bellows. The tip of the spindle was kept 1.2 cm above the bottom of crucible, and the length of the shaft immersed in the slag was about 1 cm. Measurements were carried out using five different rotation speeds at each temperature. The measurement time at each rotating speed was 2 minutes. The measured viscosities of the CaO-MnO-SiO2 and CaOFenO-MnO-SiO2 slags are listed in Tables II and III, respectively. Six slag compositions were chosen in the CaO-MnOSiO2 system and viscosities of ten CaO-FenO-MnO-SiO2 slags were measured. The viscosities presented in Tables II and III are average values over five values obtained at different rotation speeds. The standard deviation of the experimental data from the average values was usually found to be less than 1 pct. The viscosities of the CaO-MnO-SiO2 slags have been studied by a number of research group.[6–12] In Figure 2, the present experimental results for the CaO-MnO-SiO2 system at 1753 K are compared with the viscosity values reported by Segers et al.[6] and Kawahara et al.[7] The present viscosities at 1753 K are found to be in agreement with the isoviscosity lines at 1773 K reported by both Segers et al. and Kawahara et al. On the other hand, the v
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