Study on Apparent Viscosity and Structure of Foaming Slag
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foaming has been studied for decades due to its important role in both the Linz–Donawitz converter (LD-converter) and the electric arc furnace.[1–6] Slag foaming is a very complicated phenomenon involving a number of phases, possibly (1) gas phases, (2) liquid phase(s), and even (3) solid phases.[2,7,8] The complexity of foaming slag is one of the foremost hindrances for the researchers to understand the mechanism of slag–metal reactions in the LD-converter. Whether the reactions in the processes take place mostly between the steel droplets and the foaming slag or at the interface between the slag and steel bath has for long been an interesting topic.[9] A better understanding of the foaming slag will help clarify this issue, which is essential for any sound dynamic process model. Very interesting behaviors have recently been noticed in the foam generated by passing argon gas through silicone oil.[10] The foamed silicone oil shows shear-thinning non-Newtonian behavior; and the apparent viscosities measured show values of 2 to 5 times higher than the dynamic viscosity of the silicone oil. As a continuation, the present work studies the behavior of slag foams at elevated temperature. The focus is twofold, namely (1)
JOHAN MARTINSSON, Graduate Student, BJO¨RN GLASER, Assistant Professor, and DU SICHEN, Professor, are with the Department of Materials Science and Engineering, Royal Institute of Technology, 10044 Stockholm, Sweden. Contact e-mail: sichen@ kth.se Manuscript submitted February 10, 2016. Article published online July 26, 2016. 2710—VOLUME 47B, OCTOBER 2016
the structure of the slag foam, whether it is similar to the foam of silicone oil and (2) the apparent viscosity of the slag foam. The foam is generated by letting the slag react with hot metal and graphite powder to form CO and CO2. The slag composition was chosen based on the LD-converter slag, namely CaO(43mass pct)-SiO2(32mass pct)-FeO(25mass pct). The FeO was produced first by mixing Fe2O3 and pure iron powder and then sintering the mixture at 1123 K (850 °C) for approximately 70 hours in a closed iron crucible in argon atmosphere. The sintered FeO was then crushed into small pieces. A premelted CaO(54 mass pct)-SiO2(46 mass pct) slag was used as the master slag. The slag was adjusted to the target composition by addition of FeO and calcined CaO. The experimental setup is schematically shown in Figure 1. An induction furnace with a water-cooled copper coil was employed to heat the sample to the experimental temperature, viz. 1873 K (1600 °C), and the sample temperature was maintained throughout the measurement. Since thermocouples would be affected by the magnetic field induced by the furnace,[11] an infrared temperature sensor (model thermoMETER CTM-1SF75-C3) was used for temperature measurement. The sensor was calibrated with a pyrometer of model Raytek Thermoalert ET before use. Because the variation in magnetic fields changes the temperature in short distances, the temperature could therefore be somewhat different in the middle part of the sample whe
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