MgO Solubility in Steelmaking Slags
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Slags are used to control high-temperature metallurgical processes and based on their chemistry can cause MgO to dissolve from refractory brick into the slag. MgO solubility is affected by slag’s FeO, and Al2O3 contents, as well as basicity (CaO/SiO2), and temperature. In steelmaking process, a predominantly liquid, MgO-saturated slag is usually preferred. Long furnace-lining live is achieved by saturating the slag with MgO. Additionally, liquid slag promotes the mass
MOHAMMED A. TAYEB, Research Engineer and Ph.D. Student, is with the SABIC Technology & Innovation, Jubail Industrial City, Saudi Arabia and also with Carnegie Mellon University, Pittsburgh, PA. Contact e-mail: [email protected]; [email protected] ANDRE N. ASSIS, formerly Ph.D. Candidate with Carnegie Mellon University, is now with the Vallourec Star, Youngstown, OH. SEETHARAMAN SRIDHAR, formerly Professor with Carnegie Mellon University, is now with the University of Warwick, Coventry, U.K. RICHARD J. FRUEHAN, Professor, is with Carnegie Mellon University. Manuscript submitted February 23, 2015. METALLURGICAL AND MATERIALS TRANSACTIONS B
transfer process, where undesirable elements such as phosphorus will partition into the slag phase.[1] The authors have studied dephosphorization in steelmaking by running laboratory measurements using MgO crucibles. The experimental procedures are given elsewhere[2,3] in detail. Briefly, 12 to 18 g of Fe alloy containing about 0.1 wt pct P and 6 to 8 g of a slag were equilibrated in a high purity MgO crucible (2.54 cm outer diameter 9 3.157 cm height). The metal analysis for phosphorus was carried out by inductively coupled plasma-mass spectrometry (ICP-MS) with a reported limit of 20 ppm for phosphorus where most of the current experiments exceeded that level. The slag phase was analyzed by X-ray fluorescence (XRF). Table I shows the slag compositions of current experiments. High alumina slags (up to 14 wt pct) in current experiments was analyzed by SEM/EDS and no magnesium aluminate spinel (MgAl2O4) formation was observed. This result was as well confirmed by FactSage calculations. The equilibration time was set for up to 10 hours at 1873 K (1600 C). The MgO content was constant after 4 hours of equilibration indicating equilibrium with respect to MgO was achieved. During the experiments, dissolution of MgO from the crucible was noticed. Thus, there was a consistent increase of MgO content (MgO pick up) in most of the slag samples through the course of the experiments. The software thermodynamic package ‘‘FactSage’’ was used to determine the initial ‘‘fully liquid’’ slag composition and the MgO saturation content. However, as mentioned earlier, the majority of the analyzed slags showed a higher final MgO content. The MgO pickup ranged from
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