Studies of Vaporization of Chromium from Thin Slag Films at Steelmaking Temperatures in Oxidizing Atmosphere
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CHROMIUM is an important alloying element in stainless steel. During the production of stainless steel, the final slag after oxygen blowing has a chromium oxide content as high as 8 mass pct as is known in Swedish steelmaking practice.[1] In view of the carcinogenic effect of hexavalent chromium, efforts are made world-wide to stabilize chromium in the silicate matrix of the solidified slag before disposal with a view to avoid the leaching of the harmful oxide by acid rains over a time period. On the other hand, very little information is found in literature regarding the emission of CrO3 vapor from slags during tapping of the slag after making alloy steel grades containing chromium. The present work was aimed at examining the possibility of CrO3 emissions from Cr-containing slags at steelmaking temperatures and the extent of the same to evaluate the health hazard aspects on the shop floor. A thin film sample was used from which, the loss of Cr was followed in the temperature range 1673 K to 1873 K (1400 °C to 1600 °C). WDS analysis was used in the post-experiment samples to get the average Cr content of the slag films. The technique was originally developed at the Institute of Iron and Steel Technology, Technical University Bergakademie Freiberg (TUBAF), Germany by two of the present authors along with other coworkers[2] to study the vaporization of V2O5 from slags
SESHADRI SEETHARAMAN, formerly Mercator Visiting Professor with the Institute of Iron and Steel Technology, TU-Bergakademie, 09596 Freiberg Germany, is now Professor Emeritus with the Division of Materials Process Science, Royal Institute of Technology (KTH), SE-100 44 Stockholm, Sweden. GALINA JELKINA ALBERTSSON, Ph.D. Student, is with the Division of Materials Process Science, Royal Institute of Technology (KTH). Contact e-mail: [email protected] PIOTR SCHELLER, Professor Dr.-Ing. habil., is with the TU Bergakdemie Freiberg, 09596 Freiberg, Germany. Manuscript submitted December 31, 2012. METALLURGICAL AND MATERIALS TRANSACTIONS B
containing vanadium. The present studies were carried out with respect to the gaseous emission of CrO3 from chromium-containing slags under three different oxygen partial pressures, oxygen, air, and argon. A. Thermodynamic Analysis Chromium exhibits three stable valence states in slags, viz. Cr2+, Cr3+, and Cr6+ and the corresponding oxides species are CrO, Cr2O3, and CrO3. In the case of Cr-containing slags, Wang et al.[3] have shown that, at low oxygen partial pressures, Cr exists in two valence states, viz. Cr2+ and Cr3+. The latter was reported to be stable at higher basicities and higher oxygen partial pressures. Morita et al.,[4] in their studies on the solubility of MgO-Cr2O3 in CaO-MgO-Al2O3-SiO2 slags reported that, in MgO-CaO melts containing as much as 40 to 55 wt pct CrOx, more than 50 pct of chromium exists as Cr6+ in the high CaO and low MgO region. In a subsequent work, Morita et al.[5] had shown that, in the case of MgO-CrOx-SiO2 melts, at 1873 K (1600 °C), the activity coefficient of chromium oxide (cCrO1.5) s
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