Some Thermodynamic Aspects of the Oxides of Chromium
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Chromium is an important alloying element in stainless steelmaking. During the production of chromiumcontaining steels, the resultant slag can contain as much
AYUSH MITTAL, Bachelor of Technology (B.Tech) Student, is with the Department of Metallurgical and Materials Engineering, Indian Institute of Technology, Roorkee 247 667, India, and also with the Department of Materials Engineering, Indian Institute of Science, Bangalore 560 012, India. GALINA JELKINA ALBERTSSON, formerly PhD Student and is now Doctor of Philosophy, with the Department of Materials Science and Engineering, Royal Institute of Technology, 100 44 Stockholm, Sweden. Contact e-mail: galinaa@ kth.se GOVIND SHARAN GUPTA, Professor, is with Department of Materials Engineering, Indian Institute of Science. SESHADRI SEETHARAMAN, formerly Visiting Professor with the Department of Materials Engineering, Indian Institute of Science, and is now Professor Emeritus with the Department of Materials Science and Engineering, Royal Institute of Technology. SANKARAN SUBRAMANIAN, Professor, is with the Department of Materials Engineering, Indian Institute of Science. Manuscript submitted July 15, 2013. METALLURGICAL AND MATERIALS TRANSACTIONS B
as 8 mass pct Cr. As a result of the extremely carcinogenic nature of hexavalent chromium, serious efforts are made so that chromium is stabilized in the slag and does not get leached out by acid rains. On the other hand, little is known regarding the emission of the oxide of chromium during the tapping of the slag at steelmaking temperatures. A recent publication[1] has pointed out the risk of Cr-emission from slags at high temperatures under high oxygen potentials. Such emissions may also occur if chromite refractories are exposed to air at high temperatures. While the emission of Cr as a gaseous oxide could be confirmed in this work,[1] the nature of the oxide phase emitted as to whether it was hexavalent chromium is not clear. Because of the importance of the system Cr–O in stainless steel processing as well as of Cr-emissions at high temperatures, the present work was taken up to examine the stabilities of various oxides of chromium. Current work presents the data corresponding to the thermodynamic properties of the oxides of chromium, with emphasis on the emission of hexavalent chromium from slags. Critical analysis of the experimental data available with emphasis on self-consistency, third law analysis, where it is possible and comparisons have been carried out. The current article addresses an important question; viz. which oxide is emitted when chromium slags are heated in an oxidizing atmosphere at steelmaking temperatures. The alloy steel industries in Sweden have already expressed concern with respect to the emission of Cr6+. Some of the present authors have carried out experimental investigations with respect to the thermodynamics of chromium-containing slags.[1–6] Among these, the publication on the studies on the vaporization of chromium from thin slag films at steelmaking temperatures in oxidizing atmosphere[1]
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