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Thermodynamic Studies of the Fe-Pt System and “Feo”-Containing Slags for Application Towards Ladle Refining

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Thermodynamic Studies of the Fe-Pt System and “Feo”-Containing Slags for Application Towards Ladle Refining Thermodynamic Studies of the Fe-Pt System and “FeO”-Containing Slags for Application Towards Ladle Refining Patrik Fredriksson Doctoral Dissertation Stockholm 2003 Royal Institute of Technology Department of Material Science and Engineering Division of Metallurgy Akademisk avhandling som med tillstånd av Kungliga Tekniska Högskolan i Stockholm, framlägges för offentlig granskning för avläggande av Teknologie doktorsexamen, fredagen den 7 November 2003, kl. 10.00 i Kollegiesalen, Administrationsbyggnaden, Kungliga Tekniska Högskolan, Valhallavägen 79 Stockholm ISRN KTH/MSE--03/36--SE+THMETU/AVH ISBN 91-7283-592-3 To Anna ii Abstract In the present work, the thermodynamic activites of iron oxide, denoted as “FeO” in the slag systems Al2O3-“FeO”, CaO-“FeO”, “FeO”-SiO2, Al2O3-“FeO”-SiO2, CaO- “FeO”-SiO2 and “FeO”-MgO-SiO2 were investigated by employing the gas equilibration technique at steelmaking temperatures. The strategy was to expose the molten slag mixtures kept in platinum crucibles for an oxygen potential, determined by a CO/CO2-ratio. A part of the iron reduced from the “FeO” in the slag phase was dissolved into the Pt crucible. In order to obtain the activites of “FeO”, chemical analysis of the quenched slag samples together with thermodynamic information of the binary metallic system Fe-Pt is required. Careful experimental work was carried out by employing a solid-state galvanic cell technique as well as calorimetric measurements in the temperature ranges of 1073-1273 K and 300-1988 K respectively. The outcome of these experiments was incorporated along with previous studies into a CALPHAD-type of thermodynamic assessment performed with the Thermo-Calc™ software. The proposed equilibrium diagram enabled extrapolation to higher temperatures. The experimentally obtained activites of “FeO” in the present work, along with earlier investigations were assessed with the KTH slag model, THERMOSLAG©. New binary parameters were evolved and incorporated in THERMOSLAG©. The present model calculations are compared with other commercially available software such as F*A*C*T™ and Thermo-Calc™. The validity of the modified model was investigated by measurements carried out in case of Al2O3-“FeO”-SiO2, CaO-“FeO”-SiO2 and “FeO”-MgO-SiO2 ternary slags. The potential of the model to compute the activities in the case of multicomponent slags was demonstrated. A correlation between the activity of a metallic oxide in a ternary slag system and the sulphide capacity of the slag was investigated by using the solubility of sulphur in the binary systems CaO-SiO2 and Al2O3-CaO along with the sulphide capacity of the Al2O3-CaO-SiO2 system. The estimated values of the activities were found to be in good agreement with the measured values. This correlation also gives the possibility to elucidate the applicability of Henry’s law to the activity of a metallic sulphide and to determine the order in the affinity of a cation to sulphur between two metallic oxides in a slag. Model calculations were performed with THERMOSLAG©, by using plant data from the ladle refining process at OVAKO Steel, Hofors, Sweden. It was found that oxygen estimations in the metal from the “FeO” analyses of slags, obtained by conventional sampling and analysis method were less reliable. Reliable estimation of the oxygen levels utilising the sulphur partition between the slag and the metal were carried out using THERMOSLAG® software. Keywords: Thermodynamics, Activity, Galvanic cell, Calorimetry, Gas equilibration technique, Iron-platinum alloys, FeO, Slags, Modelling, Ladle iii Acknowledgments There is one man that urged me on by way of his untiring support and seemingly unlimited belief in me, to that man, all else pales. This man, to whom I would like to express my sincere gratitude and appreciation, is Professor Seshadri Seetharaman. The author is grateful to Professor Du Sichen and Dr. Ragnhild E. Aune for valuable suggestions and fruitful discussions. Professor Bo Sundman, and Tech. Lic. Rosa Jerlerud, Division of Computational Thermodynamics, the Royal Institute of Technology, Stockholm, Sweden, and Dr. Alexandra Kusoffsky, the Swedish Institute of Metal Research, Stockholm, Sweden are gratefully acknowledged for their support and guidance into the world of modelling. Appreciation also goes to the CALPHAD:ians for giving an experimentalist access to your hemisphere. Dr. Johan Björkvall, MEFOS, Luleå, Sweden is gratefully acknowledged for interesting discussions, valuable comments and his helpfulness in high temperature thermochemistry issues, and other not so life-dependent matters. The author also wants to thank all of the colleagues at the division of Metallurgy for the support and encouragement during the years. A special thanks to my dear friends and colleagues, Dr. Anders Tilliander, Dr. Robert Eriksson and, Tech. Lic. Kristina Beskow respectively, for your friendship and listening abilities during these years in our grotto. Financial support for this work from The Swedish Board for Industrial and Technical Development (former NUTEK) and The Gerhard von Hofstens Foundation for Metallurgy and Research (Stiftelse för Metallurgi och Forskning) is gratefully acknowledged. Travelling grants from the Swedish Steel Producers´ Association and the Foundation for Applied Thermodynamics are gratefully acknowledged. The author would also like to express his appreciation to Mr. Peter Kling, the department technician, for his superb service, clever solutions and king-size green products. Stockholm, October 2003 Patrik Fredriksson iv Supplements The present thesis is based on the following papers: 1. On the Standard Gibbs Energy of Formation of CoO, P. Fredriksson and S. Seetharaman, ISRN KTH/MSE--03/31--SE+THMETU/ART, Accepted for publication in Scand. J. Metall. 2. Thermodynamic Studies of some Fe-Pt Alloys by the Solid Electrolyte Galvanic Cell Method, P. Fredriksson and S. Seetharaman, Scand. J. Metall., 30, 4, pp. 258-264, 2001. 3. Differential Thermal Analysis (DTA) of the Iron-Platinum System, P. Fredriksson, ISRN KTH/MSE--03/32--SE+THMETU/ART, Accepted for publication in Scand. J. Metall. 4. A Thermodynamic Assessment of the Fe-Pt System, P. Fredriksson and B. Sundman, CALPHAD, 25, 4, pp. 535-548, 2001. 5. Thermodynamic Activities of “FeO” in some Binary ”FeO”-Containing Slags, P. Fredriksson and S. Seetharaman, ISRN KTH/MSE--03/33--SE+THMETU/ART, Submitted to Steel Research International, September 2003. 6. Thermodynamic Activities of “FeO” in some Ternary “FeO”-Containing Slags, P. Fredriksson and S. Seetharaman, ISRN KTH/MSE--03/34--SE+THMETU/ART, Submitted to Steel Research International, October 2003. 7. Evaluation of Thermodynamic Activity of a Metallic Oxide in a Ternary Slag from the Sulphide Capacity of the Slag, M. Hayashi, N. Sano and P. Fredriksson, ISRN KTH/MSE--03/35--SE+THMETU/ART, Submitted to ISIJ International, October 2003. 8. Thermodynamic Studies of “FeO”-Containing Slags and their Impact on the Ladle Refining Process, P. Fredriksson and S. Seetharaman, ISRN KTH/MSE--03/37-- SE+THMETU/ART, Accepted for presentation at the 7:th International Conference on Molten Slags, Fluxes and Salts, Cape Town, South Africa, 25-28 January 2004. Parts of this work were presented in the following conferences: 1. Activity Measurements in Slag Systems by Gas Equilibration Technique, P. Fredriksson, M. M. Nzotta, R. E. Aune and S. Seetharaman, CALPHAD XXVIII, Grenoble, France, May 2-7, 1999. 2. Reactions Between Steel and Slag in the Ladle Process, P. Fredriksson, SCANMET, 1:st International Conference on Process Development in Iron and Steelmaking, Luleå, Sweden, June 7-8, 1999. v 3. Thermodynamic Investigation of the Fe-Pt System Coupled with some Gas Equilibration Measurements, P. Fredriksson and B. Sundman, Thermodynamics of Alloys, Stockholm, Sweden, May 8-11, 2000. 4. Activity Measurements in Slag Systems by Gas Equilibration Technique, P. Fredriksson and S. Seetharaman, 6:th International Conference on Molten Slags, Fluxes and Salts, Stockholm, Sweden-Helsinki, Finland, June 12-17, 2000. 5. A Thermodynamic Study of the Fe-Pt System, P. Fredriksson and B. Sundman, CALPHAD XXX, York, England, May 27-June 1, 2001. 6. Impact of Experimentation in Thermodynamic Studies of some Metallic and Oxidic Systems, R. E. Aune, P. Fredriksson and S. Seetharaman, Grafomed, Bor, IOC 2002: 34th International October Conference on Mining and Metallurgy Proceedings (Yugoslavia), pp. 570-575, 2002. 7. Experimentation and Modeling of FeO-Containing Slag Systems, P. Fredriksson and S. Seetharaman, Minerals, Metals and Materials Society (TMS), Proceedings of the EPD Congress 2003 held at the 2003 TMS Annual Meeting, March 2–6, San Diego (USA), pp. 83-97, 2003. Other contributions: 1. Solute Interactions with Dissolved Oxygen in Molten Copper Systems, R. E. Aune, P. Fredriksson and S. Seetharaman, Minerals, Metals and Materials Society (TMS), Yazawa International Symposium on Metallurgical and Materials Processing: Principles and Technologies; Vol. 1, Materials Processing Fundamentals and New Technologies (USA), pp. 119-130, 2003. 2. The Mysteries of Slags- Structure, Properties and Applications, M. Hayashi, R. E. Aune, P. Fredriksson and S. Seetharaman, Iron and Steel Society/AIME, ISSTech 2003 Conference Proceedings, Indianapolis, Indiana, (USA), pp. 309- 320, 2003. 3. Slags-Structure, Properties and Applications, M. Hayashi, R. E. Aune, P. Fredriksson, D. Sichen and S. Seetharaman, the International Symposium on Ionic Liquids in Honour of Professor Marcelle Gaune-Escard, Carry le Rouet,
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