The doctoral dissertations of the former Helsinki University of Technology (TKK) and Aalto University Schools of Technology (CHEM, ELEC, ENG, SCI) published in electronic format are available in the electronic publications archive of Aalto University - Aaltodoc.
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Experimental Study and Modelling of Viscosity of Chromium Containing Slags

Lasse Forsbacka

Dissertation for the degree of Doctor of Science in Technology to be presented with due permission of the Department of Materials Science and Engineering for public examination and debate in Auditorium V1 at Helsinki University of Technology (Espoo, Finland) on the 7th of December, 2007, at 12 o'clock noon.

Overview in PDF format (ISBN 978-951-22-9033-8)   [2183 KB]
Dissertation is also available in print (ISBN 978-951-22-9032-1)

Abstract

An apparatus was constructed to measure the viscosities of molten slags at high temperatures up to 1750 °C. Techniques and methods of viscosity measurement for chromium containing slags were developed using a concentric rotating cylinder method in combination with a high temperature furnace. The viscosities were measured for Al2O3-CaO-MgO-SiO2 slags, and for several slag systems containing chromium oxides, from a quasi-binary system CrOx-SiO2 to quasi-ternary and quaternary systems.

At low oxygen partial pressures such as in typical metallurgical processes, the chromium in the slag appears simultaneously as divalent (CrO) and trivalent (CrO1.5) oxides. It was proven that decreasing the oxygen partial pressure in the system by contacting the slag with metallic chromium increased the amount of divalent CrO, which consequently lowered the melting temperature and viscosity of the slag as well. The measured data were used to develop viscosity models based on the Iida model, the modified Iida model, the modified Urbain model and neural network algorithm methods. The Iida model and the modified Iida model performed well for slags with relatively low chromium content, less than 5 wt. %. In favour of the Iida model, it must be remembered that the chromium content in metallurgical slags is normally quite low. Also, the modified Urbain model accurately predicted the viscosities of slags with higher chromium levels. The neural network computation also proved to be a promising approach for predicting viscosities of metallurgical slags.

This thesis consists of an overview and of the following 5 publications:

  1. Forsbacka L., Holappa L., Iida T., Kita Y., Toda Y., Experimental study of viscosities of selected CaO-MgO-Al2O3-SiO2 slags and application of the Iida model, Scandinavian Journal of Metallurgy, Blackwell Publishing, 2003; 32: 273-280.
  2. Forsbacka L., Holappa L., Viscosity of CaO-CrOx-SiO2 slags in a relatively high oxygen partial pressure atmosphere, Scandinavian Journal of Metallurgy, 2004; 33: 261-268.
  3. Forsbacka L., Holappa L., Viscosity of SiO2-CaO-CrOx slags in contact with metallic chromium and application of the Iida model, Proceedings of the VII International Conference on Molten Slags, Fluxes and Salts, Capetown, South Africa, SAIMM, Johannesburg, 2004, 129-136.
  4. Forsbacka L., Holappa L., Kondratiev A., Jak E., Experimental study and modelling of viscosity of chromium containing slags, Steel Research International, 2007; 78, no. 9: 676-684.
  5. Nakamoto M., Forsbacka L., Holappa L., Assessment of viscosity of slags in ferrochromium process, Proceedings of the XI International Conference on Innovations in the Ferro Alloy Industry (INFACON XI), 2007; vol. 1: 159-164.

Keywords: slag viscosity, viscosity modelling, ferrochromium slag, chromium containing slag

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© 2007 Helsinki University of Technology

Last update 2011-05-26