Electronically driven transport of oxygen from liquid iron to CO + CO 2 gas mixtures through stabilized zirconia
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o
(liquid iron)
I (in ZrO2-CaO ) / (CO + CO2)
An alumina crucible was charged with liquid iron containing 580 _+ 10 ppm oxygen. A calcia-stabilized zirconia tube (closed at one end) was immersed in the liquid iron. The inside of the zirconia tube was flushed with a stream of CO + CO 2 gas mixture. Oxygen was removed from liquid iron to the CO + CO 2 gas mixture without application of an external current. Kinetics of oxygen transport in this system are discussed in terms of mixed ionic and electronic conduction of the zirconia, and also diffusion of oxygen in liquid iron. The rate controlling step for this oxygen removal process was found to be transport of oxygen across a boundary layer in the melt at the melt/electrolyte interface. S I N C E the pioneering work of Kiukkola and Wagner t on solid-oxide electrolytes, stabilized zirconia has received attention with regard to its application in both thermodynamic and kinetic studies of high-temperature metallurgical systems. Equilibrium studies involving such electrolytes are based on the open-circuit measurement of emf iff electrochemical cells, which is related to the chemical potential gradient of oxygen. The principle of kinetic studies is the application of dc voltages across electrochemical oxygen cells. Faraday's law gives the interrelation between current and the rate of oxygen transport through the electrolyte. These two types of application of solid electrolytes have recently become important especially in physicochemical studies of iron and steelmaking. In steelmaking processes, low oxygen contents are often essential with regard to both ingot and continuously cast steel. The key to better control of deoxidation of liquid steel is a sensing device to measure rapidly the concentration of oxygen in liquid steel. Electrochemical oxygen probes involving a solidoxide electrolyte are useful for this purpose. The electrolyte utilized in these probes is sintered zirconia stabilized by either MgO, CaO or YzO3. This method offers the advantage of being simple to operate, hence requiring a minimum amount of operators' time and skill. However, because o f n-type electronic conduction in stabilized zirconia, the performance of an electrochemical cell at steelmaking temperatures is often handicapped, z,3 Electrochemical deoxidation of liquid iron is another
M. IWASE, on leave from the Department of Metallurgy, Kyoto University, Kyoto, Japan, and A. MCLEAN, Professor, are with the Department of Metallurgy and Materials Science, University of Toronto, Toronto, Canada. M. TANIDA, formerly Graduate Student at Kyoto University, is now with Hirohata Steel Plant, Nippon Steel Corp. T. MORI is Professor of Metallurgy, Kyoto University, Kyoto, Japan. Manuscript submitted October 29, 1980. METALLURGICAL TRANSACTIONS B
example of the application of solid-oxide electrolytes in steelmaking. 4 Chemical deoxidation leads to nonmetallic reaction products which can cause, for example, problems during continuous casting due to interaction with nozzles. An electrochemical deoxidation t
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