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Electrochemical deoxidation of molten steel with application of an oxygen permeable membrane

Title
Electrochemical deoxidation of molten steel with application of an oxygen permeable membrane
Authors
Koo, HWPark, HJChoi, GMLee, HG
POSTECH Authors
Choi, GM
Date Issued
2007-01
Publisher
IRON STEEL INST JAPAN KEIDANREN KAIKA
Abstract
The deoxidation of molten steel has been studied by employing an electrochemical cell which utilizes a solid-oxide electrolyte. This technique enables deoxidation of liquid steels without leaving deoxidation products in the steel. Y2O3-stabilized ZrO2 (YSZ) is used as an oxygen-permeable membrane due to its reasonably high mixed-ionic and electronic conductivity and thermal stability at elevated temperature in low oxygen partial pressure (P-O2). In order to investigate the rate-determining steps involved in this electrochemical deoxidation process, the oxygen-permeation experiment using a YSZ disk is performed to measure the oxygen flux as a function of P-O2, and temperature. The measured oxygen flux is about one order of magnitude smaller than the estimated value from Wagner equation that describes permeation under bulk-diffusion limit. Thus, oxygen permeation is mostly controlled by surface-exchange kinetics even at high temperature (similar to 1 600 degrees C) in reducing atmosphere. In the experiment of deoxidation of molten steel using a YSZ tube, the deoxidation rate is largely dependent on the surface-exchange kinetics as well. The deoxidation rate is much smaller than that calculated under the assumption of bulk-diffusion limit. Based on these results, the surface modification of YSZ is investigated as a way to enhance the deoxidation kinetics. Both surfaces of the membrane are coated with porous YSZ (Zr0.84Y0.16O2-delta), GDC (Ce0.8Gd0.2O2-delta) and LSC (La0.7Sr0.3CrO3-delta) during oxygen permeation experiment in the gas phase. During the deoxidation experiment in the steel melt, only the permeate side is coated with Pt, Mo-YSZ cermet and LSC. The oxygen permeation rate of YSZ drastically increased with coating. The increase also depended on the coating materials. Thus, it is shown that the oxygen permeation through the membrane is mostly controlled by the surface-exchange kinetics. Similar trend can be seen in the deoxidation experiment, confirming the surface-exchange kinetics limit.
Keywords
deoxidation; electrochemical cell; solid-oxide electrolyte; oxygen-permeation; surface-exchange kinetics; surface modification; oxygen permeable membrane; deoxidation experiment; rate determining step; SOLID OXIDE ELECTROLYTE; STABILIZED ZIRCONIA; ELECTRICAL-PROPERTIES; GALVANIC DEOXIDATION; POROUS-ELECTRODES; COPPER MELTS; TRANSPORT; PERMEATION; METALS; SEMIPERMEABILITY
URI
https://oasis.postech.ac.kr/handle/2014.oak/29521
ISSN
0915-1559
Article Type
Article
Citation
ISIJ INTERNATIONAL, vol. 47, no. 5, page. 689 - 698, 2007-01
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최경만CHOI, GYEONG MAN
Dept of Materials Science & Enginrg
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