Kinetics of carbide formation from reduced iron in CO-H 2 -H 2 S mixtures
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rial for manufacturing iron carbide from iron ore as an alternative iron source was made only a few decades ago,[1] and the operation of the first commercial plant for iron-carbide production began in Trinidad by Nucor in 1994.[2] Since then, fundamental studies[3–11] for producing iron carbides from iron ore have been actively conducted. Since iron carbides are metastable phases, however, ironcarbide production is always accompanied by their decomposition and carbon decomposition. So far, no reliable kinetic study has been reported on iron-carbide formation. Recently, iron carbides of and phases were successfully produced as almost single phases by the present authors[4,5,7,9–11] by suppressing the iron carbide’s decomposition and the carbon deposition by adding a small amount of H2S to CO-H2 mixtures. In our previous studies,[4,7,9–11] the following conclusions were obtained: (a) the best temperature range is from 823 to 1123 K, and (b) the best sulfur activity range is the range 0.1 to 0.5 relative to the Fe/FeS equilibrium. Under these conditions, reduced iron can be completely converted to iron carbides without any formation of FeS. With the iron-carbide formation reactions furthermore, it was experimentally confirmed that pressuring enhances the carbide formation not only kinetically but also thermodynamically. In this study, the kinetics of carbide formation from iron YOSHIAKI IGUCHI, Professor, is with the Nagoya Institute of Technology, Nagoya 466-8555, Japan. SATOSHI SAWAI, formerly Graduate Student, Graduate School, Nagoya Institute of Technology, is with Toyota Communication Systems, Inc., Nagoya, Japan. KATSUNORI OHIWA, formerly Graduate Student, Graduate School, Nagoya Institute of Technology, is with Fujitsu Chubu Systems, Inc., Nagoya, Japan. This article is based on a presentation made in the “Geoffrey Belton Memorial Symposium,” held in January 2000, in Sydney, Australia, under the joint sponsorship of ISS and TMS. METALLURGICAL AND MATERIALS TRANSACTIONS B
ore completely reduced in an H2-H2S mixture were established on the basis of highly accurate kinetic measurements in CO-H2-H2S mixtures by gravimetric technique. The iron-carbide formation experiments were conducted in CO-H2-H2S and CO-COS mixtures of a sulfur activity range less than unity under the total pressures up to 0.1 MPa (1 atm). On the basis of the experimental results, the reaction mechanism of the carbide formation from reduced iron in CO-H2-H2S mixtures was discussed, and the kinetic equation for the iron-carbide formation was derived. II. EXPERIMENTAL Weight gain by carbide formation from reduced iron was measured by a high sensitivity thermobalance (Shimadzu, Kyoto, Japan MTG-40) with the accuracy of ⫾ 1 g. The iron-carbide formation rate could be measured thermogravimetrically only by completely depressing the carbon deposition with the addition of sulfur to the reaction gas mixtures. Particles of a hematite ore, whose composition is shown in Table I, were used in the present experiments. The size range was 0.15 to 0.21 mm.
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