Characterization of phases formed in the iron carbide process by X-ray diffraction, mossbauer, X-ray photoelectron spect
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I. INTRODUCTION
THE iron carbide process has been developed as an alternative ironmaking process, in which iron ore fines are reduced by hydrogen-methane gas mixture in a fluidized bed reactor at relatively low temperature.[1–8] The iron carbide process has some advantages over the conventional blast furnace (BF)-ironmaking, which includes a coke oven, sinter plant, and BF itself. Its main by-product is water vapor. Fine iron ore can be processed directly, thereby eliminating the agglomeration stage. The product, iron carbide, is nonpyrophoric, which makes it safe and easy to store and transport. It is an attractive feed material for electric arc furnace (EAF) steelmaking, as combustion of carbon decreases the electric energy consumption, makes EAF slag to foam, and decreases the content of dissolved nitrogen. However, the iron carbide process needs further development. Nucor Corporation recently announced the closure of the only commercial iron carbide plant in Trinidad because of numerous engineering and quality problems. This emphasizes the necessity of further research in fundamentals of iron carbide formation, which was undertaken in this project. Iron carbide production by reaction of iron ore with CH4H2-Ar gas proceeds in two stages. Stage one involves the reduction of hematite to metallic iron. The second stage is a cementation of metallic iron by methane. Cementite formation can be presented by the reaction
3Fe2O3(s) ⫹ 5H2(g) ⫹ 2CH4(g) ⫽ 2Fe3C(s) ⫹ 9H2O(g) [1] In the iron carbide process, hematite is first quickly reduced by hydrogen to magnetite, and then, magnetite is reduced further to metallic iron when the temperature is below 568 ⬚C. Methane is adsorbed on the surface of freshly formed metallic iron. Iron catalyzes the process of methane cracking with formation of carbon that is dissolved in iron. In the highly carburizing gas atmosphere, iron is supersaturated with carbon, which results in cementiite formation. However, cementite is metastable and decomposes to iron and carbon (soot). Sulphur, as a surface-active element, strongly affects the iron carbide process. A small amount of sulfur in the reaction gas retards iron ore reduction and iron cementation processes, and stabilizes iron carbide. However, mechanisms of cementite formation and the effects of sulphur on iron carbide process have not been well established. The characterization of phases formed in the iron carbide process is of importance for an understanding of the mechanisms of this process. This article discusses characterization of phases formed in the iron carbide process by X-ray diffraction (XRD), Mossbauer, X-ray photoelectron spectroscopy (XPS), and Raman spectroscopy. II. EXPERIMENTAL
EUNGYEUL PARK, Postgraduate Student, and OLEG OSTROVSKI, Professor, are with the School of Materials Science and Engineering, University of New South Wales, Sydney 2052, Australia. JIANQIANG ZHANG, Postdoctoral Research Fellow, is with the Max-Planck-Institute fu¨r Eisenforschung GmbH, D-40074 Dusseldorf, Germany. STUART THOMSON, Postdoctoral Re
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