Insight of Iron Whisker Sticking Mechanism from Iron Atom Diffusion and Calculation of Solid Bridge Radius
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DEFLUIDIZATION resulting from sticking during the iron ore reduction process was a key problem that hindered fluidization during iron-making technology industrialization. Research suggested that the hook effects of the iron whisker resulted in iron ore sticking during the gas reduction process.[1–3] According to results from M. Schiller,[4] there are three kinds of states for fresh metal iron during iron ore reduction, including dense iron, iron whisker, and porous sponge iron. An iron whisker was a kind of metallic iron, with a bigger length–diameter ratio, which had maybe some effects on iron ore sticking. Our previous research suggested that the nano- and microstructure on the surface of fresh reduction metallic iron was an important factor that resulted in iron-iron sticking during the reduction process[5]; thus, the morphology of fresh metallic iron maybe had some effects on sticking. The iron whisker was a type of special nano- and microstructure. Sticking maybe not only resulted from XUZHONG GONG, Associate Professor, and ZHI WANG, Professor, are with the National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Institute of Process Engineering, Chinese Academy of Sciences, Beijing 100190, P.R. China. Contact e-mail: [email protected] BEN ZHANG, Assistant Professor, is with the National Engineering Laboratory for Hydrometallurgical Cleaner Production Technology, Institute of Process Engineering, Chinese Academy of Sciences, and also with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing, Beijing 100083, P.R. China. ZHANCHENG GUO, Professor, is with the State Key Laboratory of Advanced Metallurgy, University of Science and Technology Beijing. Contact e-mail: [email protected] Manuscript submitted April 28, 2014. Article published online July 29, 2014. 2050—VOLUME 45B, DECEMBER 2014
the hook of the iron whisker but also from its other features. The formation of iron whiskers was related to the reduction conditions. The iron whisker structure obtained by CO reduction is easier than that by H2 reduction.[6] And the iron whisker was formed under a high temperature and a low reduction potential condition.[4] The reduction process was controlled by the interface chemical reaction at this condition; in other words, the production rate of iron atoms by reduction was negligible compared with their diffusion rate. The nucleation occurred at the surface site that had the lowest critical iron activity, and the produced iron atom diffused quickly to the site for outside of the iron nucleus, resulting in low iron activity in the bulk so that no other nucleus could be formed.[7] Therefore, an iron whisker was formed. That is to say, the diffusion activity of the Fe atom during the formation process of iron whiskers was very strong, so the sticking maybe resulted from the iron atom diffusion to form a connection when iron whiskers contact. Additionally, our preliminary research suggested that the tiny iron grain on the surface of the particles led
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