Effect of SiO 2 on the Formation of Acicular Calcium Ferrite in Sinter
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NTER is the main iron-bearing material in blast furnaces,[1,2] and calcium ferrite is the key bonding phase of high-basicity sinter. Calcium ferrite generally has three morphologies in sinter: massive, platy and acicular. The mechanical and reduction properties of calcium ferrites with different morphologies vary greatly.[3–6] Murakami et al.[3] found more holes around acicular calcium ferrite (ACF) than that around massive calcium ferrite and platy calcium ferrite, and a large number of holes are beneficial to the reduction of calcium ferrite by reducing gas. Compared with the massive or platy calcium ferrite, fine ACF exhibits higher microhardness and can more effectively prevent crack extension,[4] which makes the compressive strength and metallurgical properties of ACF
WEI WANG, DAIWEI YANG, ZELIN OU-YANG, RUNSHENG XU, and MINGMING SONG are with The State Key Laboratory of Refractories and Metallurgy, Wuhan University of Science and Technology, Wuhan 430081, China and also with the Hubei Provincial Engineering Technology Research Center of Metallurgical Secondary Resources, Wuhan University of Science and Technology, Wuhan 430081, China. Contact e-mails: [email protected]; [email protected] Manuscript submitted June 3, 2018.
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better than those of massive and platy calcium ferrites.[6] Furthermore, ACF can also enable the better reduction of sinter. Therefore, the formation mechanism of ACF is becoming a research hotspot. The composition of the sinter mixture and the processing conditions of sintering can affect the morphology and the quantity of ACF in sintering.[7–11] Wang et al.[7] found that the optimal temperature for the formation of calcium ferrite is 1280 C because the MgO content greater than 2.8 pct clearly decreases the number of calcium ferrite formed. Those authors indicated that the optimal basicity ratio for the development of ACF in low-silicon sinter is 2.5 to 2.8, in which the SiO2 content is 3.7 to 3.9 pct. Umadevi et al.[9] have proposed that ACF is formed at low aluminum contents of approximately 2.00 to 2.27 pct. Moreover, the solid solution of SiO2 in calcium ferrite changes the crystal structure of calcium ferrite to one conducive to the formation of ACF, and Hida et al. considered SiO2 a necessary component for the formation of ACF.[10] Several researchers[10,11] have reported that the massive and platy calcium ferrites gradually convert into ACF with the increasing amount of SiO2 in the industrial-scale sintering or sintering pot experiments. However, the effect of SiO2 on the three-dimensional (3D) morphology and growth habit of calcium ferrite has not been studied in depth, and the mechanism of formation of ACF has not been fully elucidated.
Density functional theory (DFT) software based on the first principles is now widely used in materials science research. DFT has been used to investigate the carbon-adhering reaction on the Fe3O4(111) surface in metallurgy.[12] Meanwhile, Wang et al.[13] found that mullite crystals grow at the fastest rate in
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