Effect and Mechanism of Alumina on the Morphology and Mechanical Properties of Calcium Ferrite
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INTRODUCTION
A high-basicity sinter is an important iron-bearing raw material in blast furnaces in the Asia-Pacific region.[1] The quality of the sinter depends on its strength and reduction performance.[2] The strength and reducibility of the sinter are mainly affected by the quantity, morphology, and form of the different minerals in it.[3–5] The quality of the sinter is also affected by the sintering process and composition. Previous studies[3,6,7] showed that calcium ferrite was the most important binding phase in sinters due to its relatively low melting point, high strength, and improved reducibility. The alumina content in iron ore has an obvious effect on the strength and reducibility of the sinter, especially its low-temperature reduction degradation.[8,9] Extensive work on the effects of alumina on the sinter structure
DAIWEI YANG, WEI WANG, JINGXUAN LI, RUNSHENG XU, and XIANZHEN WANG are with the 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-mail: [email protected] GEOFF WANG is with the School of Chemical Engineering, University of Queensland, Brisbane 4067, Australia. Manuscript submitted July 10, 2019.
METALLURGICAL AND MATERIALS TRANSACTIONS B
indicated that small amounts of Al2O3 in sinter could improve the formation and stability of complex calcium ferrite and improve the overall reduction performance of the sinter.[10,11] A low-alumina sinter showed improved productivity and strength, but it had a decreased reduction degradation index (RDI).[12,13] Jin et al. found[14] that the melting temperature of the CaOFe2O3-SiO2-Al2O3 system was reduced upon the addition of a small amount of Al2O3, and the liquid phase fluidity increased. However, when the Al2O3 content was too high, the melt temperature increased, and the fluidity decreased. Sinha et al.[12] determined that Al2O3 deteriorates the strength and toughness of calcium ferrite phases by increasing their hardness and thus generating cracks. Cores et al.[11] and Umadevi et al.[15] believed that increasing the Al2O3 content exacerbates the chalking phenomenon, which does not improve the quality of sinter. Increasing the content of Al2O3 promotes the formation of plate-like calcium ferrite, which produces a compressive stress and reduces the ability of sinter to resist crack propagation. Al2O3 is mainly present in composite calcium ferrite and as a glass phase in sinters.[3,10,16–18] Al2O3 is necessary for the formation of silico-ferrite of calcium and aluminum (SFCA)[19] and has an important influence on its morphology and metallurgical performance. Many studies[20–23] have shown that there are mainly two kinds of complex calcium ferrite in a basic sintered ore: SFCA (low Fe, high Si, and high Al) and SFCA-I (high Fe, low Si, and low Al). The cross-sectional area of
SFCA-I is usually acicular,
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