The Formation Process of Silico-Ferrite of Calcium (SFC) from Binary Calcium Ferrite
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SINCE the 1960s the composition and structure of silico-ferrite of calcium and aluminum (SFCA) has been determined by some scholars.[1–9] Ikeda et al.[10] and Inoue and Ikeda[11] found that the composition of Si-rich calcium ferrite in the CaO-SiO2-Al2O3-Fe2O3 system consisted of a CaOÆ3Fe2O3-CaOÆ3Al2O3-CaOÆSiO2 ternary system and the solid solution limit of SiO2 is 12.5 mol pct. The structure (triclinic P1, a = 10.057, b = 10.567, c = 9.092 A˚, a = 95.45, b = 114.33, c = 64.13 deg) was determined earlier. The SFCA with the type of a lowFe form was known when its structure (triclinic P1; a = 9.06, b = 10.02, c = 10.92 A˚, a = 60.30, b = 73.68, c = 65.81 deg) was determined by Hamilton et al.[12] The SFC phase was identified by Hamilton et al., who recognized an alumina-free equivalent of SFCA and the compositional range for the SFC along the pseudobinary. Mumme CaOÆ3Fe2O3-4CaOÆ3SiO2 et al.[13] found in 1998 that the second SFCA type is a high-Fe, low-Si form called SFCA-I (triclinic P1; a = 10.43, b = 10.61, c = 11.84 A˚, a = 94.14, b = 111.35, c = 110.27 deg). In 2003, SFCA-II (triclinic P1; a = 10.338, b = 10.482, c = 17.939 A˚, a = 90.384, b = 89.770, c = 109.398 deg), which is a third type of SFCA, was also reported by Mumme.[14] Pownceby
XIANG DING, Ph.D. Candidate, and XING-MIN GUO, Professor, are with the State Key Laboratory of Advanced Metallurgy and School of Metallurgical and Ecological Engineering, University of Science and Technology Beijing, Beijing 100083, P.R. China. Contact e-mail: [email protected], [email protected] Manuscript submitted November 29, 2012. METALLURGICAL AND MATERIALS TRANSACTIONS B
et al.[15–18] have systematically studied the solid-solution limits and thermal stability of SFC and SFCA, respectively, and they confirmed that chemical substitution in the quaternary system follows the coupled substitution mechanism 2(Fe3+, Al3+) M (Ca2+, Fe2+) + Si4+. The composition formed is similar to the CaOÆ3Fe2O3CaOÆ3Al2O3-4CaOÆ3SiO2 ternary system structure. Sugiyama et al.[19] reported that Mg-rich SFCA (SFCAM) phase has the formula of Ca2(Ca, Fe, Mg, Al)6(Fe, Al, Si)6O20 and the crystal structures are Ca2(Ca0.10Mg1.20Fe5.55Si1.50Al3.65)O20 (triclinic P1; a = 8.848, b = 9.812, c = 10.403 A˚, a = 64.35, b = 84.19, c = 66.27 deg) and Ca2(Mg2.00Fe4.45Si2.15Al3.40)O20 (triclinic P1; a = 8.928, b = 9.823, c = 10.389 A˚, a = 64.41, b = 83.90, c = 65.69 deg). The SFC-phase, SFCA-phase, and SFCAM-phase are the major bonding phases in iron ore sinter; the composition of them mainly is a ternary system structure that as reported at above, and they have the similar crystal structure that belongs to triclinic crystal system. At the same time, Hida and colleagues[20–22] and Hsieh and Whiteman[23] studied the formation mechanism of SFCA. More recently, the formation mechanism of SFCA was confirmed by Scarlett et al.[24,25] and Webster et al.[26] They found that Fe2O3 reacted with CaO at temperatures ~1023 K to 1053 K (750 C to 780 C) to form C2F. The C2F phase then reacted with Fe2O3 to produce CF. Quar
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