Stability of SFCA-I in CaO–Fe<sub>2</sub>O<sub>3</sub>–Al<sub>2</sub>O<sub>3</sub> and CaO–Fe<sub>2</sub>O<sub>3</sub>–Al<sub>2</sub>O<sub>3</sub>–SiO<

SFCA-I, a form of silico-ferrite of calcium and aluminum (SFCA) in CaO-Fe2O3-Al2O3-SiO2 system, is the key bonding phase for iron ore sintering and significantly influences sinter quality and carbon emissions in sintering process. The phase equilibria characteristics of SFCA-I are essential for the design and operation of iron ore sintering. However, most SFCA-I samples synthesized in laboratories currently lack SiO2, indicating that the composition of SFCA-I lies within the CaO-Fe2O3-Al2O3 ternary system. In this study, the solid solution series, solid solution limits, and stable region of SFCA-I at 1200°C in air in CaO-Fe2O3-Al2O3 and CaO-Fe2O3-Al2O3-SiO2 systems were revealed via phase equilibrium tests. The results indicate that the upper and lower solid solution limits of Al2O3 in SFCA-I are 1.31wt% (i.e., 1.67mol%) and 7.65wt% (i.e., 9.10mol%) at 1200°C in CaO-Fe2O3-Al2O3 system. With the increase of Al2O3 content, the upper limit of SiO2 solid solution in SFCA-I is gradually decreased. The upper limit of SiO2 solid solution in SFCA-I reaches a minimum value of 0.686wt% when Al2O3 content is 7.62wt% at 1200°C in CaO-Fe2O3-Al2O3-SiO2 system. In addition, the XRD results prove that SFCA belongs to the solid solution of C(A,F)3 series. The other phases encountered in the tests include Fe2O3, CF, C(A,F)3, C(A,F)2 and C2(A,F). The relevant schematic and calculated phase diagrams are constructed. The position of SFCA-I in the CaO-Fe2O3-Al2O3 ternary system and the relations among SFCA, SFCA-I and the surrounding phases are presented.