Activities of FeO_1.33 in the FeO_x–CaO–SiO₂ and FeO_x–CaO–SiO₂–Al₂O₃ Slags at 1573 K Under Oxygen Partial Pressures between 10⁻⁶ and 10⁻² atm

Abstract

Qualities of sinters such as reducibility and strength are controlled by morphologies and mineral phases in iron ore sinters. Main mineral phases are hematite, magnetite and calcium ferrite. Slag phases are also included in sinters, which have been mainly liquid phases during the sintering process. Since iron ions in slags are hardly reduced to metallic irons in a blast furnace, iron oxides such as hematite and magnetite and calcium ferrite should be precipitated from molten slags during the sintering process. Precipitation of iron oxides and calcium ferrites from molten slags depends on the activity of FeO_x in molten slags from the thermodynamic view point. Therefore, the activities of FeO_1.33 have been measured over the wide ranges of chemical compositions in the single liquid phases of the FeO_x–CaO–SiO₂ and FeO_x–CaO–SiO₂–Al₂O₃ slags at 1573 K under oxygen partial pressures between 10⁻⁶ and 10⁻² atm. It has been found that the a_FeO1.33 values have maximum at the CaO/SiO₂(mass%) ratios of 0.9–1.0 and 1.3–1.4 for the samples with 35 mass%FeO_x equilibrated at P_O2 = 1.0×10⁻² atm and 1.0×10⁻⁴ atm, respectively. For the samples at P_O2 = 2.5×10⁻⁶ atm, on the other hand, a_FeO1.33 monotonically increases with increasing the CaO/SiO₂ ratio within the compositional range of the single liquid region. As for the effect of the Al₂O₃ addition on the activities, the dependency of the activity on the CaO/SiO₂ ratio becomes moderate with increasing the Al₂O₃ addition on the sample at P_O2 = 2.5×10⁻⁶ atm.