Effect and mechanism of alumina on the morphology and mechanical properties of calcium ferrite

AlO greatly influences the formation of complex calcium ferrite, which is the main binder and iron-bearing phase in sinter. Experiments were carried out in air at 1200\ua0°C with different amounts of AlO mixed with CaO·FeO (calcium ferrite). The samples contained two phases: CaFeO and CaFeAlO (CFA). The results showed that the morphology of the complex calcium ferrite was massive (w(AlO) = 0 pct), columnar and plate-like (w(AlO) = 0.5 and 1 pct), and acicular and plate-like (w(AlO) = 2, 3, and 5 pct). A small amount of AlO solid solution in CaFeO increased the preferred orientation of the crystal. The gradual increase in AlO in the sintered samples caused the complex calcium ferrite composition to be closer to that of silico-ferrite of calcium and aluminum (acicular SFCA-I). When AlO dissolved into calcium ferrite, complex calcium ferrite was formed, which increased the hardness of the sample. The fracture toughness of the sample increased with increasing AlO content from 0 to 2 pct, possibly due to a decrease in grain size. When the AlO content exceeded 3 pct, AlO dissolved into calcium ferrite and decreased the fracture toughness of the sample