Effect of Al2O3/SiO2 ratio on morphology of complex calcium ferrite

Al2O3 and SiO2 greatly influence the formation of complex calcium ferrite, which is the main bonding phase in high basicity sinters. The effects of Al2O3/SiO2 ratios on the morphology of complex calcium ferrite were studied. The main mineral phases in the samples with different Al2O3/SiO2 ratios were CaFe2O4 with a solid solution of Si or Al atoms and the silico-ferrite of calcium and aluminum. The results showed that the morphology of the complex calcium ferrite changed from lumpy to plate-like and acicular with increases in the SiO2 content and the Al2O3/SiO2 ratio. When the content of SiO2 was 4 wt.%, the main calcium ferrite morphology was acicular, and the number of macropores in the samples increased with the Al2O3/SiO2 ratio increasing. The first-principles analysis of the calcium ferrite crystal structure showed that adding SiO2 and Al2O3 changed the growth mechanism of the CaFe2O4 crystal, promoting the formation of platy and acicular complex calcium ferrite. The size of calcium ferrite was significantly smaller due to the increase in CaO–Fe2O3–SiO2–Al2O3 viscosity with increasing the Al2O3/SiO2 ratio.