Effect of Alumina on Crystallization Behavior of Calcium Ferrite in Fe(2)O(3)-CaO-SiO(2)-Al(2)O(3) System

Al(2)O(3) is a gangue component in iron ores, significantly influencing the formation and crystallization of calcium ferrite in the sintering process. But the mechanism of the Al(2)O(3) effect on the crystallization of calcium ferrite is rarely reported. In this work, a crystallization device was designed to investigate the crystallization behavior of calcium ferrite in Fe(2)O(3)-CaO-SiO(2)-Al(2)O(3) melt under non-isothermal conditions. XRD, SEM-EDS, and optical microscopy were used to identify the crystalline phase and the microstructure of samples. The result shows that the crystal morphology of SFCA changed in the order of strip, column, and needle as the Al(2)O(3) content increased. The crystallization sequence of samples containing Al(2)O(3) was observed as Ca(4)Fe(14)O(25) (C(4)F(14)) → Fe(2)O(3) → Ca(3.18)Fe(15.48)Al(1.34)O(36) (SFCA-I) → CaFe(2)O(4) (CF) → Ca(5)Si(2)(Fe, Al)(18)O(36) (SFCA) → γ-Ca(2)SiO(4) (C(2)S). The generation pathway of SFCA-I was found to be C(4)F(14) + Si(4+) + Al(3+) → SFCA-I. Increasing the cooling rate can promote the formation of C(4)F(14), SFCA-I, Fe(2)O(3) and the amorphous phase. However, it prevented the crystallization of CF and SFCA while inhibiting the transformation of β-C(2)S to γ-C(2)S. When the Al(2)O(3) content reached or exceeded 2.5 mass pct, the viscosity of Fe(2)O(3)-CaO-SiO(2)-Al(2)O(3) melt increased sharply, resulting in the decrease in the crystal size of calcium ferrite.