In situ X-ray diffraction investigation of the formation mechanisms of silico-ferrite of calcium and aluminium-I-type (SFCA-I-type) complex calcium ferrites

Abstract

The formation mechanisms of the complex Ca-rich ferrite phase SFCA-I, an important bonding material in iron ore sinter, during heating of synthetic sinter mixtures in the temperature range 298-1 623 K in air and at pO2 = 5 × 10-3 atm, were determined using in situ X-ray powder diffraction. In air, the initial formation of SFCA-I at ∼1438 K (depending on composition) was associated with reaction of precursor phases Fe2O3, CaOFe2O3, SiO2, amorphous Al-oxide and a CFA phase of approximate composition 71.7 mass% Fe2O3, 12.9 mass% CaO, 0.3 mass% SiO2 and 15.1 mass% Al2O3. At temperatures above ∼1 453 K, the decomposition of another phase, γ -CFF, resulted in the formation of additional SFCA-I. At lower oxygen partial pressure the initial formation of SFCA-I occurred at similar temperatures and was associated with reaction between similar phases as its formation in air. However, the decomposition of γ -CFF did not result in the formation of additional SFCA-I, with the maximum SFCA-I concentration (25 mass%) lower than the values attained in air (54 and 34 mass%). Hence, more oxidising conditions appear to favour the formation of the desirable SFCA-I phase. © 2013 ISIJ.