The Solid Solution State and the Crystal Structure of Calcium Ferrite Formed in Lime-fluxed Iron Ores

Abstract

The solid solution state and the crystal structure of calcium ferrite formed in lime-fluxed iron ore sinters and pellets have been extensively investigated in the synthetic quaternary CaO-SiO2-Al2O3-Fe2O3 system.The results obtained are summerized as follows:(1) The calcium ferrite is a solid solution consisting of CaSiO3-Ca(Fe, Al)6O10. The SiO2 component is found to dissolve into the ferrite continuously up to 12.5 mol% at 1250°C and the formation of SiO2-poor ferrite requires an increase in Al2O3 content. On the other hand there exists a lower limit of CaO·3Al2O3 component at about 2 mol% for the formation of the ferrite. It is also confirmed that the dissolution of SiO2 and Al2O3 components is the essential condition for the formation of the ferrite in the light of phase boundary between hematite and calcium ferrite determined in the present study.(2) Powder and single crystal x-ray diffraction studies show that these ferrite phases crystallize in triclinic throughout the wide range solid solubility of SiO2 and Al2O3 and the lattice parameters of the most SiO2-rich ferrite are found to be a=10.057 Å, b=10.567 Å, c=9.092 Å, α=95.45°, β=114.33°and γ= 64.13°. From Patterson synthesis of measured structure factors, a considerable number of Fe3+ ions are suggested to be situated in the tetrahedral sites. It is proposed that the structure may be stabilized by substituting the Fe3+ ions in the tetrahedral sites by Si4+ and Al3+ ions with smaller ionic radii.