Abstract
The complex calcium ferrite is the main binder phase of high basicity, high iron and low silicon sinter used in blast furnace (BF), and its formation amount and structure are important factors affecting sinter quality. This work research on the phase transformation and morphologies evolution of Fe2O3 -Fe3O4-CaO-SiO2 systems roasted 900 °C − 1200 °C in air atmosphere to understand the formation process of calcium ferrite. In CaO-Fe3O4 system, the prolonged roasting time and higher temperature promotes that CaFe5O7, CaFe3O5, and Ca2Fe2O5 gradually transformed into the stable existence of CaFe2O4. In CaO-Fe3O4 system, the higher temperature promotes that the combination of Fe3O4 and CaO formed the stable CaFe3O5 with orthorhombic structure. The replacement reaction between the newly formed CaFe3O5 phase and the unreacted CaO phase occur to form Ca2Fe2O5. In CaO-Fe3O4-SiO2 system, FeSiO3 can be combined with Fe3O4 to form Fe2SiO4 and Fe2O3. Under the action of high temperature, FeSiO3 and CaO undergo displacement reaction to form the unstable CaSiO3, the new formation of CaSiO3 can be easily combined with CaO to form the stable Ca2SiO4. With the further increase of temperature, the complex calcium ferrite is formed in calcium silicate layer. The final product complex calcium ferrite and calcium silicate exist at the same time. The formation of calcium silicate has an unfavorable effect on formation of complex calcium ferrite in the sintering process.
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