Effect of MgO on Formation and Crystallization Behaviors of Calcium Ferrite during Heating and Cooling Processes

Abstract

MgO is one of essential component in blast furnace slag for improving the fluidity and desulfurization. Generally it is added via sintering process. It has been also proved in practice that the addition of MgO affects the quality of sinter significantly. However, the effect of MgO on formation and crystallization behaviors of calcium ferrite in sintering had been scarcely discussed. In this work, the crystalline products in CaO–Fe₂O₃ system with different content of MgO were identified by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS). In order to follow the reactions during heating and cooling, differential scanning calorimetry (DSC) was also conducted. It was found that addition of MgO restrained the formation of CaFe₂O₄ leading to the decrease in content of original melt during sintering process. The contents of Ca₂Fe₂O₅ and solid solution of magnetite (magnetite s.s) were increased and the crystallization of Ca₂Fe₂O₅ was also promoted with increasing MgO. Compared with forming Ca₂Fe₂O₅, addition of MgO facilitated to form magnetite s.s. Content of initial liquid phase was decreased with increasing MgO, whereas new liquid phase was generated at 1609 K when the content of MgO exceeded 7 mass%, due to the reaction between Ca₂Fe₂O₅ and magnetite.