Liquidus Lines in the Fe-rich Region of the FeO_x-CaO-SiO_2-Al_2O_3 System at 1 573 K under O_xygen Partial Pressures between 10 ~(-6) and 10~(-2) atm

摘要

The performance of iron ore sinter in a blast furnace such as strength and reducibility is strongly affected by the amount and the chemical composition of liquid phase in sinter during the sintering process. Thus, it is necessary to control the production of liquid phase during the sintering process. Iron ore sintering process consists of rapid heating of pulverized raw materials, partial reduction reaction of iron ores as well as liquid phase production, which are caused by combustion of cokes and suction of flaming gas. The heating time of raw materials is too short that the chemical reactions within the sinter never reach the thermodynamic equilibriums. Nevertheless, controlling the melt production could be attempted based on the thermodynamic data such as the phase diagrams. In this study, liquidus lines coexisting with iron oxides and/or 2CaOSiO_2 in the FeO_x-CaO-SiO_2 system have been measured at 1 573 K in the range of oxygen partial pressures between 10~(-5) atm and 10~(-2) atm. In addition, the effect of Al_2O_3 content on the liquidus has also been investigated as Al_2O_3 is a major gangue component affecting the quality of sinter. It has been found that the homogenous liquid region extends over a wide range of CaO/SiO_2 (C/S) ratio between 0.6 and 2 or even more for all the measurement oxygen partial pressures. It has also been found that the FeO_x content in liquid phase at C/S = 1.0 in equilibrium with solid FeO_x is almost constant to be 40-45 mass% irrespective of oxygen partial pressures. However, the FeO_x content decreases with an increase in Al_2O_3 content, indicating that the homogenous liquid region in the FeO_x-rich side becomes narrower. As a consequence, it is considered that the amount of slag melt produced in sinter during the sintering process becomes smaller with increasing Al_2O_3 content.