Influence of MgO and Al2O3 contents on viscosity of blast furnace type slags containing FeO

The viscosities of CaO-SiO2-Al2O3-MgO-FeO slag were measured under conditions of C/S=1.35-1.45, 10-18mass% Al2O3, 3.5-10mass% MgO and 5mass% FeO. The bosh slag with 10mass% Al2O3 content had the lowest melting temperature and the widest solid-liquid coexisting region at about 5mass% MgO, while in case of 14mass% Al2O3, an increase in a MgO content from about 3.5 to 10mass% raised the melting point of bosh slag. The viscosity of bosh slag also exhibited a minimum value at about 7mass% MgO at temperatures above 1723 K. However, it was not significantly changed with varying MgO content. On the hand, with increasing Al2O3 content, the viscosity of bosh slag increased at a fixed C/S and MgO content. Based on the melting temperature and the behavior of viscosity at a fixed temperature, it could be proposed that the MgO and Al2O3 contents in bosh slag should be maintained around 5 and 10mass%, respectively, for high pulverized-coal ratio (PCR) and low slag volume operations in blast furnace.