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, 10-18 mass% Al ₂O₃, 3.5-10 mass% MgO and 5 mass% FeO. The bosh slag with 10 mass% Al₂O₃ content had the lowest melting temperature and the widest solid-liquid coexisting region at about 5 mass% MgO, while in case of 14 mass% Al₂O₃, an increase in a MgO content from about 3.5 to 10 mass% raised the melting point of bosh slag. The viscosity of bosh slag also exhibited a minimum value at about 7 mass% MgO at temperatures above 1 723 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 10 mass%, respectively, for high pulverized-coal ratio (PCR) and low slag volume operations in blast furnace.