A Study on the Effect of Na2O on the Viscosity for Ironmaking Slags

The viscosities of CaO-SiO2-10wt%MgO-20wt%Al2O3-Na2O slags (CaO/SiO2 = 0.8-1.2, wt%Na2O = 0-10) were measured to estimate the effect of Na2O on the viscous behavior at elevated temperatures. The slag viscosity at 1773 K decreased with increasing Na2O contents, which is observed in a basic oxide component. However, the FT-IR spectroscopic analysis of the slag structure seemed to verify that [AlO4]-tetrahedra depolymerized more readily than [SiO4]-tetrahedra due to ionic charge compensation which has a tendency to be more effective on [AlO4]-tetrahedra. Hence, for the present slag system, the viscosity decreased with additions of Na2O by providing network breaking O2- ions, and the charge balance by Na+ ions independently contributed to the depolymerization of the network structure of the molten slag. In addition, Na2O also lowered the critical temperature (T-CR) resulting in a larger temperature difference between the operating temperature (T-OP) and T-CR, which can enhance operational stability