A study on the effect of Na₂O on the viscosity for ironmaking slags

The viscosities of CaO-SiO₂-10wt%MgO-20wt%Al₂O ₃-Na₂O slags (CaO/SiO₂=0.8-1.2, wt%Na ₂O=0-10) were measured to estimate the effect of Na₂O on the viscous behavior at elevated temperatures. The slag viscosity at 1773K decreased with increasing Na₂Ocontents, 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 O_2- 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.