Effect of CaF2 and Li2O Additives on the Viscosity of CaO-SiO2 Na2O Slags

High aluminum containing steels react vigorously with silica-based mold fluxes to form alumina. The change in alumina content increases the viscosity and thus silica-based mold fluxes are compensated with significant amounts of Na2O, CaF2, and Li2O to ensure both lubrication and heat transfer control. Detailed viscosity studies using the rotating spindle method showed that additions of CaF2 up to 8 wt% in the CaO-SiO2-12wt%Na2O system at a constant CaO/SiO2 ratio of 0.8 decreases the viscosity by breaking the network structure of molten fluxes, but is negligible above 8 wt%. A similar modification of the network was observed for Li2O up to 2 wt%. The viscosity data was correlated with the XPS analysis and verified CaF2 and Li2O as effective in modifying complex silicate structures into simpler silicate structures depending on the availability of complex silicates and thus was limited to below certain concentrations.