The effects of alkaline earth metal ions and halogen ions on the chromium oxide activities in alkaline earth metal oxide-halide-Cr2O3 system fluxes

The solid electrolyte cell — Mo|Cr + Cr₂O₃‖ZrO₂(MgO)‖{Cu-Cr}_alloy + (Cr₂O₃)_fluxes|Mo+ is used at 1673 K to determine Cr₂O₃ activities in MO-MX ₂-Cr₂O₃ (M = Ca²⁺, Ba²⁻, X = F⁻ or Cl⁻) ternary fluxes, which are in equilibrium with the copper-chromium binary alloy. The ternary isothermal phase diagrams of CaO-CaF₂-Cr₂O₃ and BaO-BaCl₂-Cr₂O₃ system fluxes are inferred on the basis of the experimental results and binary phase diagrams. The results indicate that Cr₂O₃ activities in all fluxes always decrease with the increase of the X _MO /X _MX2 ratio. Partial replacement of BaO in BaO-BaF₂-Cr₂O₃ fluxes by CaO is acceptable for economy and efficiency considerations. At the same time, partial substitution of BaO for CaO in CaO-CaF₂-Cr₂O₃ fluxes is advantageous for phosphorus removal and chromium retention as a result of the increased Cr₂O₃ activities, increased basicities, and widening of the liquid zones. Compared to those in BaO-BaF₂-Cr₂O₃ fluxes, Cr₂O₃ activities in CaO-CaF₂-Cr₂O₃ fluxes approximately follow the same curve as the former, although the position and the width of the liquid zones are considerably different, and activities in BaO-BaCl₂-Cr₂O₃ fluxes are higher at the lower Cr₂O₃ content, or vice versa. The activity coefficients of Cr₂O₃ in the fluxes decrease with the increase of the X _MO /X _{MX 2} ratios.