Activity of CaO in CaO–SiO2–Al2O3–MgO Slags

The activity of CaO in CaO–SiO2–Al2O3–MgO slags for blast furnace smelting was determined by a modified slag–metal equilibrium technique with Sn as the solvent metal and a known a(CaO) slag as the reference slag. Iso-activity contours of CaO in the CaO–SiO2–Al2O3–MgO pseudo-ternary system at w(Al2O3)=15% and w(MgO)/w(Al2O3)=0.35 were achieved from the measured values. Effects of R (basicity, R=w(CaO)/w(SiO2)), w(MgO)/w(Al2O3) and w(Al2O3) on a(CaO) were discussed. R was significant on a(CaO) and a(CaO) increased obviously with the increase of R at 1873 K. a(CaO) increased with the increase of w(MgO)/w(Al2O3) when R is 1.05 and w(Al2O3) is 15%. However, the effect of w(MgO)/w(Al2O3) on a(CaO) was not obvious for the slags with R=1.20. With the increase of w(Al2O3), a(CaO) decreased at fixed R=1.05 and w(MgO)/w(Al2O3)=0.35. When R is 1.20, a(CaO) increased with the increase of w(Al2O3).