Thermodynamic study of MnO-SiO2-Al(2)O3 slag system: Liquidus lines and activities of MnO at 1823 K

Abstract

The liquid MnO-SiO-Al2O3 system was studied at 1823 K by equilibrating MnO-SiO2-Al2O3 melts of different compositions with Pt-Mn alloys and an oxygen-bearing gas phase. Liquid compositions for cristobalite saturation were determined at 1823 K. A new liquidus for the cristobalite primary field is proposed. The activity of Mn in the Pt-Mn alloy at 1823 K can he represented by the following equation: ln gamma(Mn) = -9.285(1 - X-Mn)(2) - 2.0791 The MnO activity was measured in different melt compositions and MnO isoactivity lines were determined. It was found that the MnO activity is relatively insensitive to the SiO2/Al2O3 ratio, but increases sharply above the MnO mole fraction of 0.5. In the low-MnO-concentration range (alpha(MnO) < 0.15), the quadratic formalism expressed by the following equation is proposed to represent the MnO activity: RT ln gamma(MnO) = -75,310x(SiO2)(2) - 83,680x(AlO1.5)(2) - 31,380x(SiO2)x(AlO1.5) + 2194 J mol(-1) If the MnO activity exceeds the aforementioned limit, the modified quasi-chemical model is recommended.