Activities of FeO in CaO-Al₂O₃-SiO₂-FeO and CaO-Al₂O₃-CaF₂-FeO Slags

Abstract

Activity coefficients of FeO in molten CaO-Al₂O₃-SiO₂-FeO (<5 %) slags were determined at 1673 and 1873 K by equilibrating the slags with copper-iron alloys in a controlled oxygen partial pressure (P_O2=5.71×10^-12 atm at 1673 K, 1.90×10^-10 atm at 1873 K). Activity coefficients of iron in copper-iron (<4 %) alloys at 1673 K were preliminarily determined by controlling the activity of iron using FeO·Cr₂O₃ saturated with Cr₂O₃ in a various oxygen partial pressures (P_O2=3.66×10^-12-9.14×10^-11 atm).
It was found that the activity coefficients of FeO obey Henry's law, and have the maximum value when the ratio of N_CaO/N_SiO2 is about 2 at a constant Al₂O₃ content. The activity coefficients of iron in copper-iron alloy referred to pure liquid were determined as

lnγ_Fe=2.76-11.3N_Fe.

The effect of a CaF₂ addition to the CaO-Al₂O₃-FeO system on the activity coefficient of FeO was also investigated at 1723 K.