Activity of MgO in CaO–SiO₂–MgO–Al₂O₃ Melts for Blast Furnace Slag at 1873 K

Abstract

In this paper, slag-metal equilibrium experiments have been carried out for the determination of activity of MgO in CaO–SiO₂–MgO–Al₂O₃ melts for blast furnace slag at T=1873 K using Sn as metal solvent and CaF₂–MgO slag as reference slag. Based on the obtained experimental results, the iso-activity contour for CaO–SiO₂–MgO–Al₂O₃ system was plotted. The effects of R(w(CaO)/w(SiO₂)) and w(MgO)/w(Al₂O₃) on the activity of MgO was also discussed. The effects of R and w(MgO)/w(Al₂O₃) on slag structure were analyzed by Fourier transform infrared spectroscopy (FT-IR). The results show that when w(Al₂O₃)=20% and w(MgO)/w(Al₂O₃)=0.50, the activity of MgO increased with the increase of R. When w(Al₂O₃)=20% and R=1.30, the activity of MgO increased with the increase of w(MgO)/w(Al₂O₃). Through the analysis of FT-IR, the amount of free oxygen ions (O²⁻) increases with the increase of R or w(MgO)/w(Al₂O₃) in slag, and these free oxygen ions interact with the bridge oxygen (O⁰) of silicate, resulting in the gradual depolymerization of complex Si–O structure in slag.