Thermodynamic Activity of B₂O₃ in CaO–SiO₂–Al₂O₃–B₂O₃–MnO–MgO Molten Slags at 1723 K

This study aimed to investigate the thermodynamic characteristics of the reaction between Al and B₂O₃ in the continuous casting process of high-aluminum steel. The activity coefficient of B₂O₃ in molten slag of (31.1 to 58.4) pct CaO–(0.2 to 16.7) pct SiO₂–(14.7 to 49.2) pct Al₂O₃–(0 to 30.3) pct B₂O₃–(0 to 10.5) pct CaF₂–(2.1 to 4.7) pct MgO–(0 to 1.8) pct MnO slags was measured at 1450°C using B equilibrium experiments between liquid copper and molten slag in a graphite crucible under the mixed gas atmosphere of CO and Ar. The effects of B₂O₃, Al₂O₃, SiO₂, and CaF₂ and the basicity (B = mass pct CaO/(mass pct SiO₂+mass pct Al₂O₃) on the activity coefficient of B₂O₃ in molten slag were discussed. Regression analysis was used to investigate the quadratic relationship between the activity coefficient of B₂O₃ and the concentrations of components in the slag. The results indicated that (a) the activity coefficient of B₂O₃ increased with an increase in B₂O₃ when B₂O₃ > 7 pct and B < 1, but decreased when B₂O₃ > 7 pct and B > 1. (b) When B > 0.9 and Al₂O₃ > 26 pct, the activity coefficient of B₂O₃ went up with the increase of Al₂O₃, but decreased when B < 0.9. (c) When B = 0.93 to 0.97, B₂O₃ = 9.1 to 9.5 pct, and CaF₂ < 11 pct, the activity coefficient of B₂O₃ decreased with an increase in CaF₂. (d) When B = 0.8 to 1.3, the activity coefficient of B₂O₃ increased with the increase of the basicity B. These findings provide insight into the factors affecting the activity coefficient of B₂O₃ in the molten slag and contribute to the optimization of the continuous casting process of high-aluminum steel.