The equilibrium constant K_Al for the reaction: 2Al+3O=Al₂O₃(s) and the first-order interaction parameter e_Al^O were estimated at 1873 K by using the values for the contents of oxygen, aluminum and other components obtained in slag-metal equilibrium experiments and those for activity of alumina, along with the respective interaction parameters. The values for log K_Al and e_Al^O were found to be 13.3±0.59 and -6.83±0.07, respectively.
Activities of slag components in the CaO-Al₂O₃-SiO₂ system were also evaluated at 1873 K from the values for nitride and sulfide capacities coupled with nitrogen and sulfur distribution ratios. These results were discussed by comparing with previous values.