1989 Volume 29 Issue 4 Pages 318-323
The activity of Na2O in CaO-based slags has been measured employing a galvanic cell technique with a β-Al2O3 solid electrolyte. The iso-activity lines for Na2O were obtained over the liquidus composition range in the CaO–Na2O–SiO2 system at 1 400°C. The activity of Na2O in CaO–based slag is strongly controlled by the SiO2 content in slag and the activity coefficient of Na2O increases as the CaO content increases. The activity of Na2O in a 50%CaO–40%Al2O3–10%SiO2 (typical ladle slag composition) is extremely high. At a Na2O concentration of about 8 wt% in this slag, the activity of Na2O is nearly equal to that of 50wt%Na2O–SiO2 slag at the same temperature. The Richardson solution model fits the experimental data well and this model was used to compute the activity of CaO in these systems. The addition of Na2O significantly increases the activity of CaO.