Thermodynamic study on the effect of CaF₂ on the nitrogen and carbon solubility in the CaO-Al₂O₃-CaF₂ slag system

The nitrogen and carbon solubilities in the CaO-Al₂O₃-CaF₂ slag system at 1723K were measured to understand the effect of CaF₂ on the nitrogen and carbon dissolution behaviour using thermochemical equilibration technique. The nitride capacity in the CaO_satd.-Al₂O₃-CaF₂ system was constant until X_Al(2)O(3)/X_CaF(2) = 0.23, followed by decrease with an increase in X_Al(2)O(3)/X_CaF(2) ratio, and then showed a constant value. The carbide capacity in the CaO_satd.-Al₂O₃-CaF₂ system also showed the similar behaviour to the nitride capacity, however, the effect of CaF₂ on the activity coefficient of nitride and carbide ions showed some differences in case of X_CaF(2) = 0.2. The effect of CaF₂ on the activity coefficient of carbide and nitride ions would not be significant in case of CaO-rich region of X_CaO/X_CaF(2) = 0.31. However, CaF₂ could be expected to affect the activity coefficient of each ion in case of the Al₂O₃-rich region, causing compensating effect of the incorporated nitride (carbide) mechanism. The relationship between nitride and carbide capacity was also discussed.