Abstract
The equilibrium relationship of the Fe-Ca-O system was discussed in terms of Gibbs free energy changes and interaction parameters to explain the difference between the thermodynamically calculated solubility product of CaO in molten iron and the measured one. It was found that the strong affinity between calcium and oxygen accounts for the difference while there is some uncertainty for the free energy change of solution of calcium into iron. Second order interaction parameters have to be introduced for consistent description of the equilibrium of the Fe-Ca-O system although the contents of calcium and oxygen are very low.
