Thermodynamic behaviour of carbon in CaO-SiO₂ slag system

In order to understand the thermodynamic behaviour of carbon in steelmaking slag at high temperature, the carbon dissolution into CaO-SiO₂ slag system has been investigated including the effects of temperature and slag components on the carbon dissolution reaction. It was found that carbide solubility in the CaO-SiO₂ slag decreased with increasing oxygen potential to confirm the theoretical relationship of -1/2, which reflected the ionic exchange reaction mechanism between carbon and oxygen ions. Carbide solubility in slag as a function of slag basicity for various slag systems appeared to confirm this mechanism. This reaction mechanism implied that the carbide dissolution proceeded due to the reaction of solid carbon and oxygen ions supplied from (CaO) in slag. The oxygen ion appears to be the driving force as it is influenced by the slag components as well as the temperature as shown in the concept of the carbide capacity of slag. The solubility of carbide in the CaO-SiO₂ slag increased with the addition of CaF₂; the role of CaF₂ for carbide dissolution into slag could be speculated to have complex effects on indirect increase in basicity in spite of (CaO) dilution. Substitution of CaO by MgO decreased the solubility of carbide in the CaO-SiO₂-MgO slag, possibly caused by the relatively low electro-negativity of MgO.