A thermodynamic model for predicting manganese distribution ratio L_Mn and manganese capacity C_Mn of CaO–SiO₂–FeO–MgO–MnO–Al₂O₃ slags, i.e. IMCT-L_Mn and IMCT-C_Mn models, has been developed by using a thermodynamic model for calculating mass action concentration of ion couples or structural units in the slags based on the ion–molecule coexistence theory (IMCT). The developed IMCT-L_Mn and IMCT-C_Mn models have been verified with the experiment results of CaO–SiO₂–FeO–MgO–MnO–Al₂O₃, CaO–SiO₂–MgO–FeO–Fe₂O₃–MnO–P₂O₅, CaO–SiO₂–MgO–FeO–Fe₂O₃–MnO–Al₂O₃–P₂O₅ slags reported by different researchers, a total of 200 industrial measurements with large compositional variations and predicted results by summarised five L_Mn models and two C_Mn models. The developed thermodynamic model for calculating manganese distribution ratio can determine quantitatively the respective manganese distribution ratio L_Mn,i and the respective manganese capacity C_Mn,i of four demanganisation products as MnO, , and . A significant difference of demanganisation abilities among FeO, FeO + Al₂O₃ and FeO + SiO₂ can be found as 98, 1.8 and 0.2%. By comparing binary and complex basicity, the optical basicity is recommended to describe the relationship between basicity and manganese distribution ratio. With the aid of the current model, the co-effects of the ratio and optical basicity on the L_Mn and C_Mn of CaO–SiO₂–FeO–MgO–MnO–Al₂O₃ slags are investigated.

In the current study, the thermodynamics of the slag-metal equilibrium reaction between Inconel 718 Ni-based alloy and CaF₂-CaO-Al₂O₃-MgO-TiO₂ electroslag remelting (ESR)-type slags were systematically investigated in the temperature range from 1773 to 1973 K (1500 to 1700 °C). The equilibrium Al content increased with increasing temperature, whereas the equilibrium Ti content decreased with increasing temperature at a fixed slag composition. The important factors for controlling the oxidation of Al and Ti in the Inconel 718 superalloy were TiO₂ > Al₂O₃ > CaO > CaF₂ > MgO in ESR-type slag and Al > Ti in a consumable electrode. The conventional method of sampling by means of a quartz tube could result in contamination of the molten metal and changes in the size of the “special reaction interface”. Therefore, a novel method was used in the present study to investigate the slag-metal reaction kinetics to accurately obtain the kinetic parameters. The mass transfer coefficient was determined by coupling with the kinetic model derived from the assumption that the reaction rate ([Al] + (TiO₂) = [Ti] + (Al₂O₃)) was controlled by the mass transfer of [Ti], [Al], (TiO₂) and (Al₂O₃) in the boundary layer, respectively.

A thermodynamic model (IMCT-L_Mn) for calculating manganese distribution ratio between CaO–SiO₂–MgO–FeO–MnO–Al₂O₃–TiO₂–CaF₂ slags and carbon saturated liquid iron have been developed based on the ion and molecule coexistence theory. The predicted manganese distribution ratio shows a reliable agreement with the measured ones. With the aid of the IMCT-L_Mn model, the respective manganese distribution ratio of (Mn²⁺ + O²⁻), MnO·SiO₂, 2MnO·SiO₂, MnO·Al₂O₃, MnO·TiO₂, and 2MnO·TiO₂ are investigated. The results indicate that the structural units SiO₂ + FeO play a key role in CaO–SiO₂–MgO–FeO–MnO–Al₂O₃–TiO₂–CaF₂ slags in demanganisation process in the course of hot metal treatment at 1673 K. The manganese distribution ratio at a given binary basicity range increases with CaF₂ content, while that decreases with TiO₂ content at different binary basicity scopes, which demonstrate that high Mn in the metal is favoured by TiO₂ content. In the present study, various critical experiments are carried out in an effort to clarify the effect of temperature on demanganisation ability, indicating that the lower temperature of molten metal is, the faster the rate of demanganisation reaction is and the shorter the thermodynamic equilibrium time is and the lower end-point Mn content is. It can be deduced from the obtained experimental results that the greater oxygen potential of slags or iron-based melts, lower content of basic oxides in slags, and lower temperature at reaction region is benefit for demanganisation reaction.