Abstract: In accordance with the coexistence theory of slag structure, the structural units of FeO-Fe₂O₃-SiO₂ melts have been determined as simple ions Fe²⁺, O^2- and molecules SiO₂, Fe₂O₃, Fe₃O₄, Fe₂SiO₄ as well from the phase diagram and viscosity data of FeOn-SiO₂ system and phase diagram of FeOn-Fe₂O₃. On the basis of these structural units and using the standard free energies of Fe₂SiO₄ and Fe₃O₄ formation, calculating model of mass action concentrations for FeO-Fe₂O₃-SiO₂ melts has been deduced.
The calculated NFe_tO are identical with the measured αFe_tO. The mass action concentrations of NFe_tO, NSiO₂, NFe₂SiO₄ and the sum of moles Σn change with respect to the basicity ${B_1}=\frac{{\Sigma n{\rm{FeO}}}}{{\Sigma n{\rm{Si}}{{\rm{O}}_2}}}$, but themass action concentrations NFe₂O₃ and NFe₃O₄ change with respect to the basicity ${B_2}=\frac{{\Sigma n{\rm{FeO}}}}{{\Sigma n{\rm{F}}{{\rm{e}}_2}{{\rm{O}}_3}}}$, showing that the mixing of Fe₂SiO₄ and Fe₃O₄ isideal and their mutual effects are small.