Activity Coefficient of Silicon and its Interaction Coefficients in Fe–C–Si Melt at 1773 K

Abstract

Fe–C–Si ternary melt was studied experimentally by establishing an iso-silicon-activity state for ternary samples through a common silver bath. A method for evaluating a set of self-consistent activity interaction coefficients in Fe–i–j systems has been proposed. Its application to Fe–C–Si ternary melt yields
ln γ_Si⁰=−7.21, ε_Si^Si=17, ρ_Si^Si=−8, ε_Si^C=6.5, ρ_Si^C=−4 and ρ_Si^C,Si=−5,
and hence the activity coefficient of silicon can be expressed as:
ln γ_Si=−7.21+17X_Si−8X_Si²+6.5X_C−4X_C²−5X_SiX_C.
It has been shown that Darken’s ternary quadratic equations are incapable of evaluating the activity coefficients of silicon and carbon in Fe–C–Si melt due to the inconsistency of α_Si-C. However, in combination with eqs. (18) and (23) in the text, the ternary quadratic formalism becomes useful for estimating logγ_Si along each iso-silicon-activity line.