Determination of activity coefficients of elements and related thermodynamic properties of Fe-Si binary melts based on the atom-molecule coexistence theory

The Raoultian activity coefficient gamma(0)(Si) of Si and gamma(0)(Fe) of Fe in the infinitely dilute solution of Fe-Si binary melts at temperatures of 1693, 1773, 1873, and 1973 K have been determined from the calculated mass action concentrations N-i of structural units in Fe-Si binary melts based on the atom and molecule coexistence theory (AMCT). The activity coefficients of elements gamma(i) relative to pure liquid matter as standard state or f(%, i) referred to 1 mass percentage as standard state or f(H, i) based on the hypothetical pure liquid matter as standard state have been obtained. The values of first-order activity interaction coefficient epsilon(i)(i) or e(i)(i) or h(i)(i) of Si and Fe related with activity coefficients gamma(i) or f(%, i) or f(H, i) of Si and Fe are also determined. The standard molar Gibbs free energy change of dissolving liquid element i(l) for forming 1 mass percentage of element i in Fe-Si binary melts have been deduced in a temperature range from 1693 K to 1973 K. The molar mixing thermodynamic properties, such as molar mixing Gibbs energy change/enthalpy change/entropy change of Fe-Si binary melts have been reliably determined in a temperature range from 1693 K to 1973 K. The excess values and excess degrees of the above-mentioned molar mixing thermodynamic properties of Fe-Si binary melts have been also determined based on ideal solution or regular solution as a basis, respectively. The determined molar mixing Gibbs energy change of Fe-Si binary melts is equal to that based on regular solution as a basis in the full composition range of Fe-Si binary melts in a temperature range from 1693 K to 1973 K. The partial mixing thermodynamic properties of Si and Fe are not recommended to obtain from the calculated mass action concentration N-Si of Si and N-Fe of Fe as well as the measured activity a(R, Si) of Si and a(R, Fe) of Fe in Fe-Si binary melts.