A Thermodynamic Model for Representation Reaction Abilities of Structural Units in Full Composition Range of Fe–Si Binary Melts Based on the Atom–Molecule Coexistence Theory

A thermodynamic model for calculating the mass action concentrations of structural units in Fe–Si binary melts based on the atom–molecule coexistence theory, i.e., the AMCT–N_i model, has been developed and verified through comparing with the reported activities of both Si and Fe in the full composition range of Fe–Si binary melts at temperatures of 1693, 1773, 1873, and 1973 K from the literature. The calculated mass action concentration N_Si of free Si or N_Fe of free Fe in the full composition range of Fe–Si binary melts has a good 1:1 corresponding relationship with the reported activity a_R,Si of Si or a_R,Fe of Fe relative to pure liquid Si(l) or Fe(l) as standard state. The calculated mass action concentration N_Si of free Si has a good corresponding relationship with the calculated activity a_%,Si of Si referred to 1 mass% of Si as standard state as well as the calculated activity a_H,Si of Si relative to the hypothetical pure liquid Si(l) as standard state. The calculated activity a_%,Si or a_H,Si of Si is much greater than the calculated mass action concentration N_Si of free Si in Fe–Si binary melts. The reaction abilities of both Si and Fe show a competitive or coupling relationship in Fe–Si binary melts at the above‐mentioned four temperatures. The calculated mass action concentrations N_i of six structural units as Fe, Si, Fe₂Si, Fe₅Si₃, FeSi, and FeSi₂ cannot show the linear relationship with the calculated equilibrium mole numbers n_i in 100‐g Fe–Si binary melts simultaneously. A spindle‐type relationship between the calculated mass action concentration N_i and the calculated equilibrium mole number n_i of FeSi and FeSi₂ in Fe–Si binary melts has been found.