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 AMC 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 1973K from the literature. 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. N-Si of free Si has a good corresponding relationship with the calculated activity a(%,Si) of Si referred to 1mass% 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. 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. 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