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Keywords:

  • Fe–Si binary melts;
  • activity of silicon;
  • activity of iron;
  • mass action concentration;
  • reaction ability/potential;
  • thermodynamic model;
  • structural units;
  • atom and molecule coexistence theory (AMCT)

Abstract

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–Ni 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 NSi of free Si or NFe of free Fe in the full composition range of Fe–Si binary melts has a good 1:1 corresponding relationship with the reported activity aR,Si of Si or aR,Fe of Fe relative to pure liquid Si(l) or Fe(l) as standard state. The calculated mass action concentration NSi 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 aH,Si of Si relative to the hypothetical pure liquid Si(l) as standard state. The calculated activity a%,Si or aH,Si of Si is much greater than the calculated mass action concentration NSi 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 Ni of six structural units as Fe, Si, Fe2Si, Fe5Si3, FeSi, and FeSi2 cannot show the linear relationship with the calculated equilibrium mole numbers ni in 100-g Fe–Si binary melts simultaneously. A spindle-type relationship between the calculated mass action concentration Ni and the calculated equilibrium mole number ni of FeSi and FeSi2 in Fe–Si binary melts has been found.