Thermodynamic properties of iron silicides and phase equilibria in {(1 − x)Si + xFe}

Abstract

A Knudsen-effusion technique with mass-spectrometric analysis of evaporation products has been employed to determine thermodynamic properties of {(1 − x)Si + xFe} alloys. The temperature and mole-fraction ranges investigated were T = 1351 K to 1664 K and x = 0.349 to 0.646. Alloys with compositions belonging to each of the two equilibrium fields of two solid phases and to the regions of equilibrium between FeSi and liquid phase were studied. Activities and partial molar thermodynamic functions of Fe and Si were calculated from the values of pFe and pSi found. The minimal values of ΔfGm and ΔfHm with respect to their dependence on mole fraction were found at T = 1423 K to correspond to iron monosilicide. Computations of a number of phase equilibria in {(1 − x)Si + xFe} have been carried out to prove the reliability of the thermodynamic information acquired. Temperature dependences of the molar Gibbs energies of formation of the intermediate phases established in the present work as well as thermodynamic characteristics of formation of the associative complexes reported previously were used for the purpose. The coordinates of melting temperatures of iron silicides were found to coincide with those recommended in the literature.