The intermediate solid solution (ISS) of the Cu-Fe-S system: Phase equilibria calculation at elevated temperatures based on Gibbs energy modeling

The phase equilibria of the Cu-Fe-S system are calculated from liquidus to medium temperatures based on Gibbs energy modeling of the intermediate solid solution (ISS). The compound energy formalism is used for a suitable thermodynamic model to account for the pronounced solid solution character of ISS. The obtained Gibbs energy as a function of composition and temperature allows the computation of complex phase relations with high-temperature modifications of bornite and pyrrhotite, pyrite and chalcopyrite, of which a Gibbs energy expression as a function of temperature is also provided. For the first time, a direct comparison is made public between the well-known experimental isoplethal phase diagram along the CuFe–S join, which was provided more than fifty years ago by Barton (1973) , and a thermodynamically computed phase diagram section. A detailed comparison with experimental phase equilibria data on the homogeneity range of ISS at 800 °C, 760 °C, 700 °C and 600 °C with calculated results is carried out. In total three isoplethal and four isothermal sections of the Cu-Fe-S phase diagram are computed, and the agreement with experimental data available in the literature ranges from fair to very satisfactory. • A new Gibbs energy model for the intermediate solid solution (ISS) of the Cu-Fe-S system allows the calculation of complex phase relations over the complete liquidus and solidus • The well-known experimental isoplethal phase diagram along the CuFe–S join by Barton (1973) can be compaed with a thermodynamically computed phase diagram section, published for the first time • New contribution to clarify the stability of Cu-Fe-S phases in equilibria with ISS at 800 °C to 600 °C are offered on a quantitative thermodynamic basis • First adequate reproduction of the homogeneity range of ISS by thermodynamic computations in line with experimental data