Thermodynamics of antimony-selenium alloys formation and evaporation

The thermodynamic functions of alloy formation and evaporation were considered for two particular systems - Sb - Sb2Se3 and Sb2Se3- Se in connection with the presence of congruently melting compound Sb2Se3 in the antimony-selenium system. The calculations are based on the partial vapor pressure values of the components forming the particular systems. The thermodynamic activity of antimony selenide and selenium as the most volatile components in the systems was calculated based on the saturated vapor pressure values of antimony selenide over the Sb - Sb2Se3 and selenium melts over Sb2Se3- Se liquid alloys determined by the boiling point method (isothermal variant). Similar functions of the low volatile components in the above systems: Sb in the first system and Sb2Se3 in the latter one was calculated by numerical integration of the Gibbs-Duhem equation using the substitution proposed by Darken. The partial pressures of antimony selenide and antimony over Sb - Sb2Se3 and Sb2Se3- Se melts were approximated by temperature-concentration relationships. The system is distinguished with a positive deviation from ideality due to the presence of a delamination region in the first system. The partial and integral entropies and enthalpies of the formation of liquid alloys were calculated based on the values of component activities found as the ratio of the partial vapor pressure of an element or compound above the solution to the saturated vapor pressure of a pure element or compound. The partial and integral functions of alloy formation are presented in the form of graphical dependences on the selenium amount in the melt. The obtained thermodynamic constants will replenish the physical and chemical data base and will be used to calculate the boundaries of the vapor- liquid equilibrium fields on the diagram of state, allowing to determine the possibility and completeness of distillation separation of molten systems.