Internally consistent thermodynamic description of three-component liquid–metal systems at high temperatures in the entire region of concentration triangle

A method is suggested for the investigation of the thermodynamic properties of ternary liquid–metal alloys at high temperatures in the entire region of concentration triangle. The method is demonstrated for a $\mathrm{Na}$–$\mathrm{K}$–$\mathrm{Cs}$ ternary system. Data are obtained for the enthalpy and Gibbs energy of formation of alloy in the temperature range of $200\le T\le1200$ K and concentration range of $0\le x_{i(j,k)}\le1$. The results reveal a very fine effect associated with the temperature rise, namely, the inversion of excess partial Gibbs energy $\Delta\bar{G}_i^*=RT\ln\gamma_i$ ($\gamma_i$ is the activity coefficient of the liquid component) and the change of sign of deviation of partial pressure, as well as of total pressure, from the respective values in accordance with Raoult's law. The obtained results may be used to interpret the available literature data on independent measurements of the saturation pressure.