The activity of the components of a $\mathrm{Na}$–$\mathrm{K}$–$\mathrm{Cs}$ system at high temperatures

The activity coefficients of the components of a $\mathrm{Na}$–$\mathrm{K}$–$\mathrm{Cs}$ ternary system in a temperature range of $773$–$1200$ K are determined using the previously calculated thermodynamic properties, in particular, the activity of the components of binary alloys of alkali metals such as $\mathrm{Na}$–$\mathrm{K}$, $\mathrm{Na}$–$\mathrm{Cs}$, and $\mathrm{K}$–$\mathrm{Cs}$, at high temperatures [1–3]. The sides of the triangle of the phase diagram of this system are constituted by the binary $\mathrm{Na}$–$\mathrm{K}$, $\mathrm{Na}$–$\mathrm{Cs}$, and $\mathrm{K}$–$\mathrm{Cs}$ binary alloys. The results obtained are used to calculate the saturated vapor pressure of the sodium–potassium-cesium eutectic ($22.1$ wt $\%\mathrm{K}$ and $73.8$ wt $\%\mathrm{Cs}$ [4, 5]) in the same temperature range. The calculated data are in good agreement with the recommended reference data [6].