Thermodynamic assessments of six binary systems of alkali metals

Among the phase diagrams of six binary systems composed of alkali metals, Sodium (Na), Potassium (K), Rubidium (Rb) and Cesium (Cs), three of them, those of the Cs–K, Cs–Rb and K–Rb systems, indicate a complete range of solid solubility, and the other three, those of the Cs–Na, K–Na and Na–Rb systems, have the eutectic type characteristic. The computational thermodynamic descriptions of the six binary systems were modeled by the CALPHAD technique. The solution phases, liquid and body-centered cubic, were described using a substitution model, with the excess Gibbs energies formulated by the Redlich–Kister expression. The intermediate phases with no solubility ranges, KNa2 and CsNa2, were treated as stoichiometric compounds. The thermodynamic properties and the phase diagrams of the six binary systems were predicted. The consistency between the calculated results and the reported experimental measurements for the phase equilibria and the thermochemical properties has been obtained for all of the six binary systems.