Interaction in the system Li<sup>+</sup>,Na<sup>+</sup>,K<sup>+</sup>||F<sup>–</sup>Cl<sup>–</sup> and 3D model of a stable triangle LiF-NaCl-KCl

A 3D model of the phase equilibrium states of the quasi-ternary system LiF-NaCl-KCl, which is a stable triangle of a four-component reciprocal system Li+,Na+,K+||F–,Cl–, is constructed. Based on the 3D model, polythermal, isothermal sections and polytherms of phase crystallization were constructed for the first time. Two polythermal sections show the presence of areas of boundary solid solutions based on sodium and potassium chlorides. On the isothermal section at 620oC, the fields of coexisting phases are delimited. The crystallization polytherm is represented by three fields of crystallizing phases — lithium fluoride and boundary solid solutions based on NaCl and KCl. The stable character of the LiF-NaCl-KCl triangle is confirmed by thermodynamic calculation for several interaction temperatures of substances included in the unstable LiCl-NaF-KF triangle. The exothermic nature of the exchange reaction is confirmed by the exoeffect on the DTA curve of heating a mixture of powders of 50 mol.% LiCl+25 mol.% NaF+25 mol.% KF. The phases formed after the reaction — LiF, boundary solid solutions based on NaCl and KCl, are confirmed by X-ray phase analysis data. A low-melting region from the melting point of the ternary eutectic (604oC) to the isotherm (650oC) is isolated on the concentration triangle, mixtures of which can be used as a functional material for various purposes.