Phase Complex of the Quinary Reciprocal System Li⁺,Na⁺,K⁺||F^–,Cl^–,Br^– and Investigation of the Stable Tetrahedron LiF–NaF–KCl–KBr

Abstract

The phase complex of the quinary reciprocal system Li⁺,Na⁺,K⁺||F^–,Cl^–,Br^– was studied for the first time. Partition according to graph theory determined that the tree of phases of the system has linear structure and comprises stable polytopes: the pentatope LiF–NaF–KF–KBr–KCl, the hexatope LiF–NaBr–NaCl–KCl–KBr–NaF, and the heptatope NaCl–KCl–KBr–LiBr–LiCl–LiF–NaBr, connected by the stable tetrahedron LiF–NaF–KCl–KBr and the stable pentatope LiF–KBr–NaBr–NaCl–KCl. Phase equilibria in the stable tetrahedron LiF–NaF–KCl–KBr were studied by differential thermal analysis and confirmed by X-ray powder diffraction analysis. In the tetrahedron, there is monovariant phase equilibrium L ⇄ LiF + α + KCl_xBr_{1 – x}, where α is a limited solid solution based on NaF (LiF–NaF system), and KCl_xBr_{1 – x} is a continuous series of solid solutions based on KCl and KBr. A 3D computer model of the projection of the phase complex on the concentration tetrahedron was constructed using the KOMPAS 3D software. The crystallization volumes of equilibrium phases are determined.