Phase equilibria in a four-component system NaF–NaCl–Na₂MоO₄–Na₂WO₄

This paper presents a theoretical and experimental study of the four-component Na⁺||F^–,Cl^–,MoO₄^2–,WO₄^2– system. A stable triangle and a square divide systems into stable tetrahedron, five-vertex and six-vertex. The prediction of the number and composition of crystallizing phases carried out for stable elements of the phase tree. Faceting elements contain sodium molybdates and tungstates and compounds Na₃ClMoO₄, Na₃ClWO₄, Na₃FWO₄, Na₃FMoO₄, which form a continuous series of solid solutions – Na₂Mo_xW_1–xO₄, Na₃ClMo_xW_1–xO₄ and Na₄F₂Mo_xW_1–xO₄. A phase equilibria in the stable tetrahedron NaF–NaCl–D₃–D₄ experimentally studied by the method of differential thermal analysis. The absence of nonvariant equilibrium points in the tetrahedron and the stability of the continuous series of solid solutions established. The melting point and composition of the alloy maching to the point lying on the monovariant curve, connecting ternary eutectics E₂ and E₄ revealed. Phase reactions for various elements of the composition tetrahedron described.