Phase Equilibria in Four-Component System NaF–NaCl–Na2MоO4–Na2WO4

This paper presents a theoretical and experimental study of the four-component system NaF–NaCl–Na2MoO4–Na2WO4. A stable triangle and a square divide systems into stable tetrahedron, five-vertex, and six-vertex. The number and composition of crystallizing phases is predicted for stable elements of the phase tree. Faceting elements contain sodium molybdates and tungstates and compounds Na3ClMoO4, Na3ClWO4, Na3FWO4, and Na3FMoO4, which form a continuous series of solid solutions Na2MoxW1–xO4, Na3ClMoxW1‒xO4, and Na4F2MoxW1–xO4. A phase equilibria in the stable tetrahedron NaF–NaCl–D3–D4 has been 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 has been established. The melting point and composition of the alloy matching to the point lying on the monovariant curve and connecting ternary eutectics E2 and E4 have been revealed. Phase reactions are described for various elements of the tetrahedron of compositions of a four-component system.