Phase Tree and Investigation of the NaBr-BaMoO4-BaWO4 Stable Triangle and the NaBr-BaBr2-BaMoO4-BaWO4 Stable Tetrahedron of the Na+,Ba2+||Br-, MoO4 -2 , WO4 -2 System

article presents a theoretical and experimental study of the stable elements of the Na+,Ba2+||Br-, MoO4 (- 2) , WO4 (- 2) , four-component reciprocal system. Simplex partitioning was performed based on graph theory. A phase tree with linear structure was built. The phase tree consists of a stable tetrahedron and a stable pentatope separated by a secant triangle. The numbers and compositions of crystallizing phases were predicted for the stable elements of the phase tree taking into account the boundary elements, which simultaneously contain isostructural sodium molybdate and tungstate together with barium molybdate and barium tungstate. After melting and crystallization, these compounds form a single phase of continuous solid solutions. The title system has been studied experimentally using DTA and X-ray powder diffraction. No invariant equilibrium points have been found in the stable elements of the system. The continuous sodium barium molybdate and tungstate solid solutions are stable. The melting points and compositions of the alloys at points on monovariant equilibrium curves have been determined.