PHASE EQUILIBRIA IN A THREE-COMPONENT RECIPROCAL SYSTEM Na, Sr∥F, MoO

This paper presents a theoretical and experimental study of the three-component reciprocal system Na, Sr∥F, MoO. A model for dividing the square of compositions into simplexes is presented and a variant with three phase triangles NaF–SrF–SrMoO, NaF–2NaF·NaMoO–SrMoO, 2NaF·NaMoO–SrMoO–NaMoO is confirmed by the thermodynamic method. The separation was experimentally confirmed by X-ray phase analysis of a mixture of 50 equi % NaMoO and 50 equi % SrF, corresponding to the point of complete conversion. A tree of phases was constructed and the main chemical reactions for mixtures corresponding to equivalence points were described. Using differential thermal analysis and thermogravimetry, a series of polythermal sections was studied, from which the directions to three points of invariant equilibria were determined. The coordinates of the eutectic and two peritectics have been revealed. All points of invariant equilibria are located in the phase triangle 2NaF·NaMoO–SrMoO–NaMoO. The phase complex of the system is represented by five crystallization fields — sodium and strontium fluorides, strontium molybdate, incongruent melting compounds and boundary solid solutions based on sodium molybdate. The minimum crystallization fields correspond to the compound 2NaF·NaMoO and the boundary solid solution based on sodium molybdate.