Abstract
The fusibility of salt mixtures in the anhydrous quadruple AlF3-KF-NaF-ZrF4 system was studied. The direction of lowering the melting point of substances in the tetrahedron of the composition of the quadruple system, the influence of complexation on lowering the melting point of salt mixtures, were clarified.
 The fusibility of salts in the ternary AlF3-NaF-ZrF4 system was investigated experimentally by methods of thermal phase analysis. The diagram of fusibility to the isotherm of 900 °C is constructed. Primary crystallization fields are represented by the phases of the initial salts (AlF3, KF, ZrF4) of the compounds that were formed in binary subsystems (2KF∙ZrF4, 7NaF∙6ZrF4, 3NaF∙4ZrF4, 5NaF∙3AlF3) and Na3AlF6-Na3ZrF7 solid solutions. The minimum melting point was 466 ° C in a triple eutectic.
 The fusibility of salt mixtures was experimentally studied in the subsystem K2ZrF6-Na2ZrF6-KAlF4-NaAlF4, which was a section of the tetrahedron of the composition of the quadruple system AlF3-KF-NaF-ZrF4. The fusibility diagram of this subsystem was constructed. A triple point with a melting point of 450 °C was found. Primary crystallization fields are represented by compounds K2ZrF6, Na2ZrF6 and solid solutions KAlF4-NaAlF4.
 The low-melting region of the compositions in the tetrahedron of the composition of the quadruple system was shifted to the faces NaF-KF-ZrF4 and AlF3-KF-ZrF4. The intense chemical interaction of the starting materials of the quadruple system with the formation of complex compounds and the extensive formation of solid solutions complicated the determination of crystallizing solid phases and the establishment of monovariant equilibria in quadruple mixtures.
 Quadruple eutectic in the four component system was formed by the merger of four monovariant lines. To calculate the composition of the quadruple eutectic by the melting temperature and the composition of the eutectic of the triple subsystems, the coordinates of the four triple points are necessary. The characteristic of two triple points was obtained as a result of an experimental study of the fusibility diagrams of auxiliary sections of a tetrahedron of the composition: K2ZrF4-Na2ZrF6-KAlF4-NaAlF4 and KZrF6-NaAlF4-(0,5NaF+0,5ZrF4)-KAlF4, which were located near the quadruple eutectic.
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