Structural aspects of the formation of solid solutions in the NaF-KF-AlF3 system

Тип публикации: статья из журнала

Год издания: 2017

Идентификатор DOI: 10.1016/j.jssc.2017.04.037

Ключевые слова: Crystal structure refinement, NaF-KF-AlF3 system, Solid solution, X-ray powder diffraction, Crystal structure, Fluoride minerals, Metal ions, Ternary systems, Thermoanalysis, X ray diffraction, X ray powder diffraction, Crystal structure refinement, High temperature, Melting point temperature, NaF-KF-AlF<sub>3</sub> system, Polymorphic forms, Potassium ions, Sodium ions, Structural aspects, Solid solutions

Аннотация: The formation of solid solutions in the ternary system NaF-KF-AlF3 has been studied by X-ray diffraction and thermal analysis. Chiolite has been shown to form solid solutions with the composition (Na(5?x)Kx)Al3F14, in the limited range of 0<x<0.4. The lattice parameters change in the intervals for (a) 7.010 (3) ?7.050 (3) A, for (c) 10.365 (10) ?10.400 (10) A. According to the investigation of the crystal structure, potassium cations substitute sodium only in the 2-fold position in the amount of ~40%. The solid solutions are stable in the range from room to melting point temperature. A wide range of solid solutions based on ?-cryolite (Na3AlF6) and elpasolite (K2NaAlF6) above 540 °C has been studied in detail. It is only the 8-fold cationic position in the ?-cryolite structure which appears to have contributed into the substitution in the full range of solid solutions. The solid solution decays into a mixture of ?-Na3AlF6 and K2NaAlF6 upon calcination below 540 °C., followed by further cooling without changing the ?-Na3AlF6 composition. Elpasolitе initially containing an excess of sodium ions, has yielded cryolite and stoichiometric K2NaAlF6 below 340 °C. The phase K2NaAl3F12 present in two polymorphic forms, has not formed a wide range of solid solutions; however, a slight excess of potassium ions has improved the stability of the high-temperature form. © 2017 Elsevier Inc.

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Издание

Журнал: Journal of Solid State Chemistry

Выпуск журнала: Vol. 252

Номера страниц: 1-7

ISSN журнала: 00224596

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