NaAlF{sub 4}: Preparation, crystal structure and thermal stability

Journal Article · Mon Feb 15 00:00:00 EST 2010 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2009.11.034· OSTI ID:21372501

Zaitseva, Julia N ^[1]

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1. Institute of Chemistry and Chemical Technology SB RAS, Karl Marks str., 42, Krasnoyarsk 660049 (Russian Federation)

The compound NaAlF{sub 4} has been obtained in the form of thin fibrous crystals or fine colorless powder by condensation at 18 deg. C of vapors arising over chiolite Na{sub 5}Al{sub 3}F{sub 14} or NaCaAlF{sub 6}, heated up to 800 deg. C. Thermal stability has been investigated by the methods of thermal analysis and high temperature X-ray diffraction. When heated in air, NaAlF{sub 4} is stable up to 390-400 deg. C, then there is an exothermal solid state decay into Na{sub 5}Al{sub 3}F{sub 14}(s) and AlF{sub 3}(s). At higher temperature Na{sub 5}Al{sub 3}F{sub 14}(s) decays into Na{sub 3}AlF{sub 6}(s) and NaAlF{sub 4}(g). The crystal structure (space group Cmcm, a=3.6124(1) A, b=14.9469(7) A, c=5.2617(3) A, V=284.10 A{sup 3}) has been determined by X-ray powder diffraction method. In the crystal structure of NaAlF{sub 4} the octahedrons [AlF{sub 6}] are joined through vertices and form corrugated layers, sodium ion layers being located between them. The distances between the atoms of Al-F are in the range 1.791-1.814 A, and those for Na...F are in the range 2.297-2.439 A. In spite of limited thermal stability of the crystal form, the compound NaAlF{sub 4} is the main component of the gas mixture over solid and molten salts in the ternary system NaF-AlF{sub 3}-CaF{sub 2} and participates in chemical transformations between the phases at high temperature. - Graphical abstract: The compound NaAlF{sub 4} was for the first time described 55 years ago, but until now it was not properly studied. Meantime the phase is responsible for the most low-melting part of the NaF-AlF{sub 3} system, which is the great importance for the aluminum production. The lack of information about NaAlF{sub 4} is due to narrow interval of stability which is close to liquid part of the system.

• OSTI ID: 21372501
• Journal Information: Journal of Solid State Chemistry, Vol. 183, Issue 2; Other Information: DOI: 10.1016/j.jssc.2009.11.034; PII: S0022-4596(09)00563-5; Copyright (c) 2009 Elsevier Science B.V., Amsterdam, The Netherlands, All rights reserved.; ISSN 0022-4596
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
37 INORGANIC
ORGANIC
PHYSICAL AND ANALYTICAL CHEMISTRY
ALUMINIUM FLUORIDES
CALCIUM FLUORIDES
MOLTEN SALTS
ORTHORHOMBIC LATTICES
PHASE DIAGRAMS
SODIUM FLUORIDES
SODIUM IONS
SPACE GROUPS
STABILITY
TEMPERATURE RANGE 0273-0400 K
TEMPERATURE RANGE 0400-1000 K
TEMPERATURE RANGE 1000-4000 K
THERMAL ANALYSIS
X RADIATION
X-RAY DIFFRACTION
ALKALI METAL COMPOUNDS
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
CALCIUM COMPOUNDS
CALCIUM HALIDES
CHARGED PARTICLES
COHERENT SCATTERING
CRYSTAL LATTICES
CRYSTAL STRUCTURE
DIAGRAMS
DIFFRACTION
ELECTROMAGNETIC RADIATION
FLUORIDES
FLUORINE COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
INFORMATION
IONIZING RADIATIONS
IONS
RADIATIONS
SALTS
SCATTERING
SODIUM COMPOUNDS
SYMMETRY GROUPS
TEMPERATURE RANGE