Thermal transformation of quaternary compounds in NaF-CaF{sub 2}-AlF{sub 3} system

Journal Article · Sat Aug 15 00:00:00 EDT 2009 · Journal of Solid State Chemistry

DOI:https://doi.org/10.1016/j.jssc.2009.05.043· OSTI ID:21370547

Zaitseva, Julia N ^[1]; Yakimov, Igor S ^[2]

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1. Institute of Chemistry and Chemical Technology SB RAS, K. Marx St., 42, Krasnoyarsk 660049 (Russian Federation)
2. Siberian Federal University, Svobodny Str., 79, Krasnoyarsk 660041 (Russian Federation)

Details of quaternary compounds formation in the system NaF-CaF{sub 2}-AlF{sub 3} are specified. To achieve this aim, the samples of phases NaCaAlF{sub 6} and Na{sub 2}Ca{sub 3}Al{sub 2}F{sub 14} have been obtained by high-temperature solid-phase synthesis. Their thermal behavior when heated up to 800 deg. C has been studied using the methods of high-temperature X-ray diffraction (XRD) and thermal analysis (TA). The system under consideration can be regarded as a quasibinary section CaF{sub 2}-NaAlF{sub 4}, where at T=745-750 deg. C invariant equilibrium is implemented with the phases CaF{sub 2}-NaCaAlF{sub 6}-Na{sub 2}Ca{sub 3}Al{sub 2}F{sub 14}-(liquid melt)-(NaAlF{sub 4}). The peculiarity of the equilibrium is NaAlF{sub 4} metastability at normal pressure. Below the equilibrium temperature the quaternary phase Na{sub 2}Ca{sub 3}Al{sub 2}F{sub 14} is stable and NaCaAlF{sub 6} above this temperature. The phase NaCaAlF{sub 6} fixed by rapid quenching from high temperatures and when heated up to 640 deg. C decomposes, yielding Na{sub 2}Ca{sub 3}Al{sub 2}F{sub 14}. Further heating in vacuum at temperature up to 740 deg. C results in decomposition of Na{sub 2}Ca{sub 3}Al{sub 2}F{sub 14} into CaF{sub 2} and Na{sub 3}AlF{sub 6}. The expected reverse transformation of Na{sub 2}Ca{sub 3}Al{sub 2}F{sub 14} into NaCaAlF{sub 6} has not been observed under experimental conditions. Transformations in bulk samples reveal direct and reverse transformation of quaternary phases. Synopsis: Thermal transformation of the quaternary compounds in system (NaF-CaF{sub 2}-AlF{sub 3}) was investigated using high-temperature X-ray diffraction (XRD) and thermal analysis (TA). In the system the invariant equilibrium is implemented with the phases CaF{sub 2}-NaCaAlF{sub 6}-Na{sub 2}Ca{sub 3}Al{sub 2}F{sub 14}-(liquid melt)-(NaAlF{sub 4}) at T=745-750 deg. C. - Graphical Abstract: The paper concerns of a small piece of the ternary system (NaF-CaF{sub 2}-AlF{sub 3}) which is very important for aluminum production. Details of phase relations were not fully understand up till now because of experimental difficulties: aggressive reagents and high temperature. However, the phase diagram is very important for production control.

• OSTI ID: 21370547
• Journal Information: Journal of Solid State Chemistry, Vol. 182, Issue 8; Other Information: DOI: 10.1016/j.jssc.2009.05.043; PII: S0022-4596(09)00248-5; 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
DECOMPOSITION
EQUILIBRIUM
HEATING
PHASE DIAGRAMS
QUENCHING
SODIUM FLUORIDES
SYNTHESIS
TEMPERATURE RANGE 0400-1000 K
TEMPERATURE RANGE 1000-4000 K
THERMAL ANALYSIS
X-RAY DIFFRACTION
ALKALI METAL COMPOUNDS
ALKALINE EARTH METAL COMPOUNDS
ALUMINIUM COMPOUNDS
CALCIUM COMPOUNDS
CALCIUM HALIDES
CHEMICAL REACTIONS
COHERENT SCATTERING
DIAGRAMS
DIFFRACTION
FLUORIDES
FLUORINE COMPOUNDS
HALIDES
HALOGEN COMPOUNDS
INFORMATION
SCATTERING
SODIUM COMPOUNDS
TEMPERATURE RANGE