Aluminum fluoride

Crystal structure
__ Al 3+      __ F -
General
Surname	Aluminum fluoride
other names	Aluminum trifluoride Aluminum (III) trifluoride
Ratio formula	AlF 3
Brief description	colorless hexagonal crystals
External identifiers / databases
CAS number 7784-18-1 32287-65-3 (monohydrate) 15098-87-0 (trihydrate) PubChem 2124 Wikidata Q409057
properties
Molar mass	83.98 g mol −1
Physical state	firmly
density	2.88 g cm −3
Sublimation point	approx. 1260 ° C
solubility	poorly soluble in water, acids and alkalis
safety instructions
GHS labeling of hazardous substances Caution H and P phrases H: 302-315-319-335 P: 261-305 + 351 + 338
MAK	1 mg m −3 (measured as the inhalable aerosol fraction)
Thermodynamic properties
ΔH f 0	−1510.4 (13) kJ / mol
As far as possible and customary, SI units are used. Unless otherwise noted, the data given apply to standard conditions .

Aluminum fluoride is a salt of aluminum and fluorine with the empirical formula AlF ₃ .

Occurrence

Aluminum fluoride occurs both anhydrous and in several forms containing water of crystallization .

synthesis

Aluminum fluoride is expediently prepared by passing hydrogen fluoride over red-hot aluminum oxide :

${\displaystyle \mathrm {Al_{2}O_{3}+6\ HF\rightarrow 2\ AlF_{3}+3\ H_{2}O} }$

A possible dehydration of the trihydrate (AlF ₃ · 3 H ₂ O) obtainable from aqueous solution is never entirely free from the production of a hydrolysis product containing oxide (Al ₂ O ₃ ) or oxyfluoride (AlOF). In order to produce pure anhydrous aluminum fluoride, one falls back on the decomposition of ammonium hexafluoroaluminate :

${\displaystyle \mathrm {(NH_{4})_{3}AlF_{6}\rightarrow AlF_{3}+3\ NH_{4}F} }$

properties

Aluminum fluoride forms a colorless trigonal crystal powder with the space group R 3 (space group no. 148) and the lattice parameters a = 4.9254 Å , c = 12.4477 Å, which is sparingly soluble in water and organic solvents .

Responsiveness

With fluorides of the alkali metals , complex salts of the compositions M (AlF ₄ ), M ₂ (AlF ₅ ) and M ₃ (AlF ₆ ) are formed. Cryolite Na ₃ [AlF ₆ ] is of technical importance here .

use

Aluminum fluoride is used as a catalyst as well as in dental care for caries prophylaxis . In its pure form as well as cryolite , it is used as a flux for melting light metals and for producing aluminum. In this way, the melting temperature of aluminum oxide can be reduced from approx. 2000 ° C to 1000 ° C.

Individual evidence

1. ↑ ^{a b c} Entry on aluminum fluoride. In: Römpp Online . Georg Thieme Verlag, accessed on December 25, 2014.
2. ↑ ^{a b c d} Entry on aluminum fluoride in the GESTIS material database of the IFA , accessed on December 23, 2007(JavaScript required) .
3. ↑ ^{a b} Data sheet Aluminum fluoride from Sigma-Aldrich , accessed on March 20, 2011 ( PDF ).
4. ↑ David R. Lide (Ed.): CRC Handbook of Chemistry and Physics . 90th edition. (Internet version: 2010), CRC Press / Taylor and Francis, Boca Raton, FL, CODATA Key Values ​​for Thermodynamics, pp. 5-1.
5. ↑ G. Brauer (Ed.), Handbook of Preparative Inorganic Chemistry 2nd ed., Vol. 1, Academic Press 1963, pp. 225-226.
6. ↑ R. Hoppe, D. Kissel: On the knowledge of AlF ₃ and InF ₃ . In: Journal of Fluorine Chemistry , 1984 , 24 , pp. 327-340 doi : 10.1016 / S0022-1139 (00) 81321-4