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Aluminium fluoride

Aluminium fluoride
Aluminium trifluoride crystal structure
FeF3structure.jpg
Names
Other names
Aluminium(III) fluoride
Aluminum trifluoride
Identifiers
7784-18-1 YesY
32287-65-3 (monohydrate) YesY
15098-87-0 (trihydrate) YesY
3D model (Jmol) Interactive image
ChEBI CHEBI:49464 YesY
ChemSpider 2039 YesY
ECHA InfoCard 100.029.137
PubChem 2124
RTECS number BD0725000
Properties
AlF3
Molar mass 83.9767 g/mol (anhydrous)
101.022 g/mol (monohydrate)
138.023 (trihydrate)
Appearance white, crystalline solid
odorless
Density 3.1 g/cm3 (anhydrous)
2.1 g/cm3 (monohydrate)
1.914 g/cm3 (trihydrate)
Melting point 1,291 °C (2,356 °F; 1,564 K) (anhydrous) (sublimes)
0.56 g/100 mL (0 °C)
0.67 g/100 mL (20 °C)
1.72 g/100 mL (100 °C)
-13.4·10−6 cm3/mol
1.3767 (visible range)
Structure
Rhombohedral, hR24
R-3c, No. 167
Hazards
No classification according to EU Regulation (EC) No. 1272/2008.
R-phrases -
S-phrases -
NFPA 704
Flammability code 0: Will not burn. E.g., water Health code 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g., sodium chloride Reactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g., liquid nitrogen Special hazards (white): no codeNFPA 704 four-colored diamond
US health exposure limits (NIOSH):
PEL (Permissible)
 none
REL (Recommended)
 2 mg/m3
IDLH (Immediate danger)
 N.D.
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
YesY  (what is YesYN ?)
Infobox references

Aluminium fluoride (AlF3) is an inorganic compound used primarily in the production of aluminium. This colorless solid can be prepared synthetically but also occurs in nature.

The majority of aluminium fluoride is produced by treating alumina with hexafluorosilicic acid:

Alternatively, it is manufactured by thermal decomposition of ammonium hexafluoroaluminate. For small scale laboratory preparations, AlF3 can also be prepared by treating aluminium hydroxide or aluminium metal with HF.

Aluminium fluoride trihydrate is found in nature as the rare mineral rosenbergite.

Its structure adopts the rhenium trioxide motif, featuring distorted AlF6octahedra. Each fluoride is connected to two Al centers. Because of its 3-dimensional polymeric structure, AlF3 has a high melting point. The other trihalides of aluminium in the solid state differ, AlCl3 has a layer structure and AlBr3 and AlI3, are molecular dimers. Also they have low melting points and evaporate readily to give dimers. In the gas phase aluminium fluoride exists as trigonal molecules of D3h symmetry. The Al-F bond lengths of this gaseous molecule are 163 pm.

Aluminium fluoride is an important additive for the production of aluminium by electrolysis. Together with cryolite, it lowers the melting point to below 1000 °C and increases the conductivity of the solution. It is into this molten salt that aluminium oxide is dissolved and then electrolyzed to give bulk Al metal.


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