Aluminium fluoride

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Aluminium fluoride
Crystal structure
Other names
Aluminium(III) fluoride
Aluminum trifluoride
3D model (JSmol)
ECHA InfoCard 100.029.137
RTECS number BD0725000
Molar mass 83.977 g/mol (anhydrous)
101.992 g/mol (monohydrate)
138.023 (trihydrate)[1]
Appearance white, crystalline solid
Density 3.10 g/cm3 (anhydrous)
2.17 g/cm3 (monohydrate)
1.914 g/cm3 (trihydrate)[1]
Melting point 1,290 °C (2,350 °F; 1,560 K)[4] (anhydrous) (sublimes)
5.6 g/L (0 °C)
6.7 g/L (20 °C)
17.2 g/L (100 °C)
-13.4·10−6 cm3/mol[2]
1.3767 (visible range)[3]
Rhombohedral, hR24
R3c, No. 167[5]
a = 0.49254 nm, c = 1.24477 nm
75.1 J/mol·K[6]
66.5 J/mol·K[6]
−1510.4 kJ/mol[6]
-1431.1 kJ/mol[6]
No classification according to EU Regulation (EC) No. 1272/2008.
R-phrases (outdated)
S-phrases (outdated)
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)
REL (Recommended)
2 mg/m3[7]
IDLH (Immediate danger)
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
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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 as minerals rosenbergite and oskarssonite.

Production and occurrence[edit]

The majority of aluminium fluoride is produced by treating alumina with hydrogen fluoride gas at 700 °C:[4]

H2SiF6 + Al2O3 → 2 AlF3 + SiO2 + H2O

Alternatively, it is manufactured by thermal decomposition of ammonium hexafluoroaluminate.[8] 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. The non-hydrated form appears as the mineral oskarssonite.[9]


Its structure adopts the rhenium trioxide motif, featuring distorted AlF6 octahedra. 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.[10] Also they have low melting points and evaporate readily to give dimers.[11] 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.

Like most gaseous metal trifluorides, AlF3 adopts a planar structure upon evaporation.


Aluminium fluoride is an important additive for the production of aluminium by electrolysis.[4] 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.[8]

Niche uses[edit]

Together with zirconium fluoride, aluminium fluoride is an ingredient for the production of fluoroaluminate glasses.

It is also used to inhibit fermentation.

Like magnesium fluoride it used as a low-index optical thin film, particularly when far UV transparency is required. Its deposition by physical vapor deposition, particularly by evaporation, is favorable.


AlF3 has low toxicity (LD50 = 600 mg/kg).


  1. ^ a b Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, FL: CRC Press. p. 4.45. ISBN 1439855110. 
  2. ^ Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, FL: CRC Press. p. 4.131. ISBN 1439855110. 
  3. ^ Lide, David R. (2003-06-19). CRC Handbook of Chemistry and Physics, 84th Edition. CRC Handbook. CRC Press. ISBN 9780849304842. 
  4. ^ a b c Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. p. 233. ISBN 0-08-037941-9. 
  5. ^ Hoppe, R.; Kissel, D. (1984). "Zur kenntnis von AlF3 und InF3 [1]". Journal of Fluorine Chemistry. 24 (3): 327. doi:10.1016/S0022-1139(00)81321-4. 
  6. ^ a b c d Haynes, William M., ed. (2011). CRC Handbook of Chemistry and Physics (92nd ed.). Boca Raton, FL: CRC Press. p. 5.5. ISBN 1439855110. 
  7. ^ a b c "NIOSH Pocket Guide to Chemical Hazards #0024". National Institute for Occupational Safety and Health (NIOSH). 
  8. ^ a b Aigueperse, J.; Mollard, P.; Devilliers, D.; Chemla, M.; Faron, R.; Romano, R.; Cuer, J. P. (2005) "Fluorine Compounds, Inorganic" in Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim. doi:10.1002/14356007.a11_307
  9. ^ Oskarssonite. Mindat.
  10. ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 0-08-037941-9. 
  11. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.

External links[edit]