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Aluminium fluoride

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Title: Aluminium fluoride  
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Subject: Aluminium monofluoride, Aluminium, Fluorides, Fluorophosphate glass, Fluorochemical industry
Collection: Aluminium Compounds, Fluorides, Metal Halides
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Aluminium fluoride

Aluminium fluoride
Aluminium trifluoride crystal structure
Names
Other names
Aluminium(III) fluoride
Aluminum trifluoride
Identifiers
 Y
(monohydrate) Y
(trihydrate) Y
ChEBI  Y
ChemSpider  Y
Jmol-3D images Image
PubChem
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)
Structure
Rhombohedral, hR24
R-3c, No. 167
Hazards
No classification according to EU Regulation (EC) No. 1272/2008.
R-phrases -
S-phrases -
NFPA 704
0
0
0
US health exposure limits (NIOSH):
PEL (Permissible)
none[1]
REL (Recommended)
2 mg/m3[1]
N.D.[1]
Except where otherwise noted, data are given for materials in their standard state (at 25 °C [77 °F], 100 kPa).
 Y  (: Y/N?)

Aluminium fluoride (AlF3) is an aluminium. This colorless solid can be prepared synthetically but also occurs in nature.

Contents

  • Production and occurrence 1
  • Structure 2
  • Applications 3
    • Niche uses 3.1
  • Safety 4
  • References 5
  • External links 6

Production and occurrence

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

H2SiF6 + Al2O3 → 2 AlF3 + SiO2 + H2O

Alternatively, it is manufactured by thermal decomposition of ammonium hexafluoroaluminate.[2] 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.

Structure

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.[3] Also they have low melting points and evaporate readily to give dimers.[4] 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.

Applications

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.[2]

Niche uses

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

It is also used to inhibit fermentation.

It is a sputtering target for preparation of low index films.

Safety

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

References

  1. ^ a b c "NIOSH Pocket Guide to Chemical Hazards #0024".  
  2. ^ a b J. Aigueperse, P. Mollard, D. Devilliers, M. Chemla, R. Faron, R. Romano, J. P. Cuer, "Fluorine Compounds, Inorganic" in Ullmann’s Encyclopedia of Industrial Chemistry, Wiley-VCH, Weinheim, 2005.doi:10.1002/14356007.a11_307
  3. ^  
  4. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.

External links

  • MSDS
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