| Aluminium fluoride | |
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Other names
Aluminium(III) fluoride |
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| Identifiers | |
| CAS number | 7784-18-1 , 32287-65-3 (monohydrate), 15098-87-0 (trihydrate) |
| PubChem | 2124 |
| ChemSpider | 2039 |
| ChEBI | CHEBI:49464 |
| RTECS number | BD0725000 |
| Jmol-3D images | Image 1 |
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| Properties | |
| Molecular formula | AlF3 |
| Molar mass | 83.9767 g/mol (anhydrous) 101.022 g/mol (monohydrate) 138.023 (trihydrate) |
| Appearance | white, crystalline solid odorless |
| Density | 2.88 g/cm (anhydrous) 2.1 g/cm3 (monohydrate) 1.914 g/cm3 (trihydrate) |
| Melting point |
1291 °C (anhydrous) |
| Solubility in water | 0.56 g/100 mL (0 °C) 0.67 g/100 mL (20 °C) 1.72 g/100 mL (100 °C) |
| Structure | |
| Crystal structure | Rhombohedral, hR24 |
| Space group | R-3c, No. 167 |
| Hazards | |
| EU classification | No classification according to EU Regulation (EC) No. 1272/2008. |
| R-phrases | - |
| S-phrases | - |
| NFPA 704 |
0
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| (verify) (what is: /?) Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa) |
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| Infobox references | |
Aluminium fluoride (AlF3) is an inorganic compound used primarily in the production of aluminium. This colourless solid can be prepared synthetically but also occurs in nature.
Contents |
The majority of aluminium fluoride is mainly produced by treating alumina with hexafluorosilicic acid:
Alternatively, it is manufactured by thermal decomposition of ammonium hexafluoroaluminate.[1] 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 AlF6 octahedra. Each fluoride is connected to two Al centers. Because of it is a 3-dimensional polymer, AlF3 has a higher melting point. In contrast, the other trihalides of aluminium, AlCl3, AlBr3, and AlI3, which are either molecular or 1-dimensional polymers, have low melting points and evaporate readily to give dimers.[2] In the gas phase, at ca. 1000 °C, 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 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.[1]
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.
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