Sodium aluminium hexafluoride is an
inorganic compound
In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...
with
formula
In science, a formula is a concise way of expressing information symbolically, as in a mathematical formula or a ''chemical formula''. The informal use of the term ''formula'' in science refers to the general construct of a relationship betwee ...
Na3 Al F6. This white solid, discovered in 1799 by Peder Christian Abildgaard (1740–1801), occurs naturally as the mineral
cryolite and is used extensively in the industrial production of aluminium metal. The compound is the sodium (Na
+) salt of the hexafluoroaluminate (AlF
63−) ion.
Production
Most cryolite is manufactured by a variety of related pathways. One route entails combining
sodium aluminate and
hydrofluoric acid
Hydrofluoric acid is a Solution (chemistry), solution of hydrogen fluoride (HF) in water. Solutions of HF are colourless, acidic and highly Corrosive substance, corrosive. It is used to make most fluorine-containing compounds; examples include th ...
:
:Na
3Al(OH)
6 + 6 HF → Na
3AlF
6 + 6 H
2O
Other routes include:
:
:
Often the
hexafluorosilicic acid, which is recovered from phosphate mining, is the precursor in a two-step process beginning with neutralization with ammonia to give
ammonium hexafluorosilicate:
:H
3AlF
6 + 3NH
3 → (NH
4)
3AlF
6
:(NH
4)
3AlF
6 + 3NaOH → Na
3AlF
6 + 3NH
3 + 3H
2O
The mineral form of sodium hexafluoroaluminate, which is called
cryolite, was mined at
Ivigtût on the west coast of Greenland until the deposit was depleted in 1987.
Use
The dominant application of synthetic
cryolite is as a
solvent (or
flux
Flux describes any effect that appears to pass or travel (whether it actually moves or not) through a surface or substance. Flux is a concept in applied mathematics and vector calculus which has many applications to physics. For transport ph ...
) for electrolysis of aluminium oxides such as
bauxite. The conversion of aluminium oxides into metallic aluminium requires that the metal ions be dissolved so that they can accept the electrons provided in the electrolysis cell. A mixture of cryolite and some
aluminium trifluoride is used as that solvent. Unlike typical solutions, this one requires temperatures approaching 1000 °C to melt. Other uses include a whitener for enamels and an opacifier for glass.
[
]
Structure
It adopts a perovskite-like structure. The centers are nearly idealized octahedra. Na+ occupy both six- and distorted 8-coordinate sites.
Safety
The is 600 mg/kg for the comparable compound aluminium trifluoride.[ Cryolite is poorly soluble in water.
]
Related compounds
* Chiolite ( ), another sodium fluoroaluminate.
References
External links
Chemical Land 21
{{fluorine compounds
Aluminium complexes
Fluoro complexes
Sodium compounds
Fluorometallates