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Calcium fluoride



Calcium fluoride
Identifiers
CAS number 7789-75-5
Properties
Molecular formula CaF2
Appearance White crystalline solid(single crystals are transparent)
Density 3.18 ×103 kg/m3 (solid)
Melting point

1402 °C, 1675 K, 2555 °F

Boiling point

2497 °C, 2770 K, 4526 °F

Solubility in water virtually insoluble
Hazards
Ingestion hazard low
Inhalation hazard low
Eye hazard low
Skin hazard low
Except where noted otherwise, data are given for
materials in their standard state
(at 25 °C, 100 kPa)

Infobox disclaimer and references

Calcium fluoride (CaF2) is an insoluble ionic compound of calcium and fluorine. It occurs naturally as the mineral fluorite (also called fluorspar), and it is the source of most of the world's fluorine. This insoluble solid adopts a cubic structure wherein calcium is coordinated to eight fluoride anions and each F ion is surrounded by four Ca2+ ions.[1] Although the pure material is colourless, the mineral is often deeply coloured due to the presence of F-centers.

Additional recommended knowledge

Contents

Source of HF

Naturally occurring CaF2 is the principal source of hydrogen fluoride, a commodity chemical used to produce a wide range of materials. Fluoride is liberated from the mineral by the action of concentrated sulfuric acid:

CaF2(s) + H2SO4(l) → CaSO4(solid) + 2 HF(g)

The resulting HF is converted into fluorine, fluorocarbons, and diverse fluoride materials. As of the late 1990s, five billion kilograms were mined annually.[2]

Other applications

Calcium fluoride is commonly used as a window material for both infrared and ultraviolet wavelengths, since it is transparent in these regions (about 0.15 µm to 9 µm) and exhibits extremely weak birefringence. Furthermore the material is fairly inert chemically so that these windows are not attacked. Nevertheless, at wavelengths as low as 157 nm, which are interesting to semiconductor manufacturers, the birefringence of calcium fluoride exceeds tolerable limits. This problem with birefringence can be mitigated through optimised growth process. It is particularly important as an ultraviolet optical material for integrated circuit lithography. Canon also uses artificially-crystallized calcium fluoride components in some of its L-series lenses to reduce light dispersion. As an infrared optical material, calcium fluoride is sometimes known by the Eastman Kodak trademarked name "Irtran-3," although this designation is obsolete.

Uranium-doped calcium fluoride was the second type of solid state laser invented, in the 1960s. Peter Sorokin and Mirek Stevenson at IBM's laboratories in Yorktown Heights (US) achieved lasing at 2.5 µm shortly after Maiman's ruby laser.

It is also used as a flux for melting and liquid processing of iron, steel and their composites. Its action is based on its similar melting point to iron, on its ability to dissolve oxides and on its ability to wet oxides and metals.

Safety

Fluorides are toxic to humans, however CaF2 is considered relatively harmless due to its extreme insolubility. The situation is analogous to BaSO4, where the toxicity normally associated with Ba2+ is offset by the very low solubility of its sulfate derivative.

References

  1. ^ G. L. Miessler and D. A. Tarr “Inorganic Chemistry” 3rd Ed, Pearson/Prentice Hall publisher, ISBN 0-13-035471-6.
  2. ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.

See also

Related materials

 
This article is licensed under the GNU Free Documentation License. It uses material from the Wikipedia article "Calcium_fluoride". A list of authors is available in Wikipedia.
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