Calcium fluoride

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Calcium fluoride
Calcium fluoride.jpg
Fluorite-unit-cell-3D-ionic.png
Fluorid vápenatý.PNG
Identifiers
7789-75-5 YesY
ChEBI CHEBI:35437 YesY
ChemSpider 23019 YesY
EC Number 232-188-7
Jmol 3D model Interactive image
PubChem 24617
RTECS number EW1760000
UNII O3B55K4YKI YesY
Properties
CaF2
Molar mass 78.07 g·mol−1
Appearance White crystalline solid (single crystals are transparent)
Density 3.18 g/cm3
Melting point 1,418 °C (2,584 °F; 1,691 K)
Boiling point 2,533 °C (4,591 °F; 2,806 K)
0.0015 g/100 mL (18 °C)
0.0016 g/100 mL (20 °C)
3.9 × 10−11 [1]
Solubility insoluble in acetone
slightly soluble in acid
1.4338
Structure
cubic crystal system, cF12[2]
Fm3m, #225
Ca, 8, cubic
F, 4, tetrahedral
Vapor pressure {{{value}}}
Related compounds
Other anions
Calcium chloride
Calcium bromide
Calcium iodide
Other cations
Beryllium fluoride
Magnesium fluoride
Strontium fluoride
Barium fluoride
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

Calcium fluoride is the inorganic compound with the formula CaF2. It is a colourless insoluble solid. It occurs as the mineral fluorite (also called fluorspar), which is often deeply coloured owing to impurities.

Chemical structure

The compound crystallizes in a cubic motif. Ca2+ centres are eight-coordinate, being centered in a "box" for eight F centres. Each F centre is coordinated to four Ca2+ centre.[3] Although perfectly packed crystalline samples are colorless, the mineral is often deeply colored due to the presence of F-centers.

The unit cell of CaF2 known as fluorite.

Preparation

The mineral fluorite is abundant, widespread, and mainly of interest as a precursor to HF. Thus, little motivation exists for the industrial production of CaF2. High purity CaF2 is produced by treating calcium carbonate with hydrofluoric acid:[4]

CaCO3 + 2 HF → CaF2 + CO2 + H2O

Applications

Main article: fluorite

Naturally occurring CaF2 is the principal source of hydrogen fluoride, a commodity chemical used to produce a wide range of materials. Calcium fluoride in the fluorite state is of significant commercial importance as a fluoride source.[5] Hydrogen fluoride is liberated from the mineral by the action of concentrated sulfuric acid:[6]

CaF2 + H2SO4CaSO4(solid) + 2 HF

Niche uses

Calcium fluoride is used to manufacture optical components such as windows and lenses, used in thermal imaging systems, spectroscopy, and excimer lasers. It is transparent over a broad range from ultraviolet (UV) to infrared (IR) frequencies. Its low refractive index eliminates the need for anti-reflection coatings. Its insolubility in water is convenient as well.

Safety

CaF2 is classified "not dangerous", although reacting it with sulphuric acid produces toxic hydrofluoric acid. With regards to inhalation, the NIOSH-recommended concentration of fluorine-containing dusts is 2.5 mg/m3 in air.[4]

References

  1. Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8
  2. X-ray Diffraction Investigations of CaF2 at High Pressure, L. Gerward, J. S. Olsen, S. Steenstrup, M. Malinowski, S. Åsbrink and A. Waskowska, Journal of Applied Crystallography (1992), 25, 578-581 doi:10.1107/S0021889892004096
  3. G. L. Miessler and D. A. Tarr “Inorganic Chemistry” 3rd Ed, Pearson/Prentice Hall publisher, ISBN 0-13-035471-6.
  4. 4.0 4.1 Aigueperse, Jean; Mollard, Paul; Devilliers, Didier; Chemla, Marius; Faron, Robert; Romano, René; Cuer, Jean Pierre (2000). "Fluorine Compounds, Inorganic". doi:10.1002/14356007.a11_307. 
  5. Aigueperse, Jean; Mollard, Paul; Devilliers, Didier; Chemla, Marius; Faron, Robert; Romano, Renée; Cuer, Jean Pierre (2005), "Fluorine Compounds, Inorganic", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, p. 307, doi:10.1002/14356007.a11_307.
  6. Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.

See also

Related materials

External links