Calcium fluoride

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

Calcium fluoride
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.029.262
EC Number
  • 232-188-7
RTECS number
  • EW1760000
UNII
Properties
CaF2
Molar mass 78.075 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)
0.015 g/L (18 °C)
0.016 g/L (20 °C)
3.9 × 10−11 [1]
Solubility insoluble in acetone
slightly soluble in acid
-28.0·10−6 cm3/mol
1.4338
Structure
cubic crystal system, cF12[2]
Fm3m, #225
Ca, 8, cubic
F, 4, tetrahedral
Hazards
Main hazards Reacts with concentrated sulfuric acid to produce hydrofluoric acid
Safety data sheet ICSC 1323
NFPA 704 (fire diamond)
Flammability code 0: Will not burn. E.g. waterHealth code 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g. sodium chlorideReactivity code 0: Normally stable, even under fire exposure conditions, and is not reactive with water. E.g. liquid nitrogenSpecial hazards (white): no code
0
0
0
Flash point Non-flammable
Lethal dose or concentration (LD, LC):
>5000 mg/kg (oral, guinea pig)
4250 mg/kg (oral, rat)[3]
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

Chemical structure

The compound crystallizes in a cubic motif called the fluorite structure.

Unit cell of CaF2, known as fluorite structure, from two equivalent perspectives. The second origin is often used when visualising point defects entered on the cation.[4]

Ca2+ centres are eight-coordinate, being centered in a cube of eight F− centres. Each F− centre is coordinated to four Ca2+ centres in the shape of a tetrahedron.[5] Although perfectly packed crystalline samples are colorless, the mineral is often deeply colored due to the presence of F-centers. The same crystal structure is found in numerous ionic compounds with formula AB2, such as CeO2, cubic ZrO2, UO2, ThO2, and PuO2. In the corresponding anti-structure, called the antifluorite structure, anions and cations are swapped, such as Be2C.

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:[6]

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.[7] Hydrogen fluoride is liberated from the mineral by the action of concentrated sulfuric acid:[8]

CaF2 + H2SO4 → CaSO4(solid) + 2 HF

Niche uses

Calcium fluoride is used to manufacture optical components such as windows and lenses, used in thermal imaging systems, spectroscopy, telescopes, and excimer lasers. It is transparent over a broad range from ultraviolet (UV) to infrared (IR) frequencies. Its low refractive index reduces the need for anti-reflection coatings. Its insolubility in water is convenient as well. Doped calcium fluoride, like natural fluorite, exhibits thermoluminescence and is used in thermoluminescent dosimeters. It forms when fluorine combines with calcium.

Safety

CaF2 is classified as "not dangerous", although reacting it with sulfuric acid produces very toxic hydrofluoric acid. With regards to inhalation, the NIOSH-recommended concentration of fluorine-containing dusts is 2.5 mg/m3 in air.[6]

gollark: No, however there is the FSG.
gollark: I don't live there. I live in Antarctica.
gollark: Gnobody: experiencing planning fallacy.
gollark: > trivial
gollark: <@319753218592866315> Coltrans exists. Lyricly make macron.

See also

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. "Fluorides (as F)". Immediately Dangerous to Life and Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
  4. Burr, P. A.; Cooper, M. W. D. (2017-09-15). "Importance of elastic finite-size effects: Neutral defects in ionic compounds". Physical Review B. 96 (9): 094107. arXiv:1709.02037. Bibcode:2017PhRvB..96i4107B. doi:10.1103/PhysRevB.96.094107.
  5. G. L. Miessler and D. A. Tarr “Inorganic Chemistry” 3rd Ed, Pearson/Prentice Hall publisher, ISBN 0-13-035471-6.
  6. Aigueperse, Jean; Mollard, Paul; Devilliers, Didier; Chemla, Marius; Faron, Robert; Romano, René; Cuer, Jean Pierre (2000). "Fluorine Compounds, Inorganic". Ullmann's Encyclopedia of Industrial Chemistry. doi:10.1002/14356007.a11_307. ISBN 3527306730.
  7. 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.
  8. Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
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