Calcium fluoride
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3D model (JSmol)
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| ECHA InfoCard | 100.029.262 | ||
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PubChem CID
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CompTox Dashboard (EPA)
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| 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) | |||
Solubility product (Ksp)
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3.9 × 10−11 [1] | ||
| Solubility | insoluble in acetone slightly soluble in acid | ||
| −28.0·10−6 cm3/mol | |||
Refractive index (nD)
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1.4338 | ||
| Structure | |||
| cubic crystal system, cF12[2] | |||
| Fm3m, #225 | |||
a = 5.451 Å, b = 5.451 Å, c = 5.451 Å α = 90°, β = 90°, γ = 90°
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| Ca, 8, cubic F, 4, tetrahedral | |||
| Hazards | |||
| Occupational safety and health (OHS/OSH): | |||
Main hazards
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Reacts with concentrated sulfuric acid to produce hydrofluoric acid | ||
| NFPA 704 (fire diamond) | |||
| Flash point | Non-flammable | ||
| Lethal dose or concentration (LD, LC): | |||
LDLo (lowest published)
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>5000 mg/kg (oral, guinea pig) 4250 mg/kg (oral, rat)[3] | ||
| Safety data sheet (SDS) | ICSC 1323 | ||
| Related compounds | |||
Other anions
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Calcium chloride Calcium bromide Calcium iodide | ||
Other cations
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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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Calcium fluoride is the inorganic compound of the elements calcium and fluorine with the formula CaF2. It is a white solid that is practically insoluble in water. It occurs as the mineral fluorite (also called fluorspar), which is often deeply coloured owing to impurities.
Chemical structure
[edit]The compound crystallizes in a cubic motif called the fluorite structure.
Ca2+ centres are eight-coordinate, being centred 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.
Gas phase
[edit]The gas phase is noteworthy for failing the predictions of VSEPR theory; the CaF2 molecule is not linear like MgF2, but bent with a bond angle of approximately 145°; the strontium and barium dihalides also have a bent geometry.[6] It has been proposed that this is due to the fluoride ligands interacting with the electron core[7][8] or the d-subshell[9] of the calcium atom.
Preparation
[edit]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:[10]
- CaCO3 + 2 HF → CaF2 + CO2 + H2O
Applications
[edit]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.[11] Hydrogen fluoride is liberated from the mineral by the action of concentrated sulfuric acid:[12]
- CaF2 + H2SO4 → CaSO4(solid) + 2 HF
Others
[edit]Calcium fluoride is used to manufacture optical components such as windows and lenses, used in thermal imaging systems, spectroscopy, telescopes, and excimer lasers (used for photolithography in the form of a fused lens). 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.[citation needed] It also allows much smaller wavelengths to pass through.[citation needed]
Doped calcium fluoride, like natural fluorite, exhibits thermoluminescence and is used in thermoluminescent dosimeters. It forms when fluorine combines with calcium.[citation needed]
Safety
[edit]CaF2 is classified as "not dangerous", although reacting it with sulfuric acid produces hydrofluoric acid, which is highly corrosive and toxic. With regards to inhalation, the NIOSH-recommended concentration of fluorine-containing dusts is 2.5 mg/m3 in air.[10]
See also
[edit]References
[edit]- ^ Pradyot Patnaik. Handbook of Inorganic Chemicals. McGraw-Hill, 2002, ISBN 0-07-049439-8.
- ^ 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.
- ^ "Fluorides (as F)". Immediately Dangerous to Life or Health Concentrations (IDLH). National Institute for Occupational Safety and Health (NIOSH).
- ^ 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. S2CID 119056949.
- ^ G. L. Miessler and D. A. Tarr "Inorganic Chemistry" 3rd Ed, Pearson/Prentice Hall publisher, ISBN 0-13-035471-6.
- ^ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN 978-0-08-037941-8.
- ^ Gillespie, R. J.; Robinson, E. A. (2005). "Models of molecular geometry". Chem. Soc. Rev. 34 (5): 396–407. doi:10.1039/b405359c. PMID 15852152.
- ^ Bytheway, I.; Gillespie, R. J.; Tang, T. H.; Bader, R.F (1995). "Core Distortions and Geometries of the Difluorides and Dihydrides of Ca, Sr, and Ba". Inorg. Chem. 34 (9): 2407–2414. doi:10.1021/ic00113a023.
- ^ Seijo, Luis; Barandiarán, Zoila; Huzinaga, Sigeru (1991). "Ab initio model potential study of the equilibrium geometry of alkaline earth dihalides: MX2 (M=Mg, Ca, Sr, Ba; X=F, Cl, Br, I)" (PDF). J. Chem. Phys. 94 (5): 3762. Bibcode:1991JChPh..94.3762S. doi:10.1063/1.459748. hdl:10486/7315.
- ^ a b 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. Weinheim: Wiley-VCH. doi:10.1002/14356007.a11_307. ISBN 3527306730.
- ^ 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.
- ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
External links
[edit]- NIST webbook thermochemistry data
- Charles Townes on the history of lasers
- National Pollutant Inventory - Fluoride and compounds fact sheet
- Crystran Material Data Archived 2012-11-10 at the Wayback Machine
- MSDS Archived 2011-11-21 at the Wayback Machine (University of Oxford)