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) | ||
| 0.0015 g/100 mL (18 °C) 0.0016 g/100 mL (20 °C) | |||
Solubility product (Ksp)
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3.9 x 10-11 [1] | ||
| Solubility | insoluble in acetone slightly soluble in acid | ||
Refractive index (nD)
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1.4338 | ||
| Structure | |||
| cubic crystal system, cF12[2] | |||
| Fm3m, #225 | |||
| Ca, 8, cubic F, 4, tetrahedral | |||
| Hazards | |||
| Occupational safety and health (OHS/OSH): | |||
Main hazards
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Reacts with conc. sulfuric acid to produce hydrofluoric acid | ||
| NFPA 704 (fire diamond) | |||
| Flash point | Non-flammable | ||
| Lethal dose or concentration (LD, LC): | |||
LD50 (median dose)
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4250 mg/kg (oral, rat) | ||
| 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 with the formula CaF2. This ionic compound of calcium and fluorine occurs naturally as the mineral fluorite (also called fluorspar). 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.[3] Although perfectly packed crystalline samples are colorless, the mineral is often deeply colored due to the presence of F-centers.
Chemical structure
Preparation
The mineral fluorspar is abundant, widespread, and mainly of interest as a precursor to HF. Thus, little motivation exists for the preparation of CaF2. High purity CaF2 is produced by treating calcium carbonate with hydrofluoric acid:[4]
- CaCO3 + 2 HF → CaF2 + CO2 + H2O
Source of HF
Naturally occurring CaF2 is the principal source of hydrogen fluoride, a commodity chemical used to produce a wide range of materials. Hydrogen fluoride is liberated from the mineral by the action of concentrated sulfuric acid:
The resulting HF is converted into fluorine, fluorocarbons, and diverse fluoride materials. As of the late 1990s, five billion kilograms were mined annually.[5]
Applications
In the laboratory, 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 low refractive index. Furthermore the material is attacked by few reagents. At wavelengths as short as 157 nm, a common wavelength used for semiconductor stepper manufacture for integrated circuit lithography, the refractive index of calcium fluoride shows some non-linearity at high power densities which has inhibited its use for this purpose. In the early years of the 21st century the stepper market for calcium fluoride collapsed and many large manufacturing facilities have been closed. Canon and other manufacturers have used synthetically grown crystals of calcium fluoride components in lenses to aid apochromatic design, and to reduce light dispersion. This use has largely been superseded by newer glasses and computer aided design. As an infrared optical material, calcium fluoride is widely available and was 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.
Calcium fluoride is one of the twelve Biochemic cell salts commonly used by homeopaths. In this context it is known by its Latin name, Calcarea Fluorata, typically abbreviated as "Calc Fluor." Like all homeopathic remedies, such a preparation of Calcium fluoride is highly diluted.
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
- ^ 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
- ^ G. L. Miessler and D. A. Tarr “Inorganic Chemistry” 3rd Ed, Pearson/Prentice Hall publisher, ISBN 0-13-035471-6.
- ^ Aigueperse, Jean (2005), "Fluorine Compounds, Inorganic", Ullmann's Encyclopedia of Industrial Chemistry, Weinheim: Wiley-VCH, doi:10.1002/14356007.a11_307
{{citation}}: Unknown parameter|coauthors=ignored (|author=suggested) (help) - ^ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN 0-12-352651-5.
See also
Related materials
External links
- NIST webbook thermochemistry data
- Uranium doped CaF2 laser (pdf file)
- Charles Townes on the history of lasers
- National Pollutant Inventory - Fluoride and compounds fact sheet
- Crystran Material Data
- MSDS (University of Oxford)