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Chemical compound From Wikipedia, the free encyclopedia
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.
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3D model (JSmol) |
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ChEBI | |||
ChemSpider | |||
ECHA InfoCard | 100.029.262 | ||
EC Number |
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RTECS number |
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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) |
3.9 × 10−11 [1] | ||
Solubility | insoluble in acetone slightly soluble in acid | ||
-28.0·10−6 cm3/mol | |||
Refractive index (nD) |
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° | |||
Ca, 8, cubic F, 4, tetrahedral | |||
Hazards | |||
Occupational safety and health (OHS/OSH): | |||
Main hazards |
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) |
>5000 mg/kg (oral, guinea pig) 4250 mg/kg (oral, rat)[3] | ||
Safety data sheet (SDS) | ICSC 1323 | ||
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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The compound crystallizes in a cubic motif called the fluorite structure.
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.
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.
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]
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]
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]
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]
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