Calcium fluoride

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Calcium fluoride
Calcium fluoride.jpg
Fluorite-unit-cell-3D-ionic.png
Fluorid vapenaty.PNG
Identifiers
3D model (JSmol)
ChEBI
ChemSpider
ECHA InfoCard 100.029.262 OOjs UI icon edit-ltr-progressive.svg
EC Number
  • 232-188-7
PubChem CID
RTECS number
  • EW1760000
UNII
  • InChI=1S/Ca.2FH/h;2*1H/q+2;;/p-2 Yes check.svgY
    Key: WUKWITHWXAAZEY-UHFFFAOYSA-L Yes check.svgY
  • InChI=1/Ca.2FH/h;2*1H/q+2;;/p-2
    Key: WUKWITHWXAAZEY-NUQVWONBAZ
  • [Ca+2].[F-].[F-]
  • F[Ca]F
Properties
CaF2
Molar mass 78.075 g·mol−1
AppearanceWhite 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
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)
NFPA 704.svgHealth 0: Exposure under fire conditions would offer no hazard beyond that of ordinary combustible material. E.g. sodium chlorideFlammability 0: Will not burn. E.g. waterInstability 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]
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).
Yes check.svgY  verify  (what is  Yes check.svgYX mark.svgN ?)

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.

Contents

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. Xtals combined 2 300ppi.png
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.

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.

Gas phase

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

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

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

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

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

Related Research Articles

<span class="mw-page-title-main">Fluorite</span> Mineral form of calcium fluoride

Fluorite (also called fluorspar) is the mineral form of calcium fluoride, CaF2. It belongs to the halide minerals. It crystallizes in isometric cubic habit, although octahedral and more complex isometric forms are not uncommon.

<span class="mw-page-title-main">Hydrofluoric acid</span> Solution of hydrogen fluoride in water

Hydrofluoric acid is a solution of hydrogen fluoride (HF) in water. Solutions of HF are colorless, acidic and highly corrosive. It is used to make most fluorine-containing compounds; examples include the commonly used pharmaceutical antidepressant medication fluoxetine (Prozac) and the material PTFE (Teflon). Elemental fluorine is produced from it. It is commonly used to etch glass and silicon wafers.

<span class="mw-page-title-main">Tungsten hexafluoride</span> Chemical compound

Tungsten(VI) fluoride, also known as tungsten hexafluoride, is an inorganic compound with the formula WF6. It is a toxic, corrosive, colorless gas, with a density of about 13 kg/m3 (22 lb/cu yd). It is one of the densest known gases under standard conditions. WF6 is commonly used by the semiconductor industry to form tungsten films, through the process of chemical vapor deposition. This layer is used in a low-resistivity metallic "interconnect". It is one of seventeen known binary hexafluorides.

<span class="mw-page-title-main">Magnesium fluoride</span> Chemical compound of magnesium and fluorine

Magnesium fluoride is an ionically bonded inorganic compound with the formula MgF2. The compound is a white crystalline salt and is transparent over a wide range of wavelengths, with commercial uses in optics that are also used in space telescopes. It occurs naturally as the rare mineral sellaite.

<span class="mw-page-title-main">Sodium fluoride</span> Ionic compound (NaF)

Sodium fluoride (NaF) is an inorganic compound with the formula NaF. It is a colorless or white solid that is readily soluble in water. It is used in trace amounts in the fluoridation of drinking water to prevent tooth decay, and in toothpastes and topical pharmaceuticals for the same purpose. In 2020, it was the 265th most commonly prescribed medication in the United States, with more than 1 million prescriptions. It is also used in metallurgy and in medical imaging.

<span class="mw-page-title-main">Ammonium fluoride</span> Chemical compound

Ammonium fluoride is the inorganic compound with the formula NH4F. It crystallizes as small colourless prisms, having a sharp saline taste, and is highly soluble in water. Like all fluoride salts, it is moderately toxic in both acute and chronic overdose.

<span class="mw-page-title-main">FLiNaK</span>

FLiNaK is the name of the ternary eutectic alkaline metal fluoride salt mixture LiF-NaF-KF (46.5-11.5-42 mol %). It has a melting point of 454 °C and a boiling point of 1570 °C. It is used as electrolyte for the electroplating of refractory metals and compounds like titanium, tantalum, hafnium, zirconium and their borides. FLiNaK also could see potential use as a coolant in the very high temperature reactor, a type of nuclear reactor.

<span class="mw-page-title-main">Lithium fluoride</span> Chemical compound

Lithium fluoride is an inorganic compound with the chemical formula LiF. It is a colorless solid that transitions to white with decreasing crystal size. Although odorless, lithium fluoride has a bitter-saline taste. Its structure is analogous to that of sodium chloride, but it is much less soluble in water. It is mainly used as a component of molten salts. Partly because Li and F are both light elements, and partly because F2 is highly reactive, formation of LiF from the elements releases one of the highest energies per mass of reactants, second only to that of BeO.

<span class="mw-page-title-main">Iron(III) fluoride</span> Chemical compound

Iron(III) fluoride, also known as ferric fluoride, are inorganic compounds with the formula FeF3(H2O)x where x = 0 or 3. They are mainly of interest by researchers, unlike the related iron(III) chloride. Anhydrous iron(III) fluoride is white, whereas the hydrated forms are light pink.

<span class="mw-page-title-main">Hydrogen fluoride</span> Chemical compound

Hydrogen fluoride (fluorane) is an inorganic compound with chemical formula HF. It is a very poisonous, colorless gas or liquid that dissolves in water to yield an aqueous solution termed hydrofluoric acid. It is the principal industrial source of fluorine, often in the form of hydrofluoric acid, and is an important feedstock in the preparation of many important compounds including pharmaceuticals and polymers, e.g. polytetrafluoroethylene (PTFE). HF is also widely used in the petrochemical industry as a component of superacids. Due to strong and extensive hydrogen bonding, it boils at near room temperature, much higher than other hydrogen halides.

<span class="mw-page-title-main">Strontium fluoride</span> Chemical compound

Strontium fluoride, SrF2, also called strontium difluoride and strontium(II) fluoride, is a fluoride of strontium. It is a brittle white crystalline solid. In nature, it appears as the very rare mineral strontiofluorite.

<span class="mw-page-title-main">Hexafluorosilicic acid</span> Octahedric silicon compound

Hexafluorosilicic acid is an inorganic compound with the chemical formula H
2SiF
6. Aqueous solutions of hexafluorosilicic acid consist of salts of the cation and hexafluorosilicate anion. These salts and their aqueous solutions are colorless.

<span class="mw-page-title-main">Ammonium bifluoride</span> Chemical compound

Ammonium bifluoride is the inorganic compound with the formula [NH4][HF2] or [NH4]F·HF. It is produced from ammonia and hydrogen fluoride. This colourless salt is a glass-etchant and an intermediate in a once-contemplated route to hydrofluoric acid.

<span class="mw-page-title-main">Aluminium fluoride</span> Chemical compound

Aluminium fluoride is an inorganic compound with the formula AlF3. It forms hydrates AlF3·xH2O. Anhydrous AlF3 and its hydrates are all colorless solids. Anhydrous AlF3 is used in the production of aluminium metal. Several occur as minerals.

<span class="mw-page-title-main">Sodium hexafluoroaluminate</span> Chemical compound

Sodium hexafluoroaluminate is an inorganic compound with formula Na3AlF6. This white solid, discovered in 1799 by Peder Christian Abildgaard (1740–1801), occurs naturally as the mineral cryolite and is used extensively in the industrial production of aluminium metal. The compound is the sodium (Na+) salt of the hexafluoroaluminate (AlF63−) ion.

The bifluoride ion is an inorganic anion with the chemical formula [HF2]−. The anion is colorless. Salts of bifluoride are commonly encountered in the reactions of fluoride salts with hydrofluoric acid. The commercial production of fluorine involves electrolysis of bifluoride salts.

<span class="mw-page-title-main">Potassium bifluoride</span> Chemical compound

Potassium bifluoride is the inorganic compound with the formula K[HF2]. This colourless salt consists of the potassium cation and the bifluoride anion. The salt is used as an etchant for glass. Sodium bifluoride is related and is also of commercial use as an etchant as well as in cleaning products.

A monofluoride is a chemical compound with one fluoride per formula unit. For a binary compound, this is the formula XF.

<span class="mw-page-title-main">Fluorochemical industry</span> Industry dealing with chemicals from fluorine

The global market for chemicals from fluorine was about US$16 billion per year as of 2006. The industry was predicted to reach 2.6 million metric tons per year by 2015. The largest market is the United States. Western Europe is the second largest. Asia Pacific is the fastest growing region of production. China in particular has experienced significant growth as a fluorochemical market and is becoming a producer of them as well. Fluorite mining was estimated in 2003 to be a $550 million industry, extracting 4.5 million tons per year.

<span class="mw-page-title-main">Sodium bifluoride</span> Chemical compound

Sodium bifluoride is the inorganic compound with the formula Na[HF2]. It is a salt of sodium cation and bifluoride anion. It is a white, water-soluble solid that decomposes upon heating. Sodium bifluoride is non-flammable, hygroscopic, and has a pungent smell. Sodium bifluoride has a number of applications in industry.

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 or 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. S2CID   119056949.
  5. ↑ G. L. Miessler and D. A. Tarr "Inorganic Chemistry" 3rd Ed, Pearson/Prentice Hall publisher, ISBN   0-13-035471-6.
  6. ↑ Greenwood, Norman N.; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann. ISBN   978-0-08-037941-8.
  7. ↑ Gillespie, R. J.; Robinson, E. A. (2005). "Models of molecular geometry". Chem. Soc. Rev. 34 (5): 396–407. doi:10.1039/b405359c. PMID   15852152.
  8. ↑ 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.
  9. ↑ 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 .
  10. 1 2 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   978-3527306732.
  11. ↑ 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.
  12. ↑ Holleman, A. F.; Wiberg, E. "Inorganic Chemistry" Academic Press: San Diego, 2001. ISBN   0-12-352651-5.
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