Calcium fluoride (CaF
2) is an insoluble
ionAn ion is an atom or molecule where the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge...
ic
compoundA chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
of
calciumCalcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft grey alkaline earth metal, and is the fifth most abundant element by mass in the Earth's crust...
and
fluorineFluorine is the chemical element with atomic number 9, represented by the symbol F. Fluorine forms a single bond with itself in elemental form, resulting in the diatomic F
2 molecule. F
2 is a supremely reactive, poisonous, pale, yellowish brown gas. Elemental fluorine is the...
. It occurs naturally as the mineral
fluoriteFluorite is a halide mineral composed of calcium fluoride, CaF
2. It is an isometric mineral with a cubic habit, though octahedral and more complex isometric forms are not uncommon. Cubic crystals up to 20 cm across have been found at Dalnegorsk, Russia...
(also called fluorspar) and as Blue John, and 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 Ca
2+ ions. Although the pure material is colourless, the mineral is often deeply coloured due to the presence of
F-centerAn F-Center is a type of crystallographic defect in which an anionic vacancy in a crystal is filled by one or more electrons, depending on the charge of the missing ion in the crystal. Electrons in such a vacancy tend to absorb light in the visible spectrum such that a material that is usually...
s.
Naturally occurring CaF
2 is the principal source of
hydrogen fluorideHydrogen fluoride is a chemical compound with the formula HF. It is the principal industrial source of fluorine, often in the aqueous form as hydrofluoric acid, and thus is the precursor to many important compounds including pharmaceuticals and polymers . HF is widely used in the petrochemical...
, a commodity chemical used to produce a wide range of materials.
Calcium fluoride (CaF
2) is an insoluble
ionAn ion is an atom or molecule where the total number of electrons is not equal to the total number of protons, giving it a net positive or negative electrical charge...
ic
compoundA chemical compound is a pure chemical substance consisting of two or more different chemical elements that can be separated into simpler substances by chemical reactions. Chemical compounds have a unique and defined chemical structure; they consist of a fixed ratio of atoms that are held together...
of
calciumCalcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft grey alkaline earth metal, and is the fifth most abundant element by mass in the Earth's crust...
and
fluorineFluorine is the chemical element with atomic number 9, represented by the symbol F. Fluorine forms a single bond with itself in elemental form, resulting in the diatomic F
2 molecule. F
2 is a supremely reactive, poisonous, pale, yellowish brown gas. Elemental fluorine is the...
. It occurs naturally as the mineral
fluoriteFluorite is a halide mineral composed of calcium fluoride, CaF
2. It is an isometric mineral with a cubic habit, though octahedral and more complex isometric forms are not uncommon. Cubic crystals up to 20 cm across have been found at Dalnegorsk, Russia...
(also called fluorspar) and as Blue John, and 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 Ca
2+ ions. Although the pure material is colourless, the mineral is often deeply coloured due to the presence of
F-centerAn F-Center is a type of crystallographic defect in which an anionic vacancy in a crystal is filled by one or more electrons, depending on the charge of the missing ion in the crystal. Electrons in such a vacancy tend to absorb light in the visible spectrum such that a material that is usually...
s.
Source of HF
Naturally occurring CaF
2 is the principal source of
hydrogen fluorideHydrogen fluoride is a chemical compound with the formula HF. It is the principal industrial source of fluorine, often in the aqueous form as hydrofluoric acid, and thus is the precursor to many important compounds including pharmaceuticals and polymers . HF is widely used in the petrochemical...
, a commodity chemical used to produce a wide range of materials. Fluoride is liberated from the mineral by the action of concentrated
sulfuric acidSulfuric acid, , is a strong mineral acid. It is soluble in water at all concentrations. Sulfuric acid has many applications, and is one of the top products of the chemical industry. World production in 2001 was 165 million tonnes, with an approximate value of US$8 billion...
:
- CaF2(s
Matter is generally found in three different forms: solid, liquid, and gas . The solid state of matter is characterized by a distinct structural rigidity and resistance to deformation . Most solids have high values both of Young's modulus and of the shear modulus of elasticity...
) + H2SO4(lLiquid is one of the principal states of matter. A liquid is a fluid that has the particles loose and can freely form a distinct surface at the boundaries of its bulk material. The surface is a free surface where the liquid is not constrained by a container....
) → CaSO4Calcium sulfate is a common laboratory and industrial chemical. In the form of γ-anhydrite , it is used as a desiccant. It is also used as a coagulant in products like tofu. In the natural state, unrefined calcium sulfate is a translucent, crystalline white rock...
(solid) + 2 HF(gThis page is about the physical properties of gas as a state of matter. For the uses of gases, and other meanings, see Gas .A gas is one of four states of matter. Near absolute zero, a substance exists as a solid...
)
The resulting HF is converted into fluorine,
fluorocarbonFluorocarbons, sometimes referred to as perfluorocarbons, are organofluorine compounds that contain only carbon and fluorine bonded together in strong carbon–fluorine bonds. Fluoroalkanes, that contain only single bonds, are more chemically and thermally stable than alkanes...
s, and diverse fluoride materials. As of the late 1990s, five billion kilograms were mined annually.
Other applications
Calcium fluoride is commonly used as a window material for both
infraredInfrared radiation is electromagnetic radiation whose wavelength is longer than that of visible light , but shorter than that of terahertz radiation and microwaves...
and
ultravioletUltraviolet light is electromagnetic radiation with a wavelength shorter than that of visible light, but longer than x-rays, in the range 10 nm to 400 nm, and energies from 3 eV to 124 eV...
wavelengths, since it is transparent in these regions (about 0.15 µm to 9 µm) and exhibits extremely low
refractive indexThe refractive index of a medium is a measure of how much the speed of light is reduced inside the medium. For example, typical soda-lime glass has a refractive index close to 1.5, which means that in glass, light travels at 1 / 1.5 = 2/3 the speed of light in a vacuum...
. Furthermore the material is fairly inert chemically so that these windows are not attacked. Nevertheless, at wavelengths as low as 157 nm, which are useful for
semiconductorA semiconductor is a material that has an electrical resistivity between that of a conductor and an insulator, that is, generally in the range 10
3 Siemens/cm to 10
−8 S/cm. Devices made from semiconductor materials are the foundation of modern electronics, including radio,...
manufacturers, the refractive index of calcium fluoride exceeds tolerable limits. This problem can be mitigated through optimised growth process. It is particularly important as an ultraviolet optical material for
integrated circuitIn electronics, an integrated circuit is a miniaturized electronic circuit that has been manufactured in the surface of a thin substrate of semiconductor material...
lithographyOptical lithography, is a process used in microfabrication to selectively remove parts of a thin film or the bulk of a substrate. It uses light to transfer a geometric pattern from a photo mask to a light-sensitive chemical photo resist, or simply "resist," on the substrate. A series of chemical...
.
Canonis a multinational corporation that specialises in the manufacture of imaging and optical products, including cameras, photocopiers, steppers and computer printers. Its headquarters are located in Ōta, Tokyo, Japan.-Company milestones:...
also uses artificially-crystallized calcium fluoride components in some of its
L-series lensesAn L lens is a line of SLR photography lenses made by Canon.L lenses are Canon's top-of-the-line lenses. The "L" officially stands for "Luxury", a reference to the lenses' high price and build quality. The use of "ASPH" was common to notate aspherical elements throughout Canon's and other...
to reduce
light dispersionIn optics, dispersion is the phenomenon in which the phase velocity of a wave depends on its frequency, or alternatively when the group velocity depends on the frequency.Media having such a property are termed dispersive media...
. As an infrared optical material, calcium fluoride is sometimes known by the
Eastman KodakEastman Kodak Company is a multinational US corporation which produces imaging and photographic materials and equipment. Long known for its wide range of photographic film products, Kodak is re-focusing on two major markets: digital photography and digital printing.- Origins :Kodak's origins rest...
trademarked name "Irtran-3," although this designation is obsolete.
UraniumUranium is a silvery-white metallic chemical element in the actinide series of the periodic table that has the symbol U and atomic number 92. Besides its 92 protons, a uranium nucleus can have between 141 and 146 neutrons. The most common uranium isotopes are U-238 and U-235 . A uranium atom has...
-
dopedIn semiconductor production, doping is the process of intentionally introducing impurities into an extremely pure semiconductor to change its electrical properties. The impurities are dependent upon the type of semiconductor. Lightly- and moderately-doped semiconductors are referred to as extrinsic...
calcium fluoride was the second type of solid state laser invented, in the 1960s. Peter Sorokin and Mirek Stevenson at
IBMInternational Business Machines Corporation, abbreviated IBM, is a multinational computer technology and IT consulting corporation headquartered in Armonk, Town of North Castle, New York, United States. The company is one of the few information technology companies with a continuous history dating...
's laboratories in Yorktown Heights (US) achieved lasing at 2.5 µm shortly after Maiman's
ruby laserA ruby laser is a solid-state laser that uses a synthetic ruby crystal as its gain medium. The first working laser was a ruby laser made by Theodore H. "Ted" Maiman at Hughes Research Laboratories on May 16, 1960....
.
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.
Safety
Fluorides are toxic to humans, however CaF
2 is considered relatively harmless due to its extreme insolubility. The situation is analogous to
BaSO4Barium sulfate is a white crystalline solid with the chemical formula BaSO4. It is insoluble in water and other traditional solvents but is soluble in concentrated sulfuric acid. The mineral barite is composed largely of barium sulfate and is a common ore of barium...
, where the toxicity normally associated with Ba
2+ is offset by the very low solubility of its sulfate derivative.
External links