Lithium fluoride is an

inorganic compound In chemistry, an inorganic compound is typically a chemical compound that lacks carbon–hydrogen bonds, that is, a compound that is not an organic compound. The study of inorganic compounds is a subfield of chemistry known as '' inorganic chemist ...

with the

chemical formula In chemistry, a chemical formula is a way of presenting information about the chemical proportions of atoms that constitute a particular chemical compound or molecule, using chemical element symbols, numbers, and sometimes also other symbols, ...

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 Sodium chloride , commonly known as salt (although sea salt also contains other chemical salts), is an ionic compound with the chemical formula NaCl, representing a 1:1 ratio of sodium and chloride ions. With molar masses of 22.99 and 35.45 g ...

, but it is much less soluble in water. It is mainly used as a component of

molten salt Molten salt is salt which is solid at standard temperature and pressure but enters the liquid phase due to elevated temperature. Regular table salt has a melting point of 801 °C (1474°F) and a heat of fusion of 520 J/g.< ...

s. Formation of LiF from the elements releases one of the highest energy per mass of reactants, second only to that of

BeO BEO, Beo, BeO or ''variation'' may refer to: ;BEO * Banquet event order * Belmont Airport IATA code * Book entry only * Beyond Earth Orbit ;Beo * ''Beo'', a variant of the name of the Anglo-Saxon god Beowa. * Beo language, an African language ...

Manufacturing

LiF is prepared from

lithium hydroxide Lithium hydroxide is an inorganic compound with the formula LiOH. It can exist as anhydrous or hydrated, and both forms are white hygroscopic solids. They are soluble in water and slightly soluble in ethanol. Both are available commercially. While ...

lithium carbonate Lithium carbonate is an inorganic compound, the lithium salt (chemistry), salt of carbonate with the chemical formula, formula . This white Salt (chemistry), salt is widely used in the processing of metal oxides. It is listed on the World Health O ...

with

hydrogen fluoride Hydrogen fluoride (fluorane) is an inorganic compound with the chemical formula . This colorless gas or liquid is the principal industrial source of fluorine, often as an aqueous solution called hydrofluoric acid. It is an important feedstock i ...

Applications

Precursor to LiPF₆ for batteries

Lithium fluoride is reacted with

(HF) and

phosphorus pentachloride Phosphorus pentachloride is the chemical compound with the formula PCl5. It is one of the most important phosphorus chlorides, others being PCl3 and POCl3. PCl5 finds use as a chlorinating reagent. It is a colourless, water-sensitive and moist ...

to make

lithium hexafluorophosphate Lithium hexafluorophosphate is an inorganic compound with the formula Li PF6. It is a white crystalline powder. Production LiPF6 is manufactured by reacting phosphorus pentachloride with hydrogen fluoride and lithium fluoride :PCl5 + LiF + 5 ...

, an ingredient in

lithium ion battery A lithium-ion or Li-ion battery is a type of rechargeable battery which uses the reversible reduction of lithium ions to store energy. It is the predominant battery type used in portable consumer electronics and electric vehicles. It also se ...

electrolyte An electrolyte is a medium containing ions that is electrically conducting through the movement of those ions, but not conducting electrons. This includes most soluble salts, acids, and bases dissolved in a polar solvent, such as water. Upon dis ...

In molten salts

Fluorine is produced by the

electrolysis In chemistry and manufacturing, electrolysis is a technique that uses direct electric current (DC) to drive an otherwise non-spontaneous chemical reaction. Electrolysis is commercially important as a stage in the separation of elements from n ...

of molten

potassium bifluoride Potassium bifluoride is the inorganic compound with the formula . 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 commercia ...

. This electrolysis proceeds more efficiently when the electrolyte contains a few percent of LiF, possibly because it facilitates formation of an Li-C-F interface on the carbon

electrode An electrode is an electrical conductor used to make contact with a nonmetallic part of a circuit (e.g. a semiconductor, an electrolyte, a vacuum or air). Electrodes are essential parts of batteries that can consist of a variety of materials de ...

s. A useful molten salt,

FLiNaK 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 ...

, consists of a mixture of LiF, together with

sodium fluoride Sodium fluoride (NaF) is an inorganic compound with the formula . It is used in trace amounts in the fluoridation of drinking water, in toothpaste, in metallurgy, and as a flux. It is a colorless or white solid that is readily soluble in water. I ...

and

potassium fluoride Potassium fluoride is the chemical compound with the formula KF. After hydrogen fluoride, KF is the primary source of the fluoride ion for applications in manufacturing and in chemistry. It is an alkali halide and occurs naturally as the rare m ...

. The primary coolant for the

Molten-Salt Reactor Experiment The Molten-Salt Reactor Experiment (MSRE) was an experimental molten salt reactor research reactor at the Oak Ridge National Laboratory (ORNL). This technology was researched through the 1960s, the reactor was constructed by 1964, it went critica ...

was

FLiBe FLiBe is a molten salt made from a mixture of lithium fluoride (LiF) and beryllium fluoride (BeF2). It is both a nuclear reactor coolant and solvent for fertile or fissile material. It served both purposes in the Molten-Salt Reactor Experiment ...

; LiF-BeF₂ (66-33 mol%).

Optics

Because of the large

band gap In solid-state physics, a band gap, also called an energy gap, is an energy range in a solid where no electronic states can exist. In graphs of the electronic band structure of solids, the band gap generally refers to the energy difference (in ...

for LiF, its crystals are

transparent Transparency, transparence or transparent most often refer to: * Transparency (optics), the physical property of allowing the transmission of light through a material They may also refer to: Literal uses * Transparency (photography), a still, ...

to short wavelength

ultraviolet Ultraviolet (UV) is a form of electromagnetic radiation with wavelength from 10 nanometer, nm (with a corresponding frequency around 30 Hertz, PHz) to 400 nm (750 Hertz, THz), shorter than that of visible light, but longer than ...

radiation In physics, radiation is the emission or transmission of energy in the form of waves or particles through space or through a material medium. This includes: * ''electromagnetic radiation'', such as radio waves, microwaves, infrared, visi ...

, more so than any other

material Material is a substance or mixture of substances that constitutes an object. Materials can be pure or impure, living or non-living matter. Materials can be classified on the basis of their physical and chemical properties, or on their geologi ...

. LiF is therefore used in specialized

optics Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it. Optics usually describes the behaviour of visible, ultraviole ...

for the vacuum ultraviolet spectrum, (See also

magnesium fluoride Magnesium fluoride is an 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 natur ...

). Lithium fluoride is used also as a diffracting crystal in X-ray spectrometry.

Radiation detectors

It is also used as a means to record

ionizing radiation Ionizing radiation (or ionising radiation), including nuclear radiation, consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from them. Some particles can travel ...

exposure from

gamma rays A gamma ray, also known as gamma radiation (symbol γ or \gamma), is a penetrating form of electromagnetic radiation arising from the radioactive decay of atomic nuclei. It consists of the shortest wavelength electromagnetic waves, typically ...

beta particles A beta particle, also called beta ray or beta radiation (symbol β), is a high-energy, high-speed electron or positron emitted by the radioactive decay of an atomic nucleus during the process of beta decay. There are two forms of beta decay, β� ...

, and

neutrons The neutron is a subatomic particle, symbol or , which has a neutral (not positive or negative) charge, and a mass slightly greater than that of a proton. Protons and neutrons constitute the nuclei of atoms. Since protons and neutrons behave ...

(indirectly, using the (n,alpha)

nuclear reaction In nuclear physics and nuclear chemistry, a nuclear reaction is a process in which two atomic nucleus, nuclei, or a nucleus and an external subatomic particle, collide to produce one or more new nuclides. Thus, a nuclear reaction must cause a t ...

) in

thermoluminescent dosimeter A thermoluminescent dosimeter, or TLD, is a type of radiation dosimeter, consisting of a piece of a thermoluminescent crystalline material inside a radiolucent package. When a thermoluminescent crystal is exposed to ionizing radiation, it abso ...

s. ⁶LiF nanopowder enriched to 96% has been used as the neutron reactive backfill material for microstructured semiconductor neutron detectors (MSND).

Nuclear reactors

Lithium fluoride (highly enriched in the common isotope lithium-7) forms the basic constituent of the preferred fluoride salt mixture used in liquid-fluoride nuclear reactors. Typically lithium fluoride is mixed with

beryllium fluoride Beryllium fluoride is the inorganic compound with the chemical formula, formula Beryllium, BeFluorine, F2. This white solid is the principal precursor for the manufacture of beryllium metal. Its structure resembles that of quartz, but BeF2 is hig ...

to form a base solvent (

), into which fluorides of uranium and thorium are introduced. Lithium fluoride is exceptionally chemically stable and LiF/BeF₂ mixtures (

) have low melting points () and the best neutronic properties of fluoride salt combinations appropriate for reactor use. MSRE used two different mixtures in the two cooling circuits.

Cathode for PLED and OLEDs

Lithium fluoride is widely used in

PLED An organic light-emitting diode (OLED or organic LED), also known as organic electroluminescent (organic EL) diode, is a light-emitting diode (LED) in which the emissive electroluminescent layer is a film of organic compound that emits light i ...

and

OLED An organic light-emitting diode (OLED or organic LED), also known as organic electroluminescent (organic EL) diode, is a light-emitting diode (LED) in which the emissive electroluminescent layer is a film of organic compound that emits light i ...

as a coupling layer to enhance electron injection. The thickness of the LiF layer is usually around 1 nm. The dielectric constant (or relative permittivity) of LiF is 9.0.

Natural occurrence

Naturally occurring lithium fluoride is known as the extremely rare mineral

griceite 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 ...

References

{{Authority control Lithium compounds Fluorides Alkali metal fluorides Optical materials Crystals Metal halides Rock salt crystal structure Fluorine compounds