Molten salt is

salt Salt is a mineral composed primarily of sodium chloride (NaCl), a chemical compound belonging to the larger class of salts; salt in the form of a natural crystalline mineral is known as rock salt or halite. Salt is present in vast quant ...

which is solid at

standard temperature and pressure Standard temperature and pressure (STP) are standard sets of conditions for experimental measurements to be established to allow comparisons to be made between different sets of data. The most used standards are those of the International Union ...

but enters the

liquid phase A liquid is a nearly incompressible fluid that conforms to the shape of its container but retains a (nearly) constant volume independent of pressure. As such, it is one of the four fundamental states of matter (the others being solid, gas, ...

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.NaCl CID 5234, 4.2.14 Other Experimental Properties
NaCl Other Chemical/Physical Properties
A salt that is normally liquid even at standard temperature and pressure is usually called a room temperature

ionic liquid An ionic liquid (IL) is a salt in the liquid state. In some contexts, the term has been restricted to salts whose melting point is below a specific temperature, such as . While ordinary liquids such as water and gasoline are predominantly made of ...

, and so technically molten salts are a class of ionic liquids.

Uses

Molten salts have a variety of uses. Molten

chloride The chloride ion is the anion (negatively charged ion) Cl−. It is formed when the element chlorine (a halogen) gains an electron or when a compound such as hydrogen chloride is dissolved in water or other polar solvents. Chloride s ...

salt mixtures are commonly used as baths in devices called molten salt reactors for various alloy heat treatments, such as annealing and martempering of

steel Steel is an alloy made up of iron with added carbon to improve its strength and fracture resistance compared to other forms of iron. Many other elements may be present or added. Stainless steels that are corrosion- and oxidation-resistan ...

Cyanide Cyanide is a naturally occurring, rapidly acting, toxic chemical that can exist in many different forms. In chemistry, a cyanide () is a chemical compound that contains a functional group. This group, known as the cyano group, consists of ...

and chloride salt mixtures are used for surface modification of alloys such as

carburizing Carburising, carburizing (chiefly American English), or carburisation is a heat treatment process in which iron or steel absorbs carbon while the metal is heated in the presence of a carbon-bearing material, such as charcoal or carbon monoxide. ...

and

nitrocarburizing Ferritic nitrocarburizing or FNC, also known by the proprietary names Tenifer, Tufftride and Melonite as well as ARCOR,Other trade names include Tuffride/ Tuffrider, QPQ, Sulfinuz, Sursulf, Meli 1, and Nitride, among others is a range of proprie ...

of steel. Cryolite (a

fluoride Fluoride (). According to this source, is a possible pronunciation in British English. is an inorganic, monatomic anion of fluorine, with the chemical formula (also written ), whose salts are typically white or colorless. Fluoride salts ty ...

salt) is used as a

solvent A solvent (s) (from the Latin '' solvō'', "loosen, untie, solve") is a substance that dissolves a solute, resulting in a solution. A solvent is usually a liquid but can also be a solid, a gas, or a supercritical fluid. Water is a solvent for ...

for aluminium oxide in the production of aluminium in the Hall-Héroult process. Fluoride, chloride, and hydroxide salts can be used as solvents in

pyroprocessing Pyroprocessing (from Greek Πυρος = ''fire'') is a process in which materials are subjected to high temperatures (typically over 800 °C) in order to bring about a chemical or physical change. Pyroprocessing includes such terms as ore-ro ...

nuclear fuel Nuclear fuel is material used in nuclear power stations to produce heat to power turbines. Heat is created when nuclear fuel undergoes nuclear fission. Most nuclear fuels contain heavy fissile actinide elements that are capable of undergo ...

. Molten salts (fluoride, chloride, and

nitrate Nitrate is a polyatomic ion with the chemical formula . Salts containing this ion are called nitrates. Nitrates are common components of fertilizers and explosives. Almost all inorganic nitrates are soluble in water. An example of an insolu ...

) can be used as heat transfer fluids as well as for

thermal storage Thermal energy storage (TES) is achieved with widely different technologies. Depending on the specific technology, it allows excess thermal energy to be stored and used hours, days, months later, at scales ranging from the individual process, ...

. This thermal storage is commonly used in

concentrated solar power Concentrated solar power (CSP, also known as concentrating solar power, concentrated solar thermal) systems generate solar power by using mirrors or lenses to concentrate a large area of sunlight into a receiver. Electricity is generated when ...

plants. A commonly used thermal salt is the eutectic mixture of 60%

sodium nitrate Sodium nitrate is the chemical compound with the formula . This alkali metal nitrate salt is also known as Chile saltpeter (large deposits of which were historically mined in Chile) to distinguish it from ordinary saltpeter, potassium nitrate. ...

and 40%

potassium nitrate Potassium nitrate is a chemical compound with the chemical formula . This alkali metal nitrate salt is also known as Indian saltpetre (large deposits of which were historically mined in India). It is an ionic salt of potassium ions K+ and ...

, which can be used as liquid between 260-550 °C. It has a

heat of fusion In thermodynamics, the enthalpy of fusion of a substance, also known as (latent) heat of fusion, is the change in its enthalpy resulting from providing energy, typically heat, to a specific quantity of the substance to change its state from a s ...

of 161 J/g, and a

heat capacity Heat capacity or thermal capacity is a physical property of matter, defined as the amount of heat to be supplied to an object to produce a unit change in its temperature. The SI unit of heat capacity is joule per kelvin (J/K). Heat cap ...

of 1.53 J/(g K). Experimental salts using lithium can be formed that have a melting point of 116 °C while still having a heat capacity of 1.54 J/(g K).Reddy, Ramana G.
Novel Molten Salts Thermal Energy Storage for Concentrating Solar Power Generation
page 9 ''University of Alabama College of Engineering''. Retrieved 9 December 2014. Salts may cost $1,000 per ton, and a typical plant may use 30,000 tons of salt.Bullis, Kevin.
Cheap Solar Power at Night
''

MIT Technology Review ''MIT Technology Review'' is a bimonthly magazine wholly owned by the Massachusetts Institute of Technology, and editorially independent of the university. It was founded in 1899 as ''The Technology Review'', and was re-launched without "The" in ...

'', 12 March 2012. Retrieved 9 December 2014.

Ambient temperature molten salts

Ambient temperature molten salts (also known as

ionic liquids An ionic liquid (IL) is a salt in the liquid state. In some contexts, the term has been restricted to salts whose melting point is below a specific temperature, such as . While ordinary liquids such as water and gasoline are predominantly made of ...

) are present in the liquid phase at

standard conditions for temperature and pressure Standard temperature and pressure (STP) are standard sets of conditions for experimental measurements to be established to allow comparisons to be made between different sets of data. The most used standards are those of the International Union ...

. Examples of such salts include ''N''-ethylpyridinium

bromide A bromide ion is the negatively charged form (Br−) of the element bromine, a member of the halogens group on the periodic table. Most bromides are colorless. Bromides have many practical roles, being found in anticonvulsants, flame-retardant ...

and

aluminium chloride Aluminium chloride, also known as aluminium trichloride, is an inorganic compound with the formula . It forms hexahydrate with the formula , containing six water molecules of hydration. Both are colourless crystals, but samples are often contam ...

mix, discovered in 1951Hurley, F. H.; Wier, T. P. ''J. Electrochem. Soc.'' 1951, 98, 203. and ethylammonium nitrate discovered by

Paul Walden Paul Walden ( lv, Pauls Valdens; russian: Павел Иванович Вальден; german: Paul von Walden; 26 July 1863 – 22 January 1957) was a Russian, Latvian and German chemist known for his work in stereochemistry and history of chem ...

. Other ionic liquids take advantage of asymmetrical quaternary ammonium cations like alkylated imidazolium ions, and large, branched anions like the

bistriflimide Bistriflimide, also known variously as bis(trifluoromethane)sulfonimide, bis(trifluoromethanesulfonyl)amide, bis(trifluoromethanesulfonyl)imidate (and variations thereof), informally and somewhat inaccurately as triflimide or triflimidate'','' or ...

ion.

References

External links

Journal_of_Chemical_Thermodynamics
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br>Proc. Roy. Soc.

Bibliography

C.F. Baes, ''The chemistry and thermodynamics of molten salt reactor fuels'', Proc. AIME Nuclear Fuel Reprocessing Symposium, Ames, Iowa, USA, 1969 (August 25) {{Authority control Energy storage Metallurgical processes Inorganic solvents Ionic liquids

Uses

Ambient temperature molten salts

See also

References

External links

Bibliography