Molten salt is salt which is solid at standard temperature and pressure but liquid due to elevated temperature. A salt that is liquid even at standard temperature and pressure is usually called a room-temperature ionic liquid, and molten salts are technically a class of ionic liquids.
Examples
As a reference, molten
sodium chloride,
table salt has a melting point (m.p.) of . A variety of
eutectic mixture have been developed with lower melting points:
Chlorides
Nitrates
Alkali metal nitrates are relatively low melting and thermally stable. The least stable,
lithium nitrate (m.p. ) decomposes only at . At the other extreme,
cesium nitrate melts at and decomposes at 584 °C.
Uses
Molten salts have a variety of uses.
Production of magnesium and aluminium
One industrial application is the production of magnesium, which begins with production of magnesium chloride by chlorination of
magnesium oxide:
Electrolysis of the resulting molten magnesium chloride is conducted at :
Aluminium metal is produced from aluminium oxides by electrolysis of a molten mixture of sodium hexafluoroaluminate and alumina at . This conversion is called the Hall-Héroult process.
Heat transfer
Molten salts (fluoride, chloride, and
nitrate) can be used as heat transfer fluids as well as for
thermal storage. This thermal storage is used in concentrated solar power plants.
Molten-salt reactors are a type of nuclear reactor that uses molten salt(s) as a coolant or as a solvent in which the fissile material is dissolved. 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.]
Other uses
Molten
chloride salt mixtures are commonly used as
quenching baths for various alloy
, such as annealing and
martempering of
steel.
Cyanide and chloride salt mixtures are used for surface modification of alloys such as
carburizing and
nitrocarburizing of steel.
Cryolite (a fluoride salt) is used as a solvent 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 of nuclear fuel.
Ambient-temperature molten salts
Ambient-temperature molten salts (also known as
) are present in the liquid phase at standard conditions for temperature and pressure. Examples of such salts include
N-ethylpyridinium
bromide and aluminium chloride mix, discovered in 1951,
and ethylammonium nitrate discovered by
Paul Walden. Other ionic liquids take advantage of asymmetrical quaternary ammonium cations like alkylated
imidazolium ions, and large, branched anions like the
bistriflimide ion.
See also
-
Electromagnetic pump
-
Ionic liquid
-
Molten-salt battery
-
Molten salt oxidation
-
Molten-salt reactor
-
Parabolic trough
-
United States Department of Energy International Energy Storage Database
Bibliography
External links
