Salt that has melted, often by heating to high temperatures
Molten FLiBe (2LiF ·BeF2 ) Molten salt is salt which is solid at standard temperature and pressure but liquified 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 801 °C (1,474 °F). A variety of eutectic mixtures have been developed with lower melting points:
Chlorides
Nitrates
Alkali metal nitrates are relatively low melting and thermally stable. The least stable, LiNO3 cesium nitrate melts at 414 °C (777 °F) and decomposes at 584 °C.[ 2]
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 :
MgO + C + Cl2 → MgCl2 + CO Electrolysis of the resulting molten magnesium chloride is conducted at 700 °C (1,292 °F):[ 6]
MgCl2 → Mg + Cl2 Aluminium metal is produced from aluminium oxides by electrolysis of a molten mixture of sodium hexafluoroaluminate and alumina at 950 °C (1,740 °F). This conversion is called the Hall-Haroult process .[ 7]
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.[ 8] [ 9]
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).[ 4]
Other uses
Molten chloride salt mixtures are commonly used as quenching baths for various alloy heat treatments , 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 ionic liquids ) 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,[ 10] 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
References
^ Johnson, Keith E.; Pagni, Richard M. (2012). "Liquid Salts for Reactions". Kirk-Othmer Encyclopedia of Chemical Technology . pp. 1–35. doi :10.1002/0471238961.liqupagn.a01 . ISBN 9780471484943 ^ Greenwood, Norman N. ; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann . p. 469. ISBN 978-0-08-037941-8 ^ "Molten salts properties "
^ a b 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.
^ Greenwood, Norman N. ; Earnshaw, Alan (1997). Chemistry of the Elements (2nd ed.). Butterworth-Heinemann . p. 90. ISBN 978-0-08-037941-8 ^ Kramer, Deborah A. (2010). "Magnesium and Magnesium Alloys". Kirk-Othmer Encyclopedia of Chemical Technology . pp. 1–55. doi :10.1002/0471238961.1301071423091219.a01.pub3 . ISBN 9780471484943 ^ Grams, G. W.; Conley, B.; Shaikh, T.; Atwood, D. A. (2004). "Aluminum Halides and Aluminum Nitrate". Kirk-Othmer Encyclopedia of Chemical Technology . doi :10.1002/0471238961.0112211307180113.a01.pub3 . ISBN 9780471484943 ^ "Molten Salts systems other applications link to Solar Power Plants" (PDF) . National Renewable Energy Laboratory (NREL). Archived from the original (PDF) on 2011-10-19. Retrieved 2011-09-06 .^ Bauer, Thomas; Odenthal, Christian; Bonk, Alexander (April 2021). "Molten Salt Storage for Power Generation" . Chemie Ingenieur Technik (in German). 93 (4): 534–546. doi :10.1002/cite.202000137 . ISSN 0009-286X . S2CID 233913583 . ^ Hurley, Frank H.; Wier, Thomas P. (1951). "Electrodeposition of Metals from Fused Quaternary Ammonium Salts" . Journal of the Electrochemical Society . 98 (5): 203. doi :10.1149/1.2778132 .
Bibliography
External links
