Molten salt

A salt melt is formed, when a salt is heated above its melting point. Molten salt include a variety of liquids. They are not widely known in everyday life, in manufacturing, they are used in many processes. Classic molten salt have a temperature of 150 ° C to 1300 ° C. More recently, low-melting salts ( ionic liquids ) can be used in molten salt below 80 ° C to replace the organic solvent. These ionic liquids but have generally different properties than conventional molten salts of ionic compounds.

Heat treatment and hardening technology

An application focus of molten salts is the thermal or thermochemical treatment of metals. Because of their temperature uniformity, they are often the medium of choice for annealing and hardening processes. The temperature of this melt can be selected within a wide range. The metal may be heated or cooled in a salt bath. Mainly melting salts such as Cyansalz be used.

Heat storage

In solar technology, the crystallization energy is used by thiosulfate to store heat. By means of water, which was heated in a solar collector on the roof is, melted salt. Later, the re- released during the recrystallization energy are used to heat the domestic water.

Heat transfer

Liquid salts are also used to transport at temperatures significantly above 100 ° C heat. In this case the pipe system need not be under pressure, such as with steam. Its scope is between the liquids water ( thermal ) oils and liquid metals. Be used, for example, mixtures of alkali metal nitrite and nitrate, whose melting point is at about 140 ° C.

Such as the salt bath employed in the vulcanization ( Salzbadvulkanisierung ). For her the rubber profile from the press is pressed directly into the molten salt. Thus, window seals, wiper blades and drive belts are made with smooth, dense surfaces. This process is carried out with molten alkali metal nitrates and nitrites or nitrates melted at temperatures between 240 ° C and 280 ° C.

Cleaning

Molten salts are also suitable for difficult to carry out cleaning ( thermochemical component cleaning). They are often used in mass production, mainly to clean metal parts from oil, grease, paint, coatings, oxides, waxes, glasses, plastics or foundry sand. So deposits are removed from operation with the help of salt melts at about gas turbine blades.

Flux in welding or soldering,

When brazing (ie no lead solder / solder) salts are used so that the liquid metal is better distributed.

Chemical reactions in molten salts

Some metals are recovered from the molten salt by melt electrolysis. In this case, the metal oxide or salt is dissolved in the melt and decomposed with the aid of electricity. The molten salt holding the liquid metal and prevent the immediate oxidation of the molten metal as it falls into the melt.

Examples include magnesium and aluminum production.

As the electrolyte

In molten carbonate fuel cells (MCFC ), a molten salt bath is from 580 ° C - 660 ° C, the electrolyte. Be used as alkali carbonates ( Li2CO3/K2CO3 ). Molten salts conduct electricity well, since the concentration of charge carriers is very high.

• Heat transfer
• Metallurgy