Sodium metal has relatively few commercial uses. The most important is as a heat exchange medium in fast breeder nuclear reactors. A heat exchange medium is a material that transports heat from one place to another. In the case of a nuclear reactor, the heat exchange medium absorbs heat produced in the reactor core and transfers that heat to a cooling unit. In the cooling unit, the heat is released to the atmosphere, is used to boil water to power an electrical generating unit, or is transferred to a system containing circulating water for release to the environment.
Liquid sodium is a highly effective heat exchange medium for a number of reasons. First, it has a high heat capacity (that is, it can absorb a lot of heat per gram of metal) and a low neutron absorption cross-section (that is, it does not take up neutrons from the reactor core). At the same time, the metal has a low melting point and a low viscosity, allowing it to flow through the system with relatively little resistance.
For many years, the most important commercial application of sodium metal was in the manufacture of antiknock additives such as tetraethyl and tetramethyl lead. An alloy of sodium and lead was used to react with alkyl chlorides (such as ethyl chloride) to produce these compounds. In 1959, about 70% of all the sodium produced in the United States was used for this purpose. As compounds of lead such as tetraethyl and tetramethyl lead have been phased out of use for environmental reasons, however, this use of sodium has declined dramatically.
Another important use of sodium metal is in the manufacture of other metals, such as zirconium and titanium. Originally, magnesium metal was the reducing agent of choice in these reactions, but sodium has recently become increasingly popular in the preparation of both metals. When sodium is heated with a chloride of one of these metals, it replaces (reduces) the metal to yield the pure metal and sodium chloride.
About 10% of all sodium produced is used to make specialized compounds such as sodium hydride (NaH), sodium peroxide (Na2O2), and sodium alkoxides (NaOR). Small amounts of the metal are used as a catalyst in the manufacture of synthetic elastomers.