Aluminothermic reactions are exothermic chemical reactions using aluminium as the reducing agent at high temperature. The most prominent example is the thermite reaction between aluminium and iron oxides:
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The reaction was first used for the carbon free reduction of metaloxides. The reaction is highly exothermic, but it has a high activation energy since strong interatomic bonds in the solids must be broken first. The oxide was heated with aluminium in a crucible in a furnace. The runaway reaction made it only possible to produce small quantities of material. Hans Goldschmidt improved the aluminothermic process between 1893 and 1898, by igniting the mixture of fine metaloxid and aluminium powder by a starter reaction without heating the mixture externally. The process was patented in 1898 and used extensively in the later years for rail track welding.
A common use of this reaction is the welding of rail tracks on-site, useful for complex installations or local repairs that cannot be done using continuously welded rail.
Another common use is the welding of copper cables (wire) for use in direct burial (grounding/earthing) applications. It is still the only type of electrical connection recognized by the IEEE (IEEE, Std 80-2001) as continuous un-spliced cable.
The aluminothermic reaction is also used for the production of most of the ferroalloys, for example ferroniobium from niobium pentoxide.[1] Other metals can be produced in the same way.[2][3][4]
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