Aluminothermic reactions are exothermic chemical reactions using

aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It ha ...

as the

reducing agent In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are commonly reducing agents include the Earth me ...

at high temperature. The process is industrially useful for production of

alloy An alloy is a mixture of chemical elements of which at least one is a metal. Unlike chemical compounds with metallic bases, an alloy will retain all the properties of a metal in the resulting material, such as electrical conductivity, ductility, ...

s of

iron Iron () is a chemical element with symbol Fe (from la, ferrum) and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, right in f ...

. The most prominent example is the

thermite Thermite () is a pyrotechnic composition of metal powder and metal oxide. When ignited by heat or chemical reaction, thermite undergoes an exothermic reduction-oxidation (redox) reaction. Most varieties are not explosive, but can create brie ...

reaction between

iron oxides Iron oxides are chemical compounds composed of iron and oxygen. Several iron oxides are recognized. All are black magnetic solids. Often they are non-stoichiometric. Oxyhydroxides are a related class of compounds, perhaps the best known of whi ...

and aluminum to produce iron itself: : Fe₂O₃ + 2 Al → 2 Fe + Al₂O₃ This specific reaction is however not relevant to the most important application of aluminothermic reactions, the production of ferroalloys. For the production of iron, a cheaper reducing agent, coke, is used instead via the carbothermic reaction.

History

Aluminothermy started from the experiments of

Russia Russia (, , ), or the Russian Federation, is a List of transcontinental countries, transcontinental country spanning Eastern Europe and North Asia, Northern Asia. It is the List of countries and dependencies by area, largest country in the ...

n scientist

Nikolay Beketov Nikolay Nikolayevich Beketov (russian: Николай Николаевич Бекетов; , Alferovka (now Beketovka), Penza Governorate, Russian Empire – , St. Petersburg, Russian Empire) was a Russian Imperial physical chemist and metallur ...

at the

University of Kharkiv The Kharkiv University or Karazin University ( uk, Каразінський університет), or officially V. N. Karazin Kharkiv National University ( uk, Харківський національний університет імені ...

in Ukraine, who proved that

restored metals from their oxides under high temperatures. The reaction was first used for the carbon-free reduction of metal oxides. The reaction is highly exothermic, but it has a high

activation energy In chemistry and physics, activation energy is the minimum amount of energy that must be provided for compounds to result in a chemical reaction. The activation energy (''E''a) of a reaction is measured in joules per mole (J/mol), kilojoules p ...

since strong interatomic bonds in the solids must be broken first. The oxide was heated with aluminum in a crucible in a furnace. The runaway reaction made it possible to produce only small quantities of material.

Hans Goldschmidt Johannes Wilhelm "Hans" Goldschmidt (18 January 1861 – 21 May 1923) was a German chemist notable as the discoverer of the Thermite reaction. He was also co-owner of the Chemische Fabrik Th. Goldschmidt, as of 1911 Th. Goldschmidt AG (later to be ...

improved the aluminothermic process between 1893 and 1898, by igniting the mixture of fine metal oxide and aluminum 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.

Applications

The aluminothermic reaction is used for the production of several

ferroalloys Ferroalloy refers to various alloys of iron with a high proportion of one or more other elements such as manganese (Mn), aluminium (Al), or silicon (Si). They are used in the production of steels and alloys. The alloys impart distinctive qualiti ...

, for example

ferroniobium Ferroniobium is an important iron-niobium alloy, with a niobium content of 60-70%. It is the main source for niobium alloying of HSLA steel and covers more than 80% of the worldwide niobium production. The niobium is mined from pyrochlore deposits ...

from

niobium pentoxide Niobium pentoxide is the inorganic compound with the formula Nb2 O5. A colorless, insoluble, and fairly unreactive solid, it is the most widespread precursor for other compounds and materials containing niobium. It is predominantly used in alloyi ...

and

ferrovanadium Ferrovanadium (FeV) is an alloy formed by combining iron and vanadium with a vanadium content range of 35–85%. The production of this alloy results in a grayish silver crystalline solid that can be crushed into a powder called "ferrovanadium ...

from iron, vanadium(V) oxide, and aluminum. The process begins with the reduction of the oxide by the aluminum: :3 V₂O₅ + 10 Al → 5 Al₂O₃ + 6 V Other metals can be produced from their oxides in the same way. Aluminothermic reactions have been used for welding

rail tracks A railway track (British English and UIC terminology) or railroad track (American English), also known as permanent way or simply track, is the structure on a railway or railroad consisting of the rails, fasteners, railroad ties (sleeper ...

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. Velp-thermitewelding-1

References

{{Reflist Inorganic reactions Metallurgy Russian inventions Ukrainian inventions

History

Applications

See also

References