Thermite
Overview
 
Thermite is a pyrotechnic composition
Pyrotechnic composition
A pyrotechnic composition is a substance or mixture of substances designed to produce an effect by heat, light, sound, gas or smoke or a combination of these, as a result of non-detonative self-sustaining exothermic chemical reactions...

 of a metal powder
Powder metallurgy
Powder metallurgy is the process of blending fine powdered materials, pressing them into a desired shape , and then heating the compressed material in a controlled atmosphere to bond the material . The powder metallurgy process generally consists of four basic steps: powder manufacture, powder...

 and a metal oxide that produces an exothermic oxidation-reduction reaction known as a thermite reaction. If aluminium is the reducing agent it is called an aluminothermic reaction
Aluminothermic reaction
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:-History:...

. Most varieties are not explosive, but can create short bursts of extremely high temperatures focused on a very small area for a short period of time. The thermite is simply a mixture of metal, often called the "fuel" and an oxidizer.
Encyclopedia
Thermite is a pyrotechnic composition
Pyrotechnic composition
A pyrotechnic composition is a substance or mixture of substances designed to produce an effect by heat, light, sound, gas or smoke or a combination of these, as a result of non-detonative self-sustaining exothermic chemical reactions...

 of a metal powder
Powder metallurgy
Powder metallurgy is the process of blending fine powdered materials, pressing them into a desired shape , and then heating the compressed material in a controlled atmosphere to bond the material . The powder metallurgy process generally consists of four basic steps: powder manufacture, powder...

 and a metal oxide that produces an exothermic oxidation-reduction reaction known as a thermite reaction. If aluminium is the reducing agent it is called an aluminothermic reaction
Aluminothermic reaction
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:-History:...

. Most varieties are not explosive, but can create short bursts of extremely high temperatures focused on a very small area for a short period of time. The thermite is simply a mixture of metal, often called the "fuel" and an oxidizer. Its form of action is very similar to other fuel-oxidizer mixtures like black powder
Gunpowder
Gunpowder, also known since in the late 19th century as black powder, was the first chemical explosive and the only one known until the mid 1800s. It is a mixture of sulfur, charcoal, and potassium nitrate - with the sulfur and charcoal acting as fuels, while the saltpeter works as an oxidizer...

.

Thermites can be a diverse class of compositions. Some "fuels" that can be used include aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

, magnesium
Magnesium
Magnesium is a chemical element with the symbol Mg, atomic number 12, and common oxidation number +2. It is an alkaline earth metal and the eighth most abundant element in the Earth's crust and ninth in the known universe as a whole...

, calcium
Calcium
Calcium is the chemical element with the symbol Ca and atomic number 20. It has an atomic mass of 40.078 amu. Calcium is a soft gray alkaline earth metal, and is the fifth-most-abundant element by mass in the Earth's crust...

, titanium
Titanium
Titanium is a chemical element with the symbol Ti and atomic number 22. It has a low density and is a strong, lustrous, corrosion-resistant transition metal with a silver color....

, zinc
Zinc
Zinc , or spelter , is a metallic chemical element; it has the symbol Zn and atomic number 30. It is the first element in group 12 of the periodic table. Zinc is, in some respects, chemically similar to magnesium, because its ion is of similar size and its only common oxidation state is +2...

, silicon
Silicon
Silicon is a chemical element with the symbol Si and atomic number 14. A tetravalent metalloid, it is less reactive than its chemical analog carbon, the nonmetal directly above it in the periodic table, but more reactive than germanium, the metalloid directly below it in the table...

, and boron
Boron
Boron is the chemical element with atomic number 5 and the chemical symbol B. Boron is a metalloid. Because boron is not produced by stellar nucleosynthesis, it is a low-abundance element in both the solar system and the Earth's crust. However, boron is concentrated on Earth by the...

 and others. One commonly-used fuel in thermite mixtures is aluminium
Aluminium
Aluminium or aluminum is a silvery white member of the boron group of chemical elements. It has the symbol Al, and its atomic number is 13. It is not soluble in water under normal circumstances....

, because of its high boiling point
Boiling point
The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....

. The oxidizers can be boron(III) oxide, silicon(IV) oxide, chromium(III) oxide
Chromium(III) oxide
Chromium oxide is the inorganic compound of the formula Cr2O3. It is one of principal oxides of chromium and is used as a pigment. In nature, it occurs as the rare mineral eskolaite.-Structure and properties:...

, manganese(IV) oxide
Manganese(IV) oxide
Manganese oxide is the inorganic compound with the formula . This blackish or brown solid occurs naturally as the mineral pyrolusite, which is the main ore of manganese and a component of manganese nodules. The principal use for MnO2 is for dry-cell batteries, such as the alkaline battery and the...

, iron(III) oxide
Iron(III) oxide
Iron oxide or ferric oxide is the inorganic compound with the formula Fe2O3. It is one of the three main oxides of iron, the other two being iron oxide , which is rare, and iron oxide , which also occurs naturally as the mineral magnetite. As the mineral known as hematite, Fe2O3 is the main...

, iron(II,III) oxide
Iron(II,III) oxide
Iron oxide is the chemical compound with formula Fe3O4. It is one of a number of iron oxides, the others being iron oxide , which is rare, and iron oxide also known as hematite. It occurs in nature as the mineral magnetite. It contains both Fe2+ and Fe3+ ions and is sometimes formulated as FeO ∙...

, copper(II) oxide
Copper(II) oxide
Copper oxide or cupric oxide is the higher oxide of copper. As a mineral, it is known as tenorite.-Chemistry:It is a black solid with an ionic structure which melts above 1200 °C with some loss of oxygen...

, and lead(II,III,IV) oxide and others.

Chemical reactions

The aluminium reduces the oxide of another metal
Metal
A metal , is an element, compound, or alloy that is a good conductor of both electricity and heat. Metals are usually malleable and shiny, that is they reflect most of incident light...

, most commonly iron oxide
Iron oxide
Iron oxides are chemical compounds composed of iron and oxygen. All together, there are sixteen known iron oxides and oxyhydroxides.Iron oxides and oxide-hydroxides are widespread in nature, play an important role in many geological and biological processes, and are widely utilized by humans, e.g.,...

, because aluminium is highly reactive:
Fe2O3 + 2Al → 2Fe + Al2O3


The products are aluminium oxide
Aluminium oxide
Aluminium oxide is an amphoteric oxide with the chemical formula 23. It is commonly referred to as alumina, or corundum in its crystalline form, as well as many other names, reflecting its widespread occurrence in nature and industry...

, free elemental iron
Iron
Iron is a chemical element with the symbol Fe and atomic number 26. It is a metal in the first transition series. It is the most common element forming the planet Earth as a whole, forming much of Earth's outer and inner core. It is the fourth most common element in the Earth's crust...

, and a large amount of heat
Heat
In physics and thermodynamics, heat is energy transferred from one body, region, or thermodynamic system to another due to thermal contact or thermal radiation when the systems are at different temperatures. It is often described as one of the fundamental processes of energy transfer between...

. The reactants are commonly powdered
Powder (substance)
A powder is a dry,thick bulk solid composed of a large number of very fine particles that may flow freely when shaken or tilted. Powders are a special sub-class of granular materials, although the terms powder and granular are sometimes used to distinguish separate classes of material...

 and mixed with a binder to keep the material solid and prevent separation.

The reaction is used for thermite welding, often used to join rail tracks. Other metal oxides can be used, such as chromium oxide, to generate the given metal in its elemental form. Copper
Copper
Copper is a chemical element with the symbol Cu and atomic number 29. It is a ductile metal with very high thermal and electrical conductivity. Pure copper is soft and malleable; an exposed surface has a reddish-orange tarnish...

 thermite, using copper oxide, is used for creating electric joints in a process called cadwelding
Cadwelding
Exothermic welding, also known as exothermic bonding, thermite welding , and thermit welding, is a welding process for joining two electrical conductors, that employs superheated copper alloy to permanently join the conductors...

:
3CuO + 2Al → 3Cu + Al2O3


Some thermite-like mixtures are used as pyrotechnic initiator
Pyrotechnic initiator
A pyrotechnic initiator is a device containing a pyrotechnic composition used primarily to ignite other, more difficult-to-ignite materials, e.g. thermites, gas generators, and solid-fuel rockets...

s such as fireworks
Fireworks
Fireworks are a class of explosive pyrotechnic devices used for aesthetic and entertainment purposes. The most common use of a firework is as part of a fireworks display. A fireworks event is a display of the effects produced by firework devices...

.

Thermites with nanosized particles are described through a variety of terms, such as metastable intermolecular composites, super-thermite, nano-thermite, and nanocomposite energetic materials.

History

The thermite (thermit) reaction was discovered in 1893 and patent
Patent
A patent is a form of intellectual property. It consists of a set of exclusive rights granted by a sovereign state to an inventor or their assignee for a limited period of time in exchange for the public disclosure of an invention....

ed in 1895 by German
Germany
Germany , officially the Federal Republic of Germany , is a federal parliamentary republic in Europe. The country consists of 16 states while the capital and largest city is Berlin. Germany covers an area of 357,021 km2 and has a largely temperate seasonal climate...

 chemist
Chemist
A chemist is a scientist trained in the study of chemistry. Chemists study the composition of matter and its properties such as density and acidity. Chemists carefully describe the properties they study in terms of quantities, with detail on the level of molecules and their component atoms...

 Hans Goldschmidt
Hans Goldschmidt
Johannes Wilhelm "Hans" Goldschmidt was a German chemist.Born in Berlin, he was a student of Robert Bunsen. His father, Theodor Goldschmidt, was the founder of the chemical company Chemische Fabrik Th...

. Consequently, the reaction is sometimes called the "Goldschmidt reaction" or "Goldschmidt process". Dr. Goldschmidt was originally interested in producing very pure metals by avoiding the use of carbon
Carbon
Carbon is the chemical element with symbol C and atomic number 6. As a member of group 14 on the periodic table, it is nonmetallic and tetravalent—making four electrons available to form covalent chemical bonds...

 in smelting
Smelting
Smelting is a form of extractive metallurgy; its main use is to produce a metal from its ore. This includes iron extraction from iron ore, and copper extraction and other base metals from their ores...

, but he soon discovered the value of thermite in welding
Welding
Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes...

.

The first commercial application of thermite was the welding of tram
Tram
A tram is a passenger rail vehicle which runs on tracks along public urban streets and also sometimes on separate rights of way. It may also run between cities and/or towns , and/or partially grade separated even in the cities...

 tracks in Essen, Germany, in 1899.

Types

Red iron(III) oxide (Fe2O3, commonly known as rust
Rust
Rust is a general term for a series of iron oxides. In colloquial usage, the term is applied to red oxides, formed by the reaction of iron and oxygen in the presence of water or air moisture...

) is the most common iron oxide used in thermite. Magnetite
Magnetite
Magnetite is a ferrimagnetic mineral with chemical formula Fe3O4, one of several iron oxides and a member of the spinel group. The chemical IUPAC name is iron oxide and the common chemical name is ferrous-ferric oxide. The formula for magnetite may also be written as FeO·Fe2O3, which is one part...

 also works. Other oxides are occasionally used, such as MnO2
Manganese(IV) oxide
Manganese oxide is the inorganic compound with the formula . This blackish or brown solid occurs naturally as the mineral pyrolusite, which is the main ore of manganese and a component of manganese nodules. The principal use for MnO2 is for dry-cell batteries, such as the alkaline battery and the...

 in manganese thermite, Cr2O3
Chromium(III) oxide
Chromium oxide is the inorganic compound of the formula Cr2O3. It is one of principal oxides of chromium and is used as a pigment. In nature, it occurs as the rare mineral eskolaite.-Structure and properties:...

 in chromium thermite, or copper(II) oxide in copper thermite, but only for specialized purposes. All of these examples use aluminium as the reactive metal. Fluoropolymers can be used in special formulations, Teflon
Polytetrafluoroethylene
Polytetrafluoroethylene is a synthetic fluoropolymer of tetrafluoroethylene that finds numerous applications. PTFE is most well known by the DuPont brand name Teflon....

 with magnesium or aluminium being a relatively common example. Magnesium/teflon/viton
Magnesium/Teflon/Viton
Magnesium/Teflon/Viton is a pyrolant. Teflon and Viton are trademarks of DuPont for polytetrafluoroethylene, n, and vinylidenfluoride-hexafluoroisopropene-copolymer, nn.-History:...

 is another pyrolant
Pyrolant
Pyrolant, from the Greek word pyros to describe energetic materials that generate hot flames upon combustion. Pyrolants are metal-based pyrotechnic compositions containing virtually any oxidizer....

 of this type.

In principle, any reactive metal could be used instead of aluminium. This is rarely done, however, because the properties of aluminium are nearly ideal for this reaction. It is by far the cheapest of the highly reactive metals; it also forms a passivation
Passivation
Passivation is the process of making a material "passive", and thus less reactive with surrounding air, water, or other gases or liquids. The goal is to inhibit corrosion, whether for structural or cosmetic reasons. Passivation of metals is usually achieved by the deposition of a layer of oxide...

 layer making it safer to handle than many other reactive metals. The melting
Melting point
The melting point of a solid is the temperature at which it changes state from solid to liquid. At the melting point the solid and liquid phase exist in equilibrium. The melting point of a substance depends on pressure and is usually specified at standard atmospheric pressure...

 and boiling
Boiling point
The boiling point of an element or a substance is the temperature at which the vapor pressure of the liquid equals the environmental pressure surrounding the liquid....

 points of aluminium also make it ideal for thermite reactions. Its relatively low melting point (660 °C (1,220 °F)) means that it is easy to melt the metal, so that the reaction can occur mainly in the liquid phase and thus proceeds fairly quickly. At the same time, its high boiling point (2519 °C (4,566.2 °F)) enables the reaction to reach very high temperatures, since several processes tend to limit the maximum temperature to just below the boiling point. Such a high boiling point is common among transition metals (e.g., iron and copper boil at 2887 °C (5,228.6 °F) and 2582 °C (4,679.6 °F) respectively), but is especially unusual among the highly reactive metals (cf. magnesium and sodium
Sodium
Sodium is a chemical element with the symbol Na and atomic number 11. It is a soft, silvery-white, highly reactive metal and is a member of the alkali metals; its only stable isotope is 23Na. It is an abundant element that exists in numerous minerals, most commonly as sodium chloride...

 which boil at 1090 °C (1,994 °F) and 883 °C (1,621.4 °F) respectively). Further, the low density of the aluminium oxide formed as a result of the reaction tends to cause it to float on the iron, reducing contamination of the weld.

Although the reactants are stable at room temperature, they burn with an extremely intense exothermic reaction
Exothermic reaction
An exothermic reaction is a chemical reaction that releases energy in the form of light or heat. It is the opposite of an endothermic reaction. Expressed in a chemical equation:-Overview:...

 when they are heated to ignition temperature. The products emerge as liquids due to the high temperatures reached (up to 2500 °C (4,532 °F) with iron(III) oxide)—although the actual temperature reached depends on how quickly heat can escape to the surrounding environment. Thermite contains its own supply of oxygen and does not require any external source of air. Consequently, it cannot be smothered and may ignite in any environment, given sufficient initial heat. It will burn well while wet and cannot be easily extinguished with water, although enough water will remove heat and may stop the reaction. Small amounts of water will boil before reaching the reaction. Although thermite is used for welding underwater, this can produce hydrogen which will in turn burn also.

Ignition

Metals are capable of burning under the right conditions, similar to the combustion
Combustion
Combustion or burning is the sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat and conversion of chemical species. The release of heat can result in the production of light in the form of either glowing or a flame...

 process of wood or gasoline. In fact, rust is the result of oxidation of steel
Steel
Steel is an alloy that consists mostly of iron and has a carbon content between 0.2% and 2.1% by weight, depending on the grade. Carbon is the most common alloying material for iron, but various other alloying elements are used, such as manganese, chromium, vanadium, and tungsten...

 or iron at very slow rates. A thermite reaction is a process in which the correct mixture of metallic fuels are combined and ignited. Ignition itself requires extremely high temperatures.

Ignition of a thermite reaction normally requires only a simple child's sparkler
Sparkler
A sparkler is a type of hand-held firework that burns slowly while emitting colored flames, sparks, and other effects.In the United Kingdom, a sparkler is often used by children at bonfire and fireworks displays on Guy Fawkes Night, the fifth of November, and in the United States on Independence...

 or easily obtainable magnesium ribbon, but may require persistent efforts, as ignition can be unreliable and unpredictable. These temperatures cannot be reached with conventional black powder fuses, nitrocellulose
Nitrocellulose
Nitrocellulose is a highly flammable compound formed by nitrating cellulose through exposure to nitric acid or another powerful nitrating agent. When used as a propellant or low-order explosive, it is also known as guncotton...

 rods, detonator
Detonator
A detonator is a device used to trigger an explosive device. Detonators can be chemically, mechanically, or electrically initiated, the latter two being the most common....

s, pyrotechnic initiators, or other common igniting substances. Even when the thermite is hot enough to glow bright red, it will not ignite as it must be at or near white-hot to initiate the reaction. It is possible to start the reaction using a propane torch
Propane torch
A propane torch is a tool for burning the flammable gas propane . The maximum adiabatic flame temperature a propane torch can achieve with air is 2,268 kelvins...

 if done correctly.

Often, strips of magnesium metal are used as fuses. Because metals burn without releasing cooling gases, they can potentially burn at extremely high temperatures. Reactive metals such as magnesium can easily reach temperatures sufficiently high for thermite ignition. Magnesium ignition remains popular among amateur thermite users, mainly because it can be easily obtained.

The reaction between potassium permanganate
Potassium permanganate
Potassium permanganate is an inorganic chemical compound with the formula KMnO4. It is a salt consisting of K+ and MnO4− ions. Formerly known as permanganate of potash or Condy's crystals, it is a strong oxidizing agent. It dissolves in water to give intensely purple solutions, the...

 and glycerol
Glycerol
Glycerol is a simple polyol compound. It is a colorless, odorless, viscous liquid that is widely used in pharmaceutical formulations. Glycerol has three hydroxyl groups that are responsible for its solubility in water and its hygroscopic nature. The glycerol backbone is central to all lipids...

 or ethylene glycol
Ethylene glycol
Ethylene glycol is an organic compound widely used as an automotive antifreeze and a precursor to polymers. In its pure form, it is an odorless, colorless, syrupy, sweet-tasting liquid...

 is used as an alternative to the magnesium method. When these two substances mix, a spontaneous reaction will begin, slowly increasing the temperature of the mixture until flames are produced. The heat released by the oxidation of glycerine is sufficient to initiate a thermite reaction.

Apart from magnesium ignition, some amateurs also choose to use sparklers to ignite the thermite mixture. These reach the necessary temperatures and provide enough time before the burning point reaches the sample. However, this can be a dangerous method, as the iron sparks, like the magnesium strips, burn at thousands of degrees and can ignite the thermite even though the sparkler itself is not in contact with it. This is especially dangerous with finely powdered thermite.

Similarly, finely-powdered thermite can be ignited by a regular flint spark lighter
Flint spark lighter
A flint spark lighter is a type of lighter used in many applications to safely light a gaseous fuel to start a flame...

, as the sparks are burning metal (in this case, the highly-reactive rare-earth metals lanthanum
Lanthanum
Lanthanum is a chemical element with the symbol La and atomic number 57.Lanthanum is a silvery white metallic element that belongs to group 3 of the periodic table and is the first element of the lanthanide series. It is found in some rare-earth minerals, usually in combination with cerium and...

 and cerium
Cerium
Cerium is a chemical element with the symbol Ce and atomic number 58. It is a soft, silvery, ductile metal which easily oxidizes in air. Cerium was named after the dwarf planet . Cerium is the most abundant of the rare earth elements, making up about 0.0046% of the Earth's crust by weight...

). Therefore it is unsafe to strike a lighter close to thermite.

A stoichiometric mixture of finely powdered iron(III) oxide and aluminium may be ignited using ordinary red-tipped book match
Match
A match is a tool for starting a fire under controlled conditions. A typical modern match is made of a small wooden stick or stiff paper. One end is coated with a material that can be ignited by frictional heat generated by striking the match against a suitable surface...

es by partially embedding one match head in the mixture, and igniting that match head with another match, preferably held with tongs in gloves to prevent flash burn
Flash burn
Flash burn can mean:*Arc eye, also called corneal flash burn*The effect that in a nuclear explosion of sufficient magnitude, the majority of damage is done by light and thermal radiation...

s.

Civilian uses

Thermite reactions have many uses. Thermite is not an explosive; instead it operates by exposing a very small area of metal to extremely high temperatures. Intense heat focused on a small spot can be used to cut through metal or weld metal components together both by melting metal from the components, and by injecting molten metal from the thermite reaction itself.

Thermite may be used for repair by the welding in-place of thick steel sections such as locomotive
Locomotive
A locomotive is a railway vehicle that provides the motive power for a train. The word originates from the Latin loco – "from a place", ablative of locus, "place" + Medieval Latin motivus, "causing motion", and is a shortened form of the term locomotive engine, first used in the early 19th...

 axle
Axle
An axle is a central shaft for a rotating wheel or gear. On wheeled vehicles, the axle may be fixed to the wheels, rotating with them, or fixed to its surroundings, with the wheels rotating around the axle. In the former case, bearings or bushings are provided at the mounting points where the axle...

-frames where the repair can take place without removing the part from its installed location.

Thermite can be used for quickly cutting or welding steel such as rail tracks
Rail tracks
The track on a railway or railroad, also known as the permanent way, is the structure consisting of the rails, fasteners, sleepers and ballast , plus the underlying subgrade...

, without requiring complex or heavy equipment. However, defects such as slag inclusions and voids (holes) are often present in such welded junctions and great care is needed to operate the process successfully. Care must also be taken to ensure that the rails remain straight, without resulting in dipped joints, which can cause wear on high speed and heavy axle load lines.

A thermite reaction, when used to purify the ore
Ore
An ore is a type of rock that contains minerals with important elements including metals. The ores are extracted through mining; these are then refined to extract the valuable element....

s of some metals, is called the thermite process, or aluminothermic reaction. An adaptation of the reaction, used to obtain pure uranium
Uranium
Uranium is a silvery-white metallic chemical element in the actinide series of the periodic table, with atomic number 92. It is assigned the chemical symbol U. A uranium atom has 92 protons and 92 electrons, of which 6 are valence electrons...

, was developed as part of the Manhattan Project
Manhattan Project
The Manhattan Project was a research and development program, led by the United States with participation from the United Kingdom and Canada, that produced the first atomic bomb during World War II. From 1942 to 1946, the project was under the direction of Major General Leslie Groves of the US Army...

 at Ames Laboratory
Ames Laboratory
Ames Laboratory is a United States Department of Energy national laboratory located in Ames, Iowa. The Laboratory conducts research into various areas of national concern, including the synthesis and study of new materials, energy resources, high-speed computer design, and environmental cleanup...

 under the direction of Frank Spedding
Frank Spedding
Frank Harold Spedding was a Canadian chemist who led a group of chemists at Ames Laboratory which developed an efficient process for obtaining high purity uranium from uranium halides. The general technique is known as the Thermite process, or more specifically, the Ames process...

. It is sometimes called the Ames process
Ames process
The Ames process is a process by which pure uranium metal is obtained. It can be achieved by mixing any of the uranium halides with magnesium metal powder or aluminium metal powder.- History :...

.

Copper thermite is used for welding together thick copper wires for the purpose of electrical connections. It is used extensively by the electrical utilities and telecommunications industries (exothermic welded connections).

Military uses

Thermite hand grenade
Hand grenade
A hand grenade is any small bomb that can be thrown by hand. Hand grenades are classified into three categories, explosive grenades, chemical and gas grenades. Explosive grenades are the most commonly used in modern warfare, and are designed to detonate after impact or after a set amount of time...

s and charges are typically used by armed forces in both an anti-materiel
Materiel
Materiel is a term used in English to refer to the equipment and supplies in military and commercial supply chain management....

 role and in the partial destruction of equipment; the latter being common when time is not available for safer or more thorough methods. For example, thermite can be used for the emergency destruction of cryptographic equipment when there is a danger that it might be captured by enemy troops. Because standard iron-thermite is difficult to ignite, burns with practically no flame and has a small radius of action, standard thermite is rarely used on its own as an incendiary composition. It is more usually employed with other ingredients added to enhance its incendiary effects. Thermate-TH3
Thermate
Thermate is a variation of thermite and is an incendiary pyrotechnic composition that can generate short bursts of very high temperatures focused on a small area for a short period of time. It is used primarily in incendiary grenades....

 is a mixture of thermite and pyrotechnic additives which have been found to be superior to standard thermite for incendiary purposes. Its composition by weight is generally about 68.7% thermite, 29.0% barium nitrate
Barium nitrate
Barium nitrate with chemical formula Ba2 is a salt of barium and the nitrate ion.Barium nitrate exists as a white solid at room temperature. It is soluble in water, and like other soluble barium compounds, is toxic and should be handled with care...

, 2.0% sulfur
Sulfur
Sulfur or sulphur is the chemical element with atomic number 16. In the periodic table it is represented by the symbol S. It is an abundant, multivalent non-metal. Under normal conditions, sulfur atoms form cyclic octatomic molecules with chemical formula S8. Elemental sulfur is a bright yellow...

, and 0.3% of a binder
Binder (material)
-See also:*Adhesive or Glue*Cement*Paint...

 (such as PBAN
PBAN
Polybutadiene acrylonitrile copolymer, also noted as polybutadiene — acrylic acid — acrylonitrile terpolymer.This was the binder formulation widely used on the 1960-70's big boosters...

). The addition of barium nitrate to thermite increases its thermal effect, produces a larger flame, and significantly reduces the ignition temperature. Although the primary purpose of Thermate-TH3 by the armed forces is as an incendiary anti-materiel weapon, it also has uses in welding together metal components.

A classic military use for thermite is disabling artillery
Artillery
Originally applied to any group of infantry primarily armed with projectile weapons, artillery has over time become limited in meaning to refer only to those engines of war that operate by projection of munitions far beyond the range of effect of personal weapons...

 pieces, and it has been used for this purpose during and since World War II; such as at Pointe du Hoc
Pointe du Hoc
Pointe du Hoc is a clifftop location on the coast of Normandy in northern France. It lies 4 miles west of Omaha Beach, and stands on 100 ft tall cliffs overlooking the sea...

, Normandy
Normandy
Normandy is a geographical region corresponding to the former Duchy of Normandy. It is in France.The continental territory covers 30,627 km² and forms the preponderant part of Normandy and roughly 5% of the territory of France. It is divided for administrative purposes into two régions:...

. Thermite can permanently disable artillery pieces without the use of explosive charges, and therefore thermite can be used when silence is necessary to an operation. There are several ways to do this. By far the most destructive method is to weld the weapon shut by inserting one or more armed thermite grenades into the breech
Breech-loading weapon
A breech-loading weapon is a firearm in which the cartridge or shell is inserted or loaded into a chamber integral to the rear portion of a barrel....

 and then quickly closing it. This makes the weapon impossible to be loaded. An alternative method is to insert an armed thermite grenade down the muzzle of the artillery piece, fouling the barrel and making the weapon very dangerous to fire. Yet another method is to use thermite to weld the traversing and elevation mechanism of the weapon, making it impossible to aim properly.

Thermite was also used in both German and Allied incendiary bombs during World War II. Incendiary bombs usually consisted of dozens of thin thermite-filled canisters (bomblets) ignited by a magnesium fuse. Incendiary bombs destroyed entire cities due to the raging fires that resulted from their use. Cities that primarily consisted of wooden buildings were especially susceptible. These incendiary bombs were utilized primarily during nighttime air raids. Bombsights could not be used at night, creating the need to use munitions that could destroy targets without the need for precision placement.

Hazards

Thermite usage is hazardous due to the extremely high temperatures produced and the extreme difficulty in smothering a reaction once initiated. Small streams of molten iron released in the reaction can travel considerable distances and may melt through metal containers, igniting their contents (see images). Additionally, flammable metals with relatively low boiling points such as zinc (with a boiling point of 907 °C (1,664.6 °F), which is about 1370 °C (2,498 °F) below the temperature at which thermite burns) could potentially spray superheated boiling metal violently into the air if near a thermite reaction.

Preheating of thermite before ignition can easily be done accidentally, for example by pouring a new pile of thermite over a hot, recently-ignited pile of thermite slag
Slag
Slag is a partially vitreous by-product of smelting ore to separate the metal fraction from the unwanted fraction. It can usually be considered to be a mixture of metal oxides and silicon dioxide. However, slags can contain metal sulfides and metal atoms in the elemental form...

. When ignited, preheated thermite can burn almost instantaneously, releasing light and heat energy at a much higher rate than normal and causing burns and eye damage at what would normally be a reasonably safe distance.

The thermite reaction can take place accidentally in industrial locations where abrasive grinding and cutting wheels
Grinding wheel
A grinding wheel is an expendable wheel that is composed of an abrasive compound used for various grinding and abrasive machining operations...

 are used with ferrous metals. Using aluminium in this situation produces a mixture of oxides which is capable of a violent explosive reaction.

Mixing water with thermite or pouring water onto burning thermite can cause a steam explosion
Steam explosion
A steam explosion is a violent boiling or flashing of water into steam, occurring when water is either superheated, rapidly heated by fine hot debris produced within it, or the interaction of molten metals A steam explosion (also called a littoral explosion, or fuel-coolant interaction, FCI) is a...

, spraying hot fragments in all directions.

Thermite's main ingredients were also utilized for their individual qualities, specifically reflectivity and heat insulation, in a paint coating or dope
Aircraft dope
thumb|right|[[United Kingdom military aircraft serials|2699]] a [[World War I]] [[Royal Aircraft Factory B.E.2]] finished in a clear dopeAircraft dope is a plasticised lacquer that is applied to fabric-covered aircraft...

 for the German zeppelin
Zeppelin
A Zeppelin is a type of rigid airship pioneered by the German Count Ferdinand von Zeppelin in the early 20th century. It was based on designs he had outlined in 1874 and detailed in 1893. His plans were reviewed by committee in 1894 and patented in the United States on 14 March 1899...

 Hindenburg
LZ 129 Hindenburg
LZ 129 Hindenburg was a large German commercial passenger-carrying rigid airship, the lead ship of the Hindenburg class, the longest class of flying machine and the largest airship by envelope volume...

, possibly contributing to its fiery destruction. This was a theory put forward by the former NASA
NASA
The National Aeronautics and Space Administration is the agency of the United States government that is responsible for the nation's civilian space program and for aeronautics and aerospace research...

 scientist Addison Bain
Addison Bain
Addison Bain is a retired NASA scientist and founding member of the National Hydrogen Association who is credited with postulating the Incendiary-Paint Theory , which posits that the Hindenburg disaster was caused by the electrical ignition of lacquer- and metal-based paints used on the outer hull...

, and later tested in small scale by the scientific reality-TV show MythBusters
MythBusters
MythBusters is a science entertainment TV program created and produced by Beyond Television Productions for the Discovery Channel. The series is screened by numerous international broadcasters, including Discovery Channel Australia, Discovery Channel Latin America, Discovery Channel Canada, Quest...

 with semi-inconclusive results. (It was not proven to be the fault of the thermite reaction, but instead it was conjectured to be a combination of that and the burning of hydrogen
Hydrogen
Hydrogen is the chemical element with atomic number 1. It is represented by the symbol H. With an average atomic weight of , hydrogen is the lightest and most abundant chemical element, constituting roughly 75% of the Universe's chemical elemental mass. Stars in the main sequence are mainly...

 gas that filled the body of the Hindenburg). The MythBusters program also tested the veracity of a video found on the Internet, whereby a quantity of thermite was allowed to drop onto a block of ice of similar mass, causing a sudden explosion. They were able to confirm the results, and Jamie Hyneman
Jamie Hyneman
James Franklin "Jamie" Hyneman is an American special effects expert, best known for being the co-host of the television series MythBusters. He is also the owner of M5 Industries, the special effects workshop where MythBusters is filmed...

 conjectured this was due to the thermite mixture aerosol
Aerosol
Technically, an aerosol is a suspension of fine solid particles or liquid droplets in a gas. Examples are clouds, and air pollution such as smog and smoke. In general conversation, aerosol usually refers to an aerosol spray can or the output of such a can...

izing, perhaps in a cloud of steam, causing it to burn even faster. They found chunks of ice as far as 150 feet (45.7 m) from the point of explosion. Mr. Hyneman voiced skepticism about another theory explaining the phenomenon: one that the reaction somehow separated the hydrogen and oxygen in the water and then ignited them.

See also

  • ALICE (propellant)
    ALICE (propellant)
    ALICE is a rocket propellant which consists of nanoaluminum powder and water. After mixing, the material is frozen to keep it stable. Hence, the name ALICE, for ALuminum ICE rocket propellant.-References:* * * * * -External links:...

  • Ames process
    Ames process
    The Ames process is a process by which pure uranium metal is obtained. It can be achieved by mixing any of the uranium halides with magnesium metal powder or aluminium metal powder.- History :...

  • Chemical reaction
    Chemical reaction
    A chemical reaction is a process that leads to the transformation of one set of chemical substances to another. Chemical reactions can be either spontaneous, requiring no input of energy, or non-spontaneous, typically following the input of some type of energy, such as heat, light or electricity...

  • Exothermic reaction
    Exothermic reaction
    An exothermic reaction is a chemical reaction that releases energy in the form of light or heat. It is the opposite of an endothermic reaction. Expressed in a chemical equation:-Overview:...

  • Exothermic welding
  • Nano-thermite
  • Pyrotechnic composition
    Pyrotechnic composition
    A pyrotechnic composition is a substance or mixture of substances designed to produce an effect by heat, light, sound, gas or smoke or a combination of these, as a result of non-detonative self-sustaining exothermic chemical reactions...

  • Thermate
    Thermate
    Thermate is a variation of thermite and is an incendiary pyrotechnic composition that can generate short bursts of very high temperatures focused on a small area for a short period of time. It is used primarily in incendiary grenades....


External links

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