Yajuu no skein

Thermite is a pyrotechnic composition of a metal powder and a metal oxide, which produces an aluminothermic reaction known as a thermite reaction. It is not explosive, but can create short bursts of extremely high temperatures focused on a very small area for a short period of time.

Thermites can be a diverse class of compositions. The fuels are often aluminium, magnesium, calcium, titanium, zinc, silicon, and boron. The oxidizers can be boron(III) oxide, silicon(IV) oxide, chromium(III) oxide, manganese(IV) oxide, iron(III) oxide, iron(II,III) oxide, copper(II) oxide, and lead(II,II,IV) oxide. The most common thermite is aluminium-iron(III) oxide.

Although the reactants are stable at room temperature, they burn with an extremely intense exothermic reaction when they are heated to ignition temperature. The products emerge as liquids due to the high temperatures reached (up to 2500 °C (4500 °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 extinguished with water. Small amounts of water will boil before reaching the reaction. If thermite is ignited underwater, the molten iron produced will extract oxygen from water and generate hydrogen gas in a single-replacement reaction. This gas may, in turn, burn by combining with oxygen in the air.

Thermite usage is hazardous due to the extremely high temperatures produced and the extreme difficulty in smothering a reaction once initiated. The thermite reaction releases dangerous ultra-violet (UV) light requiring that the reaction not be viewed directly, or that special eye protection (for example, a welder's mask) be worn. Small streams of molten iron released in the reaction can travel considerable distances and may melt through metal containers, igniting their contents. Additionally, flammable metals with relatively low boiling points such as zinc, whose boiling point of 907 °C (1665 °F) is about 1370 °C (2500 °F) below the temperature at which thermite burns, could potentially boil superheated metal violently into the air if near a thermite reaction, where it could then burst into flame as it is exposed to oxygen.

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. When ignited, preheated thermite can burn almost instantaneously, releasing a much greater amount of light and heat energy 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 are used with ferrous metals. Using aluminium in this situation produces an 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, 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 for the Hindenburg, possibly contributing to its fiery destruction. This was a theory put forward by former NASA scientist Addison Bain, and later tested in small scale by the reality science television show MythBusters with semi-inconclusive results (it wasn't proven to be the thermite reaction's fault but instead was conjectured to be a mix between that and the hydrogen filling the Hindenburg). The Mythbusters also tested the veracity of a video found on the Internet, whereby a quantity of thermite was allowed to drip onto a block of ice of similar mass, causing a sudden explosion. They were able to confirm the results, and Jamie Hyneman conjectured this was due to the extreme temperature difference causing the ice to rapidly sublimate to steam. They also found chunks of ice as far as 150 feet from the point of explosion.