Editing Explosive (section)

==Types==

===Chemical===
[[File:GHS-pictogram-explos.svg|thumb|The [[Globally Harmonized System of Classification and Labelling of Chemicals|international]] [[GHS hazard pictograms|pictogram]] for explosive substances]]

An explosion is a type of spontaneous chemical reaction that, once initiated, is driven by both a large exothermic change (great release of heat) and a large positive [[entropy]] change (great quantities of gases are released) in going from reactants to products, thereby constituting a thermodynamically favorable process in addition to one that propagates very rapidly. Thus, explosives are substances that contain a large amount of energy stored in [[chemical bond]]s. The energetic stability of the gaseous products and hence their generation comes from the formation of strongly bonded species like carbon monoxide, carbon dioxide, and nitrogen gas, which contain strong double and triple bonds having bond strengths of nearly 1 MJ/mole. Consequently, most commercial explosives are organic compounds containing [[nitro compound|–NO<sub>2</sub>]], [[nitrate|–ONO<sub>2</sub>]] and [[nitroamine|–NHNO<sub>2</sub>]] groups that, when detonated, release gases like the aforementioned (e.g., [[nitroglycerin]], [[trinitrotoluene|TNT]], [[HMX]], [[PETN]], [[nitrocellulose]]).<ref>{{cite book |first=W.W. |last=Porterfield |title=Inorganic Chemistry: A Unified Approach |edition=2nd |publisher=Academic Press, Inc. |location=San Diego |pages=479–480 |date=1993}}</ref>

An explosive is classified as a low or high explosive according to its rate of [[combustion]]: low explosives burn rapidly (or [[deflagration|deflagrate]]), while high explosives [[detonation|detonate]]. While these definitions are distinct, the problem of precisely measuring rapid decomposition makes practical classification of explosives difficult. For a reaction to be classified as a detonation as opposed to just a deflagration, the propagation of the reaction shockwave through the material being tested must be faster than the [[speed of sound]] through that material. The speed of sound through a liquid or solid material is usually orders of magnitude faster than the speed of sound through air or other gases.  

Traditional explosives mechanics is based on the shock-sensitive rapid oxidation of carbon and hydrogen to carbon dioxide, carbon monoxide, and water in the form of steam. [[Nitrate]]s typically provide the required oxygen to burn the carbon and hydrogen fuel. High explosives tend to have the oxygen, carbon, and hydrogen contained in one organic molecule, and less sensitive explosives like ANFO are combinations of fuel (carbon and hydrogen fuel oil) and [[ammonium nitrate]]. A sensitizer such as powdered aluminum may be added to an explosive to increase the energy of the detonation. Once detonated, the nitrogen portion of the explosive formulation emerges as nitrogen gas and toxic [[NOx|nitric oxides]].

====Decomposition====
The [[chemical decomposition]] of an explosive may take years, days, hours, or a fraction of a second. The slower processes of decomposition take place in storage and are of interest only from a stability standpoint. Of more interest are the other two rapid forms besides decomposition: deflagration and detonation.

====Deflagration====
{{Main|Deflagration}}
In deflagration, decomposition of the explosive material is propagated by a flame front which moves relatively slowly through the explosive material, {{em|i.e.}} at speeds less than the speed of sound within the substance (which is usually still higher than 340&nbsp;m/s or {{convert|340|m/s|km/h|-1|disp=out}} in most liquid or solid materials)<ref>{{cite web |url=http://www.chem-page.de/publikationen/geschichte-der-sprengstoffe/195-2-wie-unterscheiden-sich-deflagration-detonation-und-explosion.html |access-date=2017-02-05 |url-status=dead |archive-url=https://web.archive.org/web/20170206104750/http://www.chem-page.de/publikationen/geschichte-der-sprengstoffe/195-2-wie-unterscheiden-sich-deflagration-detonation-und-explosion.html |archive-date=6 February 2017 |df=dmy-all |title=2.1 Deflagration |language=de |website=chem-page.de}}</ref> in contrast to detonation, which occurs at speeds greater than the speed of sound. Deflagration is a characteristic of [[low explosive]] material.

====Detonation====
{{Main|Detonation}}
This term is used to describe an explosive phenomenon whereby the decomposition is [[wave propagation|propagated]] by a [[shock wave]] traversing the explosive material at speeds greater than the speed of sound within the substance.<ref>{{cite web |url=http://www.chem-page.de/publikationen/geschichte-der-sprengstoffe/195-2-wie-unterscheiden-sich-deflagration-detonation-und-explosion.html |title=2.2 Detonation |website=chem-page.de |language=de |access-date=2017-02-05 |url-status=dead |archive-url=https://web.archive.org/web/20170206104750/http://www.chem-page.de/publikationen/geschichte-der-sprengstoffe/195-2-wie-unterscheiden-sich-deflagration-detonation-und-explosion.html |archive-date=6 February 2017 |df=dmy-all }}</ref> The shock front is capable of passing through the high explosive material at supersonic {{nowrap|speeds{{tsp}}{{mdash}}{{tsp}}}}typically thousands of metres per second.

===Exotic===
In addition to chemical explosives, there are a number of more exotic explosive materials and exotic methods of causing explosions. Examples include [[nuclear explosive]]s, and abruptly heating a substance to a [[plasma (physics)|plasma]] state with a high-intensity [[laser]] or [[electric arc]].

Laser- and arc-heating are used in laser detonators, [[exploding-bridgewire detonator]]s, and [[slapper detonator|exploding foil initiators]], where a shock wave and then detonation in conventional chemical explosive material is created by laser- or electric-arc heating. Laser and electric energy are not currently used in practice to generate most of the required energy, but only to initiate reactions.