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An explosion is an oxidation or a decay reaction with sudden rise of the temperature and the pressure. It comes to a sudden volumetric expansion of gases and the release of large energy quantities on small area, for example by explosives, combustible atmosphere or accumulated gases for instance in volcanos. The sudden volume extension causes a pressure wave, which can be described with an ideal (of a source of point outgoing) explosion by the model of the detonation wave.

The term explosion is used occasionally also for a rapid increase of any size of (e.g. population, costs).

Distinctions

Explosion types

One differentiates two types from explosions: Heat explosions and chain bypass explosions.

  • Heat explosions develop, if the reaction enthalpy cannot be exhausted fast enough and so that the temperature of the system rises. The temperature rise finally leads to a rise of the reaction rate and thus to still larger heat release and to the explosion. (Theories by Semenov, franc Kamenitzkii and Thomas).
  • Chain bypass explosions develop with radical reactions, like the detonating gas reaction. In a certain temperature and pressure range take place more Kettenverzweigungen than chain abort reactions (by recombination of the radicals), so that the number of radicals and thus the set free reaction enthalpy rise fast and lead to the explosion.

These types differ in the kind of the energy setting free chemical reaction. In both cases however the thermodynamic procedure is the same: The set free energy leads to rapid temperature and pressure increase as well as volumetric expansion, which blow up the surrounding material apart.

Finally there are still explosions, at which no chemical or nuclear reaction takes place, but only an increasing pressure in a firm covering (e.g. gas-rich magma in a volcano or steam explosions) these for bursting brings.

Macroscopically

A further distinction is macroscopically met:

  • Deflagration (e.g. Verpuffungen), with which the propagation speed of the flaming or reaction front is slower than the speed of sound of the respective medium (explosive) and the exhaust clouds against the direction of propagation moves.
  • Detonation, which spreads with supersonic speed and moves with that the exhaust clouds in the direction of propagation.

Effect direction

The opposite direction to the explosion is the implosion; here the reactive medium expands not, but contracted. Since the mechanical work leading to the implosion is carried out over the pressure by the surrounding atmosphere and is not set free by an explosive, is the amount of energy, contrary to which, by the imploding volume and by the site conditions limits for an explosion.

Occurrence

Explosions seem to reaction in nature as exotherms frequently. Often explosions are destructive, one can the energy of an explosion in addition, in the explosive technique with a breakup use.

When igniting the fuel in combustion engines one speaks of a burn and not of an explosion, since due to the small burning speed the characteristic characteristics of an explosion do not go into action.

see also: Explosion limit, explosion prevention, flame copy safety device


Articles in category "Explosion"

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» Explosion
» Explosionskrater
» Explosive right

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