Detonation
Definition and meaning of Detonation in chemistry.
Detonation is an explosive chemical reaction that propagates through a material as a supersonic shock wave, with the heat released by the reaction continuously driving the shock forward. It is the fastest and most destructive mode by which chemical energy can be released from an explosive.
In more detail
The leading shock front compresses and adiabatically heats the unreacted material to the point of near-instantaneous reaction, and the energy this releases sustains the shock, so the reaction zone and shock wave travel together. This contrasts with deflagration, where the reaction front moves subsonically because it spreads by ordinary heat conduction and diffusion rather than shock compression. Detonation velocities and pressures are described by Chapman-Jouguet (C-J) theory, which treats the reaction zone as a discontinuity moving at the unique speed where the products just reach sonic velocity relative to the front. Understanding detonation is essential for explosives safety, engine knock prevention, and industrial blast design.
Key facts
| Field | Physical Chemistry |
|---|---|
| Typical propagation speed | 1,500–9,000 m/s (supersonic) |
| Governing model | Chapman-Jouguet (C-J) theory |
| Contrasts with | Deflagration (subsonic, heat-conduction driven) |
Detonating TNT (trinitrotoluene) generates a shock wave traveling through the solid at roughly 6,900 m/s, converting it almost instantly into hot, high-pressure gaseous products.
Frequently asked questions
What is the difference between detonation and deflagration?
Detonation propagates faster than the speed of sound in the material via a shock wave that compresses and ignites fuel ahead of it; deflagration propagates slower than sound as a flame front spreading by heat conduction and molecular diffusion.
What causes a detonation to start?
An initiating shock, typically from a detonator or from a deflagration accelerating until it transitions ('deflagration-to-detonation transition'), compresses the explosive enough to trigger self-sustaining shock-driven reaction.