Under the detonation speed of an explosive one designates the speed of the reaction front, with which the chemical reaction moves itself within the explosive, how quickly and suddenly he decomposes or reacts thus. When product of detonation speed, load density and specific energy results the explosiveness Sprengstoffes.Eine large detonation speed ensures for the fact that the pressure build-up is passed suddenly and the energy stored in the chemical compounds is set free in as short a time as possible.
While black powder under formation of large masses of gas burns relatively slowly (with subsonic speed usually of a Deflagration one speaks), becomes explosive explosives with the tenfold speed and more converted. This procedure is called detonation and the reaction front forms a shock wave (see also detonation wave).
Only if a pressure must be developed with slow explosives such as black powders by insulation, which suddenly sets its energy free with blow-out of the insulation then, which is to be heard also as bang, is no longer in principle necessary this with explosives of high detonation speed (higher than the speed of sound). Pressure-more insensitive explosive explosives (for example TNT) are loaded nevertheless into firm casings. Without detonating this covering up to several millimeters a thick external layer of the charge blown off without, which would decrease the efficiency (after Pokrowski, "explosion and breakup").
A short table outlines the typical (maximum) detonation speeds of some well-known explosives (the values can be different depending upon source):
|Explosive designation||Detonation speed|
|Black powder||0.4 km s-1|
|Ethin/oxygen||2.4 km s-1|
|Chloratit 3||3.35 km s-1|
|Lead azide||4.63 km s-1|
|Gun cotton||6.3 km s-1|
|Gel dynamite||6.35 km s-1|
|TNT (trinitrotoluene)||6.7 km s-1 or 7.028 km s-1|
|7.1 km s-1|
|Nitroglycerin||~2.5 km s-1 to 7.7 km of the kind of the ignition and the insulation in some cases even up to 9 km s-1|
|Nitropenta||5 km s-1 to 8.34 km s-1 depending upon load density|
|RDX (Hexogen)||8.4 km s-1|
|HMX (Octogen)||9.11 km s-1|
|CL20 (Hexanitro Isowurtzitan)||9.38 km s-1 or 10.3 km s-1|
The detonation speed can be determined by the procedure by Dautriche. During this procedure the explosive which can be examined is included in a steel tube. In the steel tube are two blasting caps, which have a certain distance from each other. The blasting caps are connected with a detonation cord, which runs parallel to the steel tube by a Bleiplatte. The detonation cord contains usually Pentaerythrit tetranitrat with a constant detonation speed of approx. 7000 m/s. If the explosive in the steel tube is ignited, the progressive detonation releases successively the explosions of the blasting caps. The explosion of the blasting caps reproduces itself at both ends of the Sprengschur. The shock waves of the detonation cord approach one on the other and cause at its meeting place a groove into the Bleiplatte. Due to the fact that a blasting cap detonates in former times, it is the groove never in the center of the cord, but always further right. The further the groove deviates from the center, the detonation speed is the smaller. One computes the looked for detonation speed on the basis the formula Dx = D m a-1, whereby D is the detonation speed of the detonation cord, m the length of the measuring section and A the distance of the groove from the cord center.
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