The Surface Explosion of Pyrotechnic Mixtures

Dr Takeo Shimizu


In the past we sometimes observed a fairly large burning star caused an explosion with a loud noise at the very moment when it fell onto the ground. The star did not explode totally, but only with the thin surface layer. The burning surface layer of the star may be very sensitive to shock because of the high temperature. This phenomenon is here called the “surface explosion.” The objective of this paper is to investigate the surface explosion by experiments. It may be very important to make clear the mechanism of the transition from burning to explosion or detonation not only with pyrotechnic mixtures, but also with general explosives, especially to avoid accidents. The mechanical sensitivity of the burning surface layer was examined by dropping an iron ball onto it with consolidated mixtures of ordinary stars and illuminants, etc. Most of them showed a higher sensitivity than that of a standard mixture called red explosive at ordinary temperatures. Using small rocket engines, propellant of potassium chlorate and potassium perchlorate comparing with that of ammonium perchlorate were examined. The former two caused the surface explosion or a perfect detonation when ignited and the rocket engines were broken, and only the propellant of ammonium perchlorate worked well. The phenomenon of the surface explosion was discussed in combination with a past accident.


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