Initial stage of the explosion of ammonium nitrate and its powder mixtures

Abstract

There is an obvious contradiction between the statistics of the devastating explosions that take place with the participation of ammonium nitrate and explosive properties of this material determined in standard tests. Pure ammonium nitrate does not burn under normal conditions and has a very low sensitivity to conventional mechanical and thermal stimuli. So far, ammonium nitrate has been detonated only by using high explosives. Causes of accidental explosions involving large masses of ammonium nitrate are likely to be found in a nonconventional behavior of ammonium nitrate. These changes may arise due to different chemical or physical factors, such as those associated with the presence of active additives, crushing of particles, etc., and lead to acceleration of the process at the initial stage of explosion. This work is devoted studying the convective burning and the initial stage of deflagration-to-detonation transition in dry and wet mixtures of ammonium nitrate with various, largely combustible additives. Experiments were conducted on loose-packed charges in a constant-volume bomb and by using the method of the critical bed height with recording pressure-time diagrams by a piezoelectric sensor. Ammonium nitrate of two different types was used: granular and powdered. The fuel additives were charcoal and aluminum powder, whereas the additives inhibiting the combustion of ammonium nitrate were water and monosodium salt of phosphoric acid. In addition, finely dispersed mixture of four components (ammonium nitrate, aluminum, powdered sugar, and TNT in a proportion of 76: 8: 12: 4) was used. The experiments in the constant-volume bomb were supplemented by numerical simulations, which made it possible to obtain a better understanding of the convective burning of the test mixtures and to evaluate the possibility of using a constant-volume bomb to collect quantitative information on the intensity of the combustion of the mixture at the initial stage of the explosion.