Supramolecular Structure Influence on Ammonium Nitrate Explosive Properties

Abstract

The ideas regarding the mechanisms of ammonium nitrate (AN) explosive properties occurrence are systematized. It is shown that the AN explosion specific TNT equivalent varies within 0.45–4.0 depending on the accompanying factors set. The AN behavior in the presence of ammonium sulfate and moisture impurities was simulated. It is emphasized that ammonium sulfate can increase the AN explosive properties by releasing a large amount of ammonia in micropores during decomposition, which exacerbates the initiating shock wave pulse as in the Oppau incident case. The moisture role in increasing the AN explosive properties was determined based on the mechanism of wedging water molecules into the crystal lattice: this becomes a dipole barrier that weakens the Coulomb repulsion between nitrate ions, allowing them to come closer together to the point of forming a peroxide bridge under shock wave conditions. Schemes of the AN supramolecular structure for the stable state and for the explosive transformations initiation moment are described with the determination of the detonation susceptibility index KD based on the "melting ease" index. It was established that the scheme "linear cluster based on nitrobasis" gives the detonation tendency index KD > 1, which does not correspond to reality; and for rhombic lattices – KD < 1, which indicates the explosive properties absence. Under the conditions of crystal structure destruction to dimers with a clustering scheme by nitro groups “head-to-head”, KD >1 was obtained, which determines significant explosive properties. The rearrangements model in AN under the shock wave action was developed: the head-to-head AN molecules reorientation of nitrate groups; intermolecular interaction with the nitrogen of a neighboring molecule; nitrate complex formation; the emergence of a bimolecular transition state formation with a peroxide linkage; and dimerization-induced decomposition with the NO2 release and reactive oxygen species, which together initiate the explosion.