Chemical reactions at detonation fronts in solids

Abstract

Detonation fronts propagate too fast for the chemical reactions that drive them to be thermally activated. It is proposed that the compression in such fronts causes local metallization when either the density, or the bending of covalent bonds, reaches a critical level which can be estimated from simple models. In the case of the density, this can be estimated from the Herzfeld-Mott model; and in the case of bond-bending, from parabolic variation of the LUMO and HOMO molecular energy levels. Adiabatic expansion of the delocalized electrons provides the high pressure needed to accelerate the ions in the front. Specific examples that are discussed are lead azide, ammonium ions, and nitrate ions. In addition it is argued that this approach is consistent with: observed critical compressions; detonation velocities; the resonance energies of chemical bonds, polarizabilities and the stabilities of energetic materials. Metallization explains why hyper-fast reactions can occur athermally, and propagate supersonically.