A. Yu. Mitrofanov

Role of electronic excitations in explosive decomposition of solids

A combined theoretical and experimental study is performed for the initiation of chemistry process in high explosive crystals from a solid-state physics viewpoint. In particular, we were looking for the relationship between the defect-induced deformation of the electronic structure of solids, electronic excitations, and chemical reactions under shock conditions. Band structure calculations by means of the Hartree–Fock method with correlation corrections were done to model an effect of a strong compression induced by a shock/impact wave on the crystals with and without edge dislocations. Based on the obtained results, an excitonic mechanism of the earliest stages for initiation of high explosive solids is suggested with application to cyclotrimethylene trinitramine (also known as RDX) crystal. Experimental tests of this mechanism for AgN3 decomposition controlled by the dislocation density were worked out. The use of pulse radiolysis techniques allows us to observe pre-explosion modifications in properties...

Laser initiation of PETN in the mode of resonance photoinitiation

The effect of the initial temperature of the sample on the efficiency of laser initiation and on the duration of the preexplosion stage (induction period) of PETN is studied. An analysis of the results leads to the conclusion that, in the initiation of PETN with the first harmonic of a neodymium laser (1060 nm), a new selective resonant mode of photoinitiation is realized, through the formation of active radicals providing the development of a chain reaction of explosive decomposition at the preexplosion (solid-phase) stage of the process. For this mode, the threshold volume density of energy absorbed is much lower than that typical of the traditional non-selective mechanisms of initiation. The mode of resonant photoinitiation is, however, difficult to realize because of a low value of the absorption coefficient in the actual band. This difficulty can be easily overcome by introducing light-scattering additives, a modification that opens prospects for practical use of resonant photoinitiation.

Preexplosion phenomena in heavy metal azides

The paper reports results of investigation of the explosive decomposition of heavy metal azides in real time. The characteristics of the detected predetonation effects — the preexplosion conductance and luminescence of heavy metal azides — are described. The obtained value of the preexplosion conductivity of silver azide indicates that the process is of a chain nature. A model for the development of explosion of heavy metal azides is developed including multiplication of active particles (holes) by a first-order reaction and chain termination by a second-order reaction.

Model of the photostimulated fragmentation of PETN molecules in selective photoinitiation

A model of the photostimulated fragmentation of the PETN molecule irradiated by the first harmonic of a neodymium laser (1060 nm) is proposed. Photoexcitation at 1060 nm leads to the n → π* transition of the 2p nonbinding electron of the oxygen to the π* antibonding orbital, a transition that causes the rupture of the O-N bond and the formation of NO2* radicals, thereby ensuring a further development of explosive decomposition. In the case of a free molecule or a molecule located on the surface of a microcrystal, the process does not require any thermal activation. In the case of a molecule at a regular lattice site, an additional activation energy (0.4 eV) is needed to overcome the potential barrier associated with the passage of through a bottleneck between the nearest-neighbor molecules.

Photo- and thermochemical initiation of PETN under laser excitation

A method for separate control of the efficiencies of the photochemical and thermochemical mechanisms of initiation of energetic materials by laser excitation for a combined action of these mechanisms is proposed. The method is based on the difference in the timescales of the relevant photo- and thermochemical initiation processes, a factor that leads to a different dependence of the efficiencies of these mechanisms on the initiating pulse duration and initiation irradiance. An experimental validation of the method for the initiation of PETN with 1064- and 1070-nm light at irradiances of ∼109 and ∼104 W/cm2, respectively, is performed. The results show that, for the initiation of pure PETN at an irradiance of 109 W/cm2, the photochemical mechanism dominates, ensuring an initiation threshold of ∼4 J/cm2. In the case of samples with light-absorbing inclusions (carbon) and the same irradiance ∼104 W/cm2, only the thermochemical mechanism is operative, with an initiation threshold of ∼15 J/cm2. In the absence of light-absorbing inclusions, the sample does not explode even at a fluence of ∼75 J/cm2; i.e., in this case, the initiation threshold is clearly higher than this value.

Dynamic Topography of Silver Azide Pre‐Explosion Luminescence

For the first time, it is experimentally shown that silver azide pre‐explosion luminescence emerging under weak laser excitation originates and develops locally. As the excitation intensity increases, the mean number of local luminous regions also increases, finally giving rise to homogeneous luminescence.

Explosive luminescence of heavy metal azides

Light emission accompanying the explosive decomposition of heavy metal azides has been investigated. It has been found that predetonation luminescence seems to occur as a result of intraband transitions to a quasilocal state in the valence band.

Photochemical and photothermal dissociation of PETN during laser initiation

The temperature dependence of the efficiency of laser initiation (λ = 1060 nm) of pure PETN with an open and closed surface and PETN with a light-scattering additive (0.5% MgO) and an open surface was studied. It was found that the closing of the surface and introduction of light-scattering additives leads to a change in the temperature dependence of the initiation threshold. The observed effect is associated with the specificity of the photoinduced fragmentation of PETN molecules in defective areas of the crystal lattice.

Kinetics of the Early Stage of Preexplosion Conduction in Silver Azide

Experimental data on the kinetics of preexplosion conduction of silver azide in the early stage of explosive decomposition initiated by a pulse action were obtained for the first time. It is found that the kinetics of conduction in the early stage is more complex than that at later stages. In the early stages, the difference between kinetic curves for various samples is greater than that for the steady process. Key words: silver azide, explosion, chain reactions, conduction, kinetics, pulse photolysis.

Influence of the thickness and absorption coefficient of a copper oxide film on the ignition delay of PENT by a laser pulse

Numerical modeling of PETN ignition by a copper oxide film absorbing laser radiation has been performed. The calculation results showed the presence of a minimum in the curve of the dynamic delay of PETN ignition by a rectangular laser pulse versus thickness of the absorbing film. This effect is due to the fact that when the film thickness is commensurate with the reciprocal of the absorption coefficient, the amount of heat generated in the thin film due to the multiple reflection of the light flux is proportional to its thickness. Therefore, the smaller the film thickness, the more time is required to heat it to the ignition temperature of PETN. In the case of a thick film, additional energy and time are required to heat its cold part to the ignition temperature of PETN.