V. G. Kriger

Effect of laser radiation absorption efficiency on the heating temperature of inclusions in transparent media

The efficiency of light absorption by inclusions of various metals in transparent media is calculated using as an example silver azide, lead, and PETN. It is shown that the absorption efficiency, along with the laser pulse energy density, has a decisive influence on the maximum temperature of heating of the inclusion. Dependences of the maximum heating temperature on the radius of the inclusions are plotted for a pulse duration of 30 ns. Asymptotic expressions are obtained for the dependence of the maximum heating temperature on the pulse duration for an ensemble of inclusions.

Influence of laser wavelength on the critical energy density for initiation of energetic materials

Critical densities of the energy of laser initiation of PETN containing nanoscale aluminum inclusions at radiation wavelengths of 1064 and 532 nm were measured experimentally. The critical initiation-energy density that corresponds to a 50%th probability of explosion was 1.15 J/cm2 for the first harmonic of a neodymium laser and 0.7 J/cm2 for the second. The dependence of the efficiency of radiation absorption by aluminum on the size of metal nanoparticles for the first and second harmonics of a neodymium laser is calculated. It is shown that the particle diameter corresponding to the absorption efficiency maximum and the amplitude of the maximum depend on the radiation wavelength. The absorption efficiency maximum for the first harmonic is observed in an inclusion 204 nm in diameter, and for the second, in an inclusion 96 nm in diameter. The amplitude of the maximum increases from 0.351 at a wavelength of 1064 nm to 0.490 at a wavelength of 532 nm. Dependences of the critical initiation energy density for energetic materials on the radius of metallic nanoparticles are calculated. Qualitative agreement between theoretical and experimental results is shown.

Determining the width of the reaction wave front in the explosive decomposition of silver azide

A procedure was developed and used to determine the width of the reaction wave in the explosive decomposition of single crystal whiskers (υ = 1.2 ± 0.2 km/s and l = 230 ± 30 µm) and a pressed powder (υ = 4.0 ± 0.4 km/s and l = 110 ± 10 µm) of silver azide. It is shown that in the mode of reaction propagation at a rate of 1.2 ± 0.2 km/s, the decomposition wave is almost symmetric, in contrast to the detonation wave.

Heat-transfer processes upon laser heating of inert-matrix-hosted inclusions

A model to describe the heating of metal inclusions in inert media by a laser radiation pulse with allowance for the heat-transfer and melting processes in the matrix and inclusion materials is proposed. The time regularities of the heating of the matrix and inclusions were examined, and the dependences of the maximum temperature on the particle surface on the laser pulse energy density and on the particle radius were obtained. Approximate formulae for the maximum heating temperature and for the radius of most heated particles are proposed. We show that melting processes result in a reduction of the maximum heating temperature and in an insignificant variation of the radius of most heated particles.

Miro-hotspot model for the laser initiation of explosive decomposition of energetic materials with melting taken into account

In this paper, we study a micro-hotspot model for the laser initiation of explosive decomposition taking into account the melting of the matrix of the energetic material and the nanometallic inclusion contained in its volume. The heating features of the nanoparticle in an inert matrix are investigated, and the dependence of the maximum temperature on the surface of the inclusion on its radius is constructed. It is shown that melting leads to a reduction in the maximum heating temperature and a slight change in the radius of the most heated nanoparticle. The dependences of the critical initiation energy density of explosive decomposition of pentaerythritol tetranitrate (PETN) with aluminum nanoparticles on the inclusion radius with and without melting are calculated. With melting taken into account, the model gives higher critical initiation energy density of explosive decomposition. In the case of inclusions of large radius, the formation of the reaction site of explosive decomposition occurs before complete melting of the metal inclusion, which results in solidification of the melt during the induction period.

A diffusion model of chain-branching reaction of the explosive decomposition of heavy metal azides

A diffusion model of a solid-phase chain reaction of explosive decomposition of heavy metal azides was developed. The dimensional effects of initiation of the reaction were examined: the dependence of the critical fluence of initiation on the microcrystal size H(R) and on the irradiated zone diameter H(d). It was demonstrated that the diffusion model of the chain reaction closely describes the measured H(R) dependence at diffusion coefficients of D ∼ 0.2–0.3 cm2/s, values that correspond to experimentally measured mobility of electronic charge carriers of μ ∼ 10 cm2/(V s). To account for the measured H(d) dependence and the reaction front propagation velocity (V = 1.2 km/s), it is necessary that the diffusion coefficient be three orders of magnitude higher than the experimentally determined value. That the H(R) and H(d) dependences cannot be quantitatively described simultaneously is indicative of the underlying mechanisms of energy transfer being different.

Rate constant of capture of electron charge carriers on a screened repulsive center

The rate constant of capture of electron charge carriers on a screened repulsive center are performed. Approximate expressions for the potential barrier width, the capture cross section, and rate constant are derived. It is shown that the increase in the concentration of free charge carriers in silver azide from 1016 to 1020 cm−3 results in an increase in the capture rate constant by four orders of magnitude. It is also shown that, with increasing concentration of free carriers, the temperature dependence of the rate constant weakens and the effective activation energy of capture in silver azide decreases from 0.18 to 0.01 eV.

Relaxation of electronically excited products of solid-state reactions in the crystal lattice

The mechanisms of deactivation of electronically excited products of decomposition of silver azide (nitrogen molecules) are examined. A model of dipole interaction with the electron subsystem of the crystal is used to estimate the rate constants of deactivation with formation of electron-hole pairs (∼109 s−1) and energy transfer to a band hole (∼10−12 cm3 s−1). The values obtained confirm the basic postulate underlying the models of solid-phase chain reactions: the preferential formation of electronic excitations of the crystal lattice during the deactivation of excited decomposition products.

Determination of spatial characteristics of the chain reaction wave in silver azide

The paper presents the methodology and results of determination of the spatiotemporal characteristics of the solid-state chain reaction wave in silver azide, initiated by a neodymium laser pulsed. The wave’s leading front width at half maximum is l1 = (110 ± 10) μm, the wave’s rear front width at half maximum is l2 = (120 ± 20) μm. The spatiotemporal parameters of the reaction wave in silver azide whiskers are calculated using a phenomenological model of the process previously proposed by the authors. It is shown that the calculated values of the velocity and the wave front width are consistent with the available experimental data.

Spatial and Temporal Characteristics of Detonation Wave Propagation in Silver Azide

It is shown that a detonation wave is formed in needle-like pressed pellets of silver azide initiated by a neodymium laser pulse. The propagation velocity of the reaction was 3.65±0.12 km/s. Kinetic regularities of the initiation of detonation regimes of propagation of the explosive decomposition reaction were studied, and the spatial characteristics of the glow wave were determined: the width of the leading and rear edges of the wave at half-height were 100±18 and 112±15 µm, respectively.