A. V. Kalenskii

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.

Explosive decomposition of PETN with nanoaluminum additives under the influence of pulsed laser radiation at different wavelengths

The results of measurements of the threshold of explosive decomposition of PETN with 0.1 wt % additives of aluminum nanoparticles under the action of the first and second harmonics of a YAG:Nd3+ laser with a pulse duration of 12 ns are presented. A comparison of experimental and theoretical results is performed. It is concluded that the absorption of radiation heats the nanoparticles to form chemical decomposition kernels in the vicinity of the hotspot, so that the initiation of explosive decomposition is not associated with optical breakdown of the sample.

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.

Explosive decomposition kinetics of tetranitropentaerythrite aluminum pellets

The explosive decomposition kinetics of tetranitropentaerythrite aluminum compressed pellets is studied with a high time resolution. Explosive decomposition is initiated by a pulsed 1064-nm laser with a pulse FWHM of 12 ns. Emphasis is on the prethreshold glow mode, which sets in at a pulse energy density below 1 J/cm2. The ascending part of the glow intensity curve is described by a Gaussian function with effective constant k = (1.2 + 0.2) × 108 s−1. The characteristic decay time is about 40 ns. The total glow duration does not exceed 100 ns. Explosive decomposition becomes noticeable immediately during the pulse: the induction period is absent. The initial portion of the glow intensity curve is described by a Gaussian function with effective constant k = (1.4 + 0.1) × 108 s−1. The explosive glow kinetics is biextremal. The first peak is nearly coincident with the maximum of the laser action, and the extension of the second peak is 600 ns. Experimental data are treated in terms of the prethreshold model of thermal explosion.

Specific Features of Plasmon Resonance in Nanoparticles of Different Metals

Spectral dependences of the light extinction and absorption efficiency coefficients are calculated for silver, gold, nickel, and aluminum nanoparticles within the framework of the Mie theory. It is demonstrated that narrow plasmon bands are observed for small (with a radius of less than 50 nm) nanoparticles of noble metals, whereas broad bands in the spectral dependences of the extinction and absorption efficiencies are typical for nickel and aluminum nanoparticles. It is concluded that using spectral dependences of extinction for estimating the radius of nanoparticles is correct only for noble metals. The results are interpreted based on wavelength dependences of complex refractive indices of metals.

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.