Laser initiation of low-density mixtures of PETN with metal additives

This paper presents data on laser initiation of low-density mixtures of PETN with metal additives with varying dispersity of PETN and particle size of the additive. A laser with a wavelength of 1.06 μm and a pulse length of 40 and 30 ns was used. Curves of the threshold initiation parameters on the additive content are shown to have minima. For coarse additives, no significant dependence of the initiation threshold of the mixtures on the nature of the metal at its optimal content (except for aluminum) was observed. For PETN mixtures with an optimal amount of fine aluminum, a significantly greater (a factor of 6.2) decrease in the threshold initiation parameters compared to direct initiation of PETN was found. It is shown that the initiation thresholds of the mixtures do not depend on the dispersity of PETN with the optimal additive content. Increasing the dispersity of PETN extends the dependences of the threshold parameters on the additive content while the optimal additive content is shifted to higher values. The initiation thresholds are found to strongly depend on the density of the mixture charge. The key points of the mechanism of laser initiation of PETN mixtures with additives are formulated.     

Initiating Aluminized High Explosives by Laser Radiation

A number of physical and chemical processes occurring under the action of a laser pulse in nanosized aluminum and aluminized explosives on the basis of fine-grained PETN and benzotrifuroxane along with estimates of the effect of aluminum of the explosive transformation dynamics in these explosives conclude that it is possible to initiate aluminized explosives by laser radiation. The estimated and experimental results show that the main source of hot spots capable of causing an explosive transformation in aluminized explosives under the action of a laser pulse can be a compression wave that forms as a result of rapid evaporation of a sufficient number of aluminum particles. It is shown experimentally that aluminized explosives based on fine-grained RDX and HMX can be initiated by a laser pulse whose source is no more powerful than that in the case of PETN and benzotrifuroxane.     

Effect of multiple scattering on the critical density of the energy used to initiate a PETN–aluminum compound by a neodymium laser pulse

The radiative transfer equation and the Mie theory are used in this paper to determine the optical properties of PETN–aluminum nanoparticles compounds. In the case of laser initiation with a wavelength of 1064 nm, the illumination gain at a depth of 100 μm from the surface of the sample varies in the range of 1.070–3.308 for nanoparticles with radii of 20–200 nm. The minimum of the relationship between the density of the energy required to initiate an explosive decomposition and the mass fraction of nanoparticles can be determined by the maximum illumination gain in the sample. The relationships between the critical density of the energy required to initiate PETN–aluminum nanoparticles compounds by the pulses of the first and second harmonics of a neodymium laser and the nanoparticle radius with account for multiple light scattering are determined. It is shown that account for multiple light scattering improves the agreement between theory and experiment.     

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.     

Influence of the mass fraction of oxide in aluminum nanoparticles on the explosive decomposition threshold and light absorption efficiency in PETN-based compounds

Pulsed laser initiation is used to experimentally investigate the thresholds of explosive decomposition of PETN-based compounds with aluminum nanoparticle inclusions depending on the core-shell (Al/Al₂O₃) mass ratio in the particle. It is found that, with decreasing mass fraction of Al from 74 to 13%, the explosive decomposition threshold increases by a factor of 12.5. Light absorption efficiency calculations for the core-shell system performed by the Aden-Kerker method for Al/Al₂O₃ inclusions in PETN show that this efficiency decreases with decreasing mass of metal in the particle. The experimental and theoretical results can be regarded as an additional confirmation of the hot-spot concept of laser initiation of PETN containing nanoscale inclusions of metals.     

Initiation of PETN explosion by the second harmonic pulse of a neodymium laser

The explosion of PETN of density 1.73 g/cm³ was first initiated by the second-harmonic pulse of a Q-switched neodymium laser. It is shown that the primary process of energy absorption in this case is PETN molecule ionization involving two-photon absorption. The critical initiation energy density corresponding to a 50-% probability of explosion is 12.3 J/cm².     

Laser initiation of PETN-based composites with additives of ultrafine aluminium particles

This paper describes the study on the dependence of the critical energy density of the explosive decomposition of PETN on the mass concentration of the additives of ultrafine Al particles (100–120 nm) in the range of 0.025–1% under the influence of the first and second harmonics of a neodymium laser (12 ns, 1064 and 532 nm). It is shown that the critical energy of the explosion initiation by the first and second harmonics of the laser radiation reaches a minimum value at the same absorption rates, but different concentrations of additives. The photoacoustic method is used to show that, as the laser energy radiation is absorbed, the pressure amplitude in the heated layer reaches a maximum value when the concentration of additives corresponds to the minimum value of the critical energy density.     

Laser initiation of compositions based on PETN with submicron coal particles

This paper describes the results of experiments on laser initiation of composites based on PETN and inclusions of submicron coal particles. The thresholds and kinetic characteristics of explosion of mixed compositions based on PETN and inclusions of submicron coal particles (brown coal B and parabituminous coal P) are studied under the impact of neodymium laser (1064 nm; 12 ns), depending on the mass concentration of inclusions in the range of 0–5%. It is shown that the minimum threshold of explosive decomposition of PETN equal to 1.1 J/cm² can be achieved if the concentration of both types of inclusions is 0.5%.     

Critical conditions of reaction initiation in the PETN during laser heating of light-absorbing nanoparticles

This paper describes the micro-hotspot model of laser initiation of energy materials. The relationship of the critical energy density and the temperature of the reaction hotspot in PETN with the nanoparticle radii of 12 metals at a pulse duration at half-height of 14 ns is determined. It is established that, as the nanoparticle radius is about 10 nm, the critical energy density tends to a certain value independent of heat capacity of metal. This is due to the reduction of the ratio of the nanoparticle volume to the volume of the heated PETN layer, which leads to the fact that most of the energy is spent on heating the matrix. It is shown that the critical hotspot temperature depends on both pulse duration and nanoparticle radius. The analytical expressions for the relationships of the critical parameters of reaction initiation with the radius and heat capacity of metal nanoparticles and for the relationship of the critical hotspot temperature with pulse duration are obtained. The invariant binding the critical energy density and the characteristic development time of the reaction is discovered. The results of this paper are necessary for the optimization of the composition of the optical detonator cell.     

掺杂和密闭透窗对炸药激光起爆感度的影响

用Bruccton法测定了掺杂碳黑和碳纳米管的RDX和PETN炸药的起爆阈值,同时比较了K9玻璃和蓝宝石两种玻璃透窗下激光起爆感度的区别,以及自由振荡和调Q两种激光模式对RDX和PETN起爆感度的影响.结果表明,掺杂碳黑和碳纳米管均可提高RDX和PETN的感度,碳黑的掺杂效果好于碳纳米管,其中掺杂质量分数1%碳黑的RD...     

Simulation of initiation of PETN by a nanosecond laser pulse in the weak absorption region

A numerical simulation of the initiation of PETN by a laser pulse was performed. The heat-conduction equation was solved in a cylindrical coordinate system taking into account multiple reflection of the light beam, zero-order exothermic reaction, and melting. A criterion for the ignition of explosives by a laser pulse with multiple reflection of the light flow was obtained. The calculation results are in satisfactory agreement with experiment and the ignition criterion. Dependence of the critical energy density on the light beam radius is due to radial heat transfer. The ignition threshold can be controlled by changing the reflection coefficient of the back surface of the sample.     

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.     

Conditions of Millisecond Laser Ignition and Thermostability for Ammonium Perchlorate/Aluminum Mixtures

The experimental investigations of laser‐induced ignition and heat action of ammonium perchlorate and aluminum powder mixtures are presented in this paper. A laser pulse with wavelength of 1.06 μm and duration of 3.5 ms was used. Powder mixtures of different dispersion were tested, namely, coarsely dispersed powders and nanopowders with average surface diameters of 80 and 0.25 μm, respectively. The values of ignition thresholds and delays of the mixtures activity in air were measured, and experimental results for different exposure conditions were obtained. The possible reasons of different sensitivity for the given mixtures to laser pulse and heat action are discussed.     

Sublimation Properties of Pentaerythritol Tetranitrate Single Crystals Doped with Its Homologs

Pentaerythritol tetranitrate (PETN) is a secondary explosive used extensively in military and commercial applications. Coarsening of PETN during long‐term storage changes the physical properties such as surface area and particle morphology which are important factors in initiation and performance. Doping of impurities was proposed to slow the coarsening process since impurities were shown to modify both the kinetic and thermodynamic properties. In this paper, we discuss how doping of PETN with its homologs of dipentaerythritol hexanitrate (diPEHN) and tripentaerytritol octanitrate (triPEON) affect kinetic and thermodynamic parameters. Pure and homolog doped PETN single crystals were prepared by solvent evaporation in acetone at room temperature. Doping concentrations for this study were 1000 ppm, 5000 ppm, and 10000 ppm. Activation energy and vapor pressure of pure and doped PETN single crystals were obtained from thermogravimetric analysis data.     

Laser initiation of crystallized mixtures of furazanotetrazine dioxide and dinitrodiazapentane

Experiments were performed to determine the threshold laser pulse energy density resulting in explosive transformation of the mixtures studied. The experiments showed the possibility of using the laser initiation technique for rapid testing of mixtures of variable composition and structure.     

Effect of ultrafine Al-C particle additives on the PETN sensitivity to radiation exposure

The thresholds of explosive decomposition of PETN (pentaerythrite tetranitrate) with the addition of ultrafine Al-C mechanocomposite particles were measured as a function of the concentration of the latter in the experimental samples exposed to laser pulses (1.064 nm, 12 ns). The sample density was 1.73 g/cm³, and the Al-C particle size at the distribution peak was 220 nm. The minimum threshold of explosive transformation corresponding to a 50% probability of explosion with an energy density of 4 J/cm² was reached at an optimum concentration of the mechanocomposite of 0.1–0.3%. Comparison with experimental data obtained for samples with aluminum nanoparticle additives was performed.     

Strength of Commercial Explosives

Strength is determined for mixtures of Amatol (79/21 AN/TNT) with various additives and mixtures of ammonium nitrate and aluminum of various compositions. The results obtained and literature data are used to obtain a formula for calculating the relative strength of commercial explosives containing two parameters — explosion heat and volume of explosion products. The strength of mixtures of ammonium nitrate and aluminum (under powerful initiation leading to overcompressed detonation) exceeds the strength of the reference explosive (Amatol) when the aluminum content is 10—40%. In this case, maximum strength is observed for a mixture containing 30% aluminum. The experimental results and calculations using the proposed formula are in satisfactory agreement.     

Effect of melting on the critical ignition energy of condensed explosives by a short laser pulse

A criterion for the initiation of explosives with a melting point below the ignition temperature by a short laser pulse is obtained. The criterion obtained is in good agreement with numerical solutions of the heat conduction equation in the cylindrical coordinate system. This criterion made it possible to explain experiments on the initiation of PETN from an open surface by a laser pulse in the range of transparency with variation in the diameter of the light beam. The calculation results coincided with the experiment at α = 0.065 cm^?1 and the Fresnel reflection coefficient.     

Simulation of the ignition of organic explosives by a laser pulse in the weak absorption region

Numerical simulation of the ignition of RDX, HMX, and TATB by a nanosecond laser pulse was performed. The heat-conduction equation was solved in cylindrical coordinates with allowance for the multiple reflection of the light beam, a zero-order exothermic reaction, and melting. Despite the small temperature gradient due to the smallness of the radiation absorption coefficient, violation of thermal equilibrium due to Arrhenius nonlinearity leads to ignition of energetic materials from the surface. The critical energy density for ignition of PETN, RDX, HMX, and TATB by a nanosecond laser pulse was determined. Calculations have shown that with identical absorption and reflection coefficients, PETN is the most sensitive and TATB is the most heat-resistant.     

Multi‐Layer Fragment Arresting Jacket for High Density PETN Pressing Operation

Safety is one of the main concerns while pressing high explosives. Many initiating devices consist of a pentaerythritol tetranitrate (PETN) high density column, which is pressed manually in a pneumatic press using a die–plunger assembly. An accidental initiation of the pellet while pressing may lead to severe damages to the press and injuries to the operator. In this paper, a multi‐layer jacket is proposed to be used around the die–plunger assembly during pressing to absorb the energy released by PETN, reduce the shock pressure and arrest fragments in case of an accidental initiation/explosion. The design is based on the stress–strain characteristics of the materials and impedance mismatch principle.