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.     

Initiation of PETN detonation by an impactor and a high-enthalpy gas flow

This paper compares two methods of near-threshold initiation of a loose-packed PETN charge: by impact of a plate and by injection of an intense flow of hot gases into the powder. Synchrotron diagnostics of material density was used. Both methods lead to the development of detonation in about 10 μs, but the nature of initiation differs sharply. Initiation by an impermeable piston involves the formation of a dense plug of compressed material. After some delay, a wave is formed at the front of this plug which initiates chemical reaction and accelerates to normal detonation. For high-enthalpy initiation by a hot gas flow, the compression of the powder is low and the process develops in the gas-permeable material, starting from the stage of rapid convective combustion followed by transition to detonation.     

Measuring the temperature of PETN explosion products with iron inclusions

The spectral-kinetic characteristics of luminescence of PETN with iron nanoparticle inclusions are measured in real time in the case of a laser initiated explosion (the wavelength is 1064 nm, and the pulse duration is 14 ns). During the action of the laser radiation pulse, the luminescence of the samples is observed, and the explosive decomposition occurs in a microsecond time interval. The spectral pyrometry method is used to establish the thermal nature of explosive luminescence. The explosion temperature is estimated to be 3400 ±100 K.     

Initiation of combustion of a gas mixture by an electric explosion of an electrolyte

Initiation of combustion of a stoichiometric propane-oxygen mixture in a bubble located in an electrolyte near a dielectric or metallic wall is performed in experiments. It is demonstrated that combustion in the bubble is initiated by an electric explosion-breakdown of a thin electrolyte layer along the bubble boundary.     

Initiation of detonation in hydrogen—Air mixture by explosion of a spherical TNT charge

Direct initiation of detonation by explosion of a TNT charge in a hydrogen—air mixture is considered. The critical mass of initiating charge is determined numerically using a finite-difference method based on the Godunov scheme, taking into account the real chemical kinetics of combustion of hydrogen in air and the real equation of state for gaseous detonation products of TNT. The applicability of the equation of state of a perfect gas to the detonation products of TNT is considered. The effective value of the exponent of Poisson's adiabat is determined.Moscow. Translated from Fizika Goreniya i Vzryva, Vol. 31, No. 2, pp. 91–95, March–April, 1995.     

Initiation of an explosion of a single bubble and bubble detonation

Interaction of a single chemically active bubble in water with acoustic waves is numerically studied within the framework of the model of a two-dimensional unsteady flow of an ideal compressible medium. The boundaries between the phases are explicitly identified. It is demonstrated that bubble explosion initiation can be determined by the character of bubble deformation. Nonsphericity of deformation and jet formation lead to an explosion even if the bubble does not collapse. The possibility of the bubble explosion in an expansion wave, transfer of detonation from one bubble to another, and, thus, emergence of bubble detonation is demonstrated.     

Studies on second harmonic generation efficiency by a series of chiral polyesters

A series of optically active main‐chain polyesters were synthesized by high‐temperature polycondensation from biphenolic azo chromophores, (2R,3R)‐(+)‐diethyl tartrate and terephthaloyl chloride. The polyesters showed glass transition temperatures in the range of 100–135°C and were thermally stable to 350°C. The second harmonic generation efficiency of the polyesters was studied by the powder method and as thin films with 2‐methyl‐4‐nitroaniline as a reference. The SHG efficiency of the polymers was compared with that of low molecular weight chromophores. The polymers with chiral units showed good second harmonic generation efficiency. The SH signal also showed good temporal stability. © 2003 Wiley Periodicals, Inc. J Appl Polym Sci 11: 2468–2473, 2003     

Optical second harmonic generation in LiNbO3 crystals induced by a photovoltaic grating

Optical second harmonic induced by photovoltaic grating written in LiNbO₃:Fe was observed Harmonic generation was due to the third-order nonlinear coefficient f₃₃₃₃ linearized in the electric field of the grating. The phase matching condition was achieved by a suitable choice of the grating period.     

On the mechanism of ignition of condensed secondary explosives by a laser pulse

A mechanism of laser ignition of secondaryHE is proposed which takes into account the strength characteristics of the material. The formation of microcracks upon heating of an optical microinhomogeneity is considered to be responsible for failure of the ignition process ofHE. UsingPETN as an example, it is shown that the calculation results agree quantitatively with experimental results on the ignition of secondaryHE loaded with external pressure.Translated from Fizika Goreniya i Vzryva, Vol. 32, No. 1, pp. 11–19, January–February, 1996.     

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.     

Initiation of lead azide using an electron pulse

A thermal model of the initiation of lead azide by means of an electronic pulse is studied. The heattransfer equations, which take into account the burnup of the sample, are solved numerically. Equations are derived for the ignition criterion and for the delay times in the ignition of condensed explosive materials. It is shown that the thermal ignition cannot explain the short delay time in the lead azide initiation by means of an electron pulse. Kemerovo. Translated from Fizika Goreniya i Vzryva, Vol. 29, No. 5, pp. 63–66, September–October, 1993.