Optical depth measurements of fireballs from aluminized high explosives

Spatially and temporally resolved attenuation of 532 nm light by fireballs from aluminized high explosives is determined using photometric and imaging methods. For all measurements, the absorbance is found to peak during the early period of high reactivity of post-detonation gases. The characteristic attenuation length is less than 1 cm during the peak absorption period, and remains on the order of centimeters until a significant decrease in optical depth occurs about 160 μs after the detonation. These results suggest that, for gram-scale and larger aluminized charges, the optically thick assumption will most likely be valid for the period in which fireball luminosity is significant.     

Heat of explosion and acceleration ability of aluminized hexanitrohexaazaisowurtzitane-based compositions

Measurements and calculations of the heat of explosion and acceleration ability of aluminized compositions based on hexanitrohexaazaisowurtzitane, a promising high explosive, showed that the indicated parameters of such mixtures substantially exceed those of HMX-based counterparts. Creating aluminized nanocomposites to improve the acceleration ability is advantageous only if the content of the oxide film in the nanoaluminum powder is minimized by coating the particles with a protective layer of an active material. According to calculations, nanocomposites containing hexanitrohexaazaisowurtzitane and aluminum with active coating should have a record acceleration ability.     

Effect of the Al/O ratio on the Al reaction of aluminized RDX-based explosives

Aluminum(Al) powders are used in composite explosives as a typical reducing agent for improving explosion performance. To understand energy release of aluminum in aluminized RDX-based explosives, a series of thermal measurements and underwater explosion(UNDEX) experiments were conducted. Lithium fluoride(LiF) was added in RDX-based explosives, as a replacement of aluminum, and used in constant temperature calorimeter experiments and UNDEXs. The influence of aluminum powder on explosion heat(Qv) was measured. A rich supply of data about aluminum energy release rate was gained. There are other oxides(CO_2, CO, and H_2O) in detonation products besides alumina when the content of RDX is maintained at the same levels. Aluminum cannot fully combine with oxygen in the detonation products. To study the relationship between the explosive formulation and energy release, pressure and impulse signals in underwater experiments were recorded and analyzed after charges were initiated underwater. The shock wave energy(Esk), bubble energy(Eb), and total energy(Et) monotony increase with the Al/O ratio, while the growth rates of the shock wave energy,bubble energy, and total energy become slow.     

Review of the Forest fire model for high explosives

Forest fire is a burn model for reactive hydro simulations that is widely used to describe both initiation and propagation of detonation waves in solid high explosives. Here we thoroughly review the assumptions of the model. In analogy with Whitham–Chisnell shock dynamics, we derive the Forest fire rate based on a characteristic analysis of a shock-to-detonation transition. Code issues with implementing the Forest fire model are also discussed. The analysis leading to the Forest fire rate is more general than the simplifying assumptions used by the model. The Forest fire analysis provides important constraints needed for any burn model to fit shock initiation data. This data is fundamental to ignition sensitivity of high explosives.     

Tendencies in the development of studies of high explosives

An energy-content-based criterion of assessing the detonability of organic HEs is proposed. The energy content of HEs is demonstrated to be a quantitative measure of the detonability, which can be estimated using the chemical composition and enthalpy of formation of the HE.     

Tendencies in the development of studies of high explosives

The state of studies of high explosives is examined. The limiting possibilities of organic high explosives in the detonation velocity, metal acceleration ability, and energy stored are assessed. The prospects of development of research in this field are discussed.     

Microstructure and oxidation of hot-dip aluminized titanium at high temperature

High-temperature diffusion of a hot-dip aluminized titanium is conducted to study microstructure changes and oxidation behavior of the aluminized titanium. After aluminizing, the titanium substrate is covered by a black layer in which tiny block-shaped TiAl₃ particles are scattered in aluminum matrix. Based on the diffusion experiment results, the thickness of the aluminum diffusion layer at 800 °C increases with diffusion time. However, the aluminum diffusion layer at 900 °C grows and reaches its maximum thickness in 6 h, and then the thickness of the aluminum diffusion layer is reduced with prolonged diffusion time. An inversion of the diffusion layer thickness versus time appears for the aluminized titanium treated at 1000 °C, and the thickness of the diffusion layer keeps declining with diffusion time. The phases present in the outer and middle sublayers are titanium-rich TiAl₃ and equilibrium TiAl₃, respectively. However, the phase in inner sublayer changes from titanium-rich TiAl₃ to TiAl₂ and TiAl as diffusion temperature and time increase. Through energy-dispersive X-ray and X-ray diffraction analysis, the oxides formed in the oxidation process are Al₂O₃ and Al₂TiO₅. Although the oxide scale formed on the surface of the aluminized titanium has an insufficient stability and integrity, the thermal oxidation resistance of the aluminized titanium is still improved by over 5 times compared with that of the pure titanium.     

Acceleration ability of high explosives and their mixtures with fuel additives. 1. Assessment by the M-40 method

The relationship between the chemical composition of the detonation products and the acceleration ability of explosives is considered. Based on theoretical and experimental studies, it is concluded that, at volumetric energy content, the most important parameter is the average atomicity of the molecules constituting the detonation products. Among the CHNOF-containing explosives, groups with high acceleration ability were identified. The experimental results on the acceleration ability obtained using the M-40 method are reported for mixtures of dispersed Al with HEs with different oxygen balance and for mixtures of HMX-based HE with Al, Mg, Y, Ta, ZrH₂. An analysis of the acceleration ability on the charge density for BTNEN and mixtures thereof with Al made is possible to estimate the degree of conversion of the energy of combustion of Al under the gasdynamic conditions typical of the M-40 method, which turned out to be 20–40%.     

On the mechanism of the detonation of organic high explosives

This article presents a further analysis of isotopic labeling data on the mechanism of the detonation of TNT-, RDX-, and HMX-containing mixtures and on the release of free carbon from these mixtures. The distribution of carbon isotopes among the condensed explosion products and, for the first time, among the gaseous ones is considered in relation to the particle size of the mixed explosives. A sequence of main chemical reactions in the detonation wave is suggested to account for the experimental data discussed.     

Acceleration ability of high explosives and their mixtures with fuel additives. 2. Activated and ultrafine aluminum powders

The acceleration ability of high explosives containing additives of activated and ultrafine aluminum was considered. It was demonstrated that different methods of activation of Al oxidation that make it possible to increase the rate of this process in air severalfold produce little or no effect on the acceleration ability of aluminized high explosives. The basic features of the behavior of Al in detonation waves that explain the results are formulated.     

Determination of detonation parameters of liquid high explosives

An experimental study of the detonation parameters and structure of the reaction zone for liquid high explosives (HEs), such as bis(2-fluoro-2,2-dinitroethyl)formal (FEFO), tetranitromethane (TNM), and nitromethane (NM) is performed. For each of these HEs, the time corresponding to the position of the Chapman-Jouguet point is determined: for FEFO, from experiments conducted at different charge diameters (≈300 ns); for TNM, at a fixed diameter but at different lengths (≈200 ns); and for NM, at the same diameter and length of the shell, but with detonation being initiated by different HE charge (≈50 ns). The particle velocity and pressure at the Chapman-Jouguet point for these explosives were measured. For TNM and NM, the dependence of the detonation velocity on the charge diameter was obtained     

Acceleration ability of high explosives and their mixtures with fuel additives. 3. Acceleration of steel shells and plates

The process of acceleration of plates and destroyable steel shells is examined. It is shown that 85% of the energy of the secondary reactions in the detonation products is converted into the work of acceleration of the shell. The conclusion is drawn that the incomplete transformation of the potential energy stored in aluminized explosives is associated not so much with a low rate of Al combustion in the detonation products, but rather with the thermodynamic properties of its oxidation and the gas-dynamic conditions under which the work of explosion is done. An important role of the processes occurring at the detonation products-air interface is emphasized. A physical model capable of adequately describing the experimental results is proposed.     

同步辐射照相与凝聚炸药爆轰研究

高能凝聚炸药的爆轰传播规律是爆轰物理学的重要研究内容,它在武器设计与研制中具有重要的应用价值。该文介绍了近年来基于同步辐射X射线照相装置的凝聚炸药爆轰实验无损观测与诊断技术的研究动态,主要内容包括炸药爆轰波阵面及爆轰波后流场实验测试及其诊断技术等。     

Method for estimating coherent properties of radar signals

We propose a method for estimating coherent properties of signals within the framework of the correlation theory. A quantitative measure of coherence is obtained in the form of entropy of the signal energy distribution over the eigensubspaces of the correlation matrix of the signal. Examples are given to illustrate the effectiveness of the obtained measure. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Radiofizika, Vol. 49, No. 1, pp. 82–87, January 2006.     

Estimation of the acceleration ability for electrons in SiO2 and the tunneling effect

Silicon dioxide (SiO₂) plays an important role in layered optimization scheme and solid-state cathodoluminescence (SSCL). Initially, it was believed that the SiO₂ layer would (i) generate extra interface states contributing to a number of primary electrons available for exciting the luminescent centers, and/or (ii) act as acceleration layer resulted in gaining high energy for those electrons that would tunnel into the luminescent layer to excite luminescent centers. Based on the brightness vs. voltage (B-V) measurements, we deem that the latter case, i.e. acceleration and tunneling, is the dominant mechanism. A detailed discussion in terms of electrons acceleration and tunneling as the main contributions to the enhancement of brightness is presented.     

On the initiation of detonation in high explosives by a high-current electron beam

A critical analysis of experimental work on the initiation of high explosives (HE), high-current electron beam of nanosecond duration. It is demonstrated that there is no unambiguous evidence for the initiation of detonation in HE by the electron beams described in the reviewed works. The results of experiments on the effects of a pulsed electron beam on model paraffin samples are presented, which show that the geometric parameters of the sample and the presence of copper oxide nanopowder in it influence its resistance to the action of the beam. It is shown that the main effect on the sample is produced by cathode plasma beam and that the selection of the sample geometry and introduction of nanopowders can enhance the action of a high-current electron beam.     

Experimental study of the relief of the front of steady detonation in liquid high explosives

The instability of detonation waves in a 81 : 19 nitromethane-acetone mixture is experimentally studied. The amplitude of the irregularities caused by detonation instability and the typical reaction time are estimated using a VISAR laser interferometer, which makes it possible to measure the particle velocity profiles at the explosive-window interface. The characteristic transverse dimensions of the irregularities are measured with the help of a CORDIN camera operating in the single shooting mode to record the intrinsic emission of the detonation front or the light of an outside source reflected from it.     

Influence of the particle size of the components on the mechanical sensitivity of metallized high explosives

The results of experimental studies of the mechanical initiation of compositions of explosives (HMX, RDX) with aluminum powder at various component and granulometric compositions are presented. It is shown that nanocomposites and mechanical mixtures of explosives with nanoscale aluminum are characterized by extremely high sensitivity in comparison with compositions containing micron-sized aluminum powder. The results are explained based on the assumption that an increase in the sensitivity is caused by an additional heat release in the course of chemical interaction of components at mechanically induced hot spots. Data on the effect of passivating coating and aging of the particles of nanoscale aluminum on the sensitivity of binary compositions are obtained and analyzed.