Imitation of wave processes by generating an electric explosion of conductors in nonuniformly heated materials

A new method for imitating wave processes in nonuniformly heated materials by means of the electroexplosion of conductors was proposed. The problem of a planar high-current discharge initiated by the explosion of a foil in the air was solved in the 1D approximation of magnetic radiation gas dynamics with regard to the dependence of the conductivity of the foil on the density and temperature of the material during electroexplosion, a dependence that characterizes the specifics of the state of the material in various areas of the phase diagram. The main parameters of the electroexplosion setup were selected. A special construction of the loading unit was developed, which eliminates the effect of current contraction in a planar conductor and ensures a uniform distribution of current over the foil and, consequently, a uniform distribution of the pressure pulse momentum over the surface area of loading. A method for imitating the temperature profile in the sample was proposed. A procedure for measuring the integral pressure pulse momentum under conditions of intense electromagnetic disturbances was developed.     

Thermodynamic analysis of gasification of renewable carbonaceous materials of natural and artificial origin in plasma electric furnace

Thermodynamic analysis of plasma gasification of various renewable carbon-bearing materials was carried out using various oxygen-containing oxidants (oxygen, air, water). The possibility of obtaining calorific synthesis gas suitable for the needs of heat power engineering was confirmed.     

Wave dynamics of electric explosion in solids

A mathematical model of an electric explosion is developed that consistently describes the expansion of the explosion channel with regard to the parameters of the discharge circuit of a high-voltage pulse generator, radiation, and propagation of stress waves in a solid. The dynamics of conversion of the stored energy to a wave and the formation of mechanical stresses due to electric explosion in a solid immersed in a liquid are considered. In the context of electro-discharge destruction of hard materials, the resulting stress field and the relationship between the discharge circuit parameters and characteristics of the wave are analyzed and the most efficient discharge modes are determined.     

Skin electric explosion in double-layer conductors with a low-conductivity deposited layer

The experiments on explosion of cylindrical conductors aimed at comparison of plasma formation during skin explosion of homogeneous and double-layer conductors with an external layer with a lower conductivity are carried out on a high-current MIG generator (current amplitude up to 2.5 MA and current rise time 100 ns). The generator is loaded with cylindrical copper conductors with a diameter of 3 mm on the cathode part of which a titanium layer of thickness 20, 50, and 80 μm is deposited in vacuum. This type of loading makes it possible to compare the behaviors of the homogeneous and double-layer conductors in identical conditions. It is shown that using the double-layer structure of the conductor with an external layer of thickness 20–80 μm with a lower conductivity, which is obtained by vacuum arc deposition, higher values of magnetic induction (as compared to homogeneous conductor) can be attained on its surface prior to plasma formation and spread.     

The use of explosion in fabrication of new materials

Abstract

The energy of high explosives have been widely used for some time in improving characteristics of the existing materials as well as for creating new materials having good prospects for different technological applications. The two last decades witnessed especially remarkable results in this field. In this paper we shall give a concise review of explosive metal hardening and welding processes, explosive compaction of metalxnon-metal materials as well as of the equipment used in industrial applications of these and some other processes of explosive treatment of materials.     

Initial stage of the explosion of ammonium nitrate and its powder mixtures

There is an obvious contradiction between the statistics of the devastating explosions that take place with the participation of ammonium nitrate and explosive properties of this material determined in standard tests. Pure ammonium nitrate does not burn under normal conditions and has a very low sensitivity to conventional mechanical and thermal stimuli. So far, ammonium nitrate has been detonated only by using high explosives. Causes of accidental explosions involving large masses of ammonium nitrate are likely to be found in a nonconventional behavior of ammonium nitrate. These changes may arise due to different chemical or physical factors, such as those associated with the presence of active additives, crushing of particles, etc., and lead to acceleration of the process at the initial stage of explosion. This work is devoted studying the convective burning and the initial stage of deflagration-to-detonation transition in dry and wet mixtures of ammonium nitrate with various, largely combustible additives. Experiments were conducted on loose-packed charges in a constant-volume bomb and by using the method of the critical bed height with recording pressure-time diagrams by a piezoelectric sensor. Ammonium nitrate of two different types was used: granular and powdered. The fuel additives were charcoal and aluminum powder, whereas the additives inhibiting the combustion of ammonium nitrate were water and monosodium salt of phosphoric acid. In addition, finely dispersed mixture of four components (ammonium nitrate, aluminum, powdered sugar, and TNT in a proportion of 76: 8: 12: 4) was used. The experiments in the constant-volume bomb were supplemented by numerical simulations, which made it possible to obtain a better understanding of the convective burning of the test mixtures and to evaluate the possibility of using a constant-volume bomb to collect quantitative information on the intensity of the combustion of the mixture at the initial stage of the explosion.     

The large-scale vortex structures in plasma-like media and the electric explosion of conductors

Formation of large-scale hydrodynamic convective patterns in plasma-like current-carrying media is considered. This process is shown to be described by the same equations, as Benard rolls, except that a temperature field must be replaced by a magnetic field. A simple low-mode model of spatial pattern formation for a case of cylindrical liquid-metal conductor with current is proposed and investigated. Nonlinear interaction of perturbations of the magnetic field and the velocity field results in an increase of effective conductor resistance even when transport coefficients are constant. In our opinion, it is this instability, that is of first importance at the initial stages of the electric explosion of conductors. In particular, it leads to conductor stratification and electric current interruption. (c) 1996 American Institute of Physics.     

Combustion and explosion of hydrogen-air mixtures under conditions imitating elements of gas-laden rooms

The time evolution of the processes of combustion and explosion with regard to safety problems in handling reactive gas mixtures was studied. The explosion safety for reaction volumes and gas-laden rooms can be assessed only if data on the possible consequences of the emergencies under conditions close to real ones or modeling them are available. The propagation of nonplanar explosion waves with a short positive phase in volumes with variable cross section is an essentially unsteady process. Until recently, the regularities of the evolution of the characteristics of such waves during their propagation in a reactive mixture with heat release virtually have not been studied. At the same time, these processes determine the character of combustion, and, therefore, the possibility of their formalization provides the opportunity to treat the entire variety of combustion regimes. Only a knowledge of general laws of the interaction of unsteady gasdynamic processes and gaskinetic processes in a reactive medium makes it possible to control combustion regimes purposefully and effectively. The present work is devoted to studying the propagation of combustion in cavities with a geometry imitating elements of reaction volumes and rooms filled with a hydrogen-air mixture. Results for a pyramid-shaped cavity capable of cumulating flows and waves are considered and compared to those obtained using a conical cavity [1–5].     

Phase composition and defect substructure of nickel alloyed with boron and copper by electric explosion of conductors

Using methods of electron microscopy, we have discovered that combined electroexplosive alloying of nickel with boron and copper gives rise to a multilayer structure. An outer amorphous crystalline layer incorporating 2–3 nm nickel-and copper-boride, oxide, and boride-oxide crystallites is formed on the alloyed surface. The intermediate (subsurface) layer 1–2 μm thick is made up of NiB ₁₂ and Ni ₄ B ₃ crystallites 120–130 nm in size, with boron-and copper-oxide particles observed along the grain boundaries. The underlying thick layer exhibits a cellular Ni-Cu-B melt crystallization structure grading initially into a high-rate dendritic crystallization structure and then into a granular structure. The electroexplosive alloying process is found to bring into existence a high scalar dislocation-density substructure in nickel crystallites both in the alloyed zone and in the adjacent heat-affected zone. __________ Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 3–7, March 2007.     

Low losses left-handed materials with optimized electric and?magnetic resonance

We propose that the losses in left-handed materials (LHMs) can be significantly affected by changing the coupling relationship between electric and magnetic resonance. A double bowknot shaped structure (DBS) is used to construct the LHMs. And the magnetic resonance of the DBS, which resonated in the case of lower and higher frequencies than the electric resonant dip, is studied in simulation and experiment by tailoring the structural parameters. The case of magnetic resonance located at low electric resonance frequencies band is confirmed to have relatively low losses. Using full wave simulation of prism shaped structure composed of DBS unit cells, we prove the negative refraction behavior in such a frame. This study can serve as a guide for designing other similar metal–dielectric–metal (MDM) in low losses at terahertz or higher frequencies.     

EDXRF determination of impurities in potassium dihydrogenphosphate single crystals and raw materials

A fast and simple preconcentration procedure for recovering various cation impurities from potassium dihydrogenphosphate (KDP) single crystals and raw materials, followed by energy‐dispersive X‐ray fluorescence analysis (EDXRF), is described. The technique is based on the adsorption of metal 8‐hydroxyquinoline complexes from aqueous solutions of KDP on activated carbon, separation of the concentrate on a Nuclepore filter and subsequent determination by EDXRF. To fix activated carbon powder on a filter surface, an amount of 1‐hexadecanol is added to the KDP solution during the preconcentration procedure. The optimum conditions for the best recovery of the impurities were established. It was shown that a preconcentration factor of 100 can be achieved and the detection limit for a number of elements was down to 0.01 µg g^?1. The relative standard deviations were 6–17% for element concentrations of 0.2 µg g^?1. The method was successfully applied to the determination of Fe, Co, Cu, Ni, Zn, Mn, Ti and Bi in KDP single crystals and raw materials. Copyright © 2005 John Wiley & Sons, Ltd.     

Effects of Soret diffusion on the laminar flame speed and Markstein length of syngas/air mixtures

The effects of Soret diffusion on premixed syngas/air flames at normal and elevated temperatures and pressures are investigated numerically including detailed chemistry and transport. The emphasis is placed on assessing and interpreting the influence of Soret diffusion on the unstretched and stretched laminar flame speed and Markstein length of syngas/air mixtures. The laminar flame speed and Markstein length are obtained by simulating the unstretched planar flame and positively-stretched spherical flame, respectively. The results indicate that at atmospheric pressure the laminar flame speed of syngas/air is mainly reduced by Soret diffusion of H radical while the influence of H₂ Soret diffusion is negligible. This is due to the facts that the main reaction zone and the Soret diffusion for H radical (H₂) are strongly (weakly) coupled, and that Soret diffusion reduces the H concentration in the reaction zone. Because of the enhancement in the Soret diffusion flux of H radical, the influence of Soret diffusion on the laminar burning flux increases with the initial temperature and pressure. Unlike the results at atmospheric pressure, at elevated pressures the laminar flame speed is shown to be affected by the Soret diffusion of H₂ as well as H radical. For stretched spherical flame, it is shown that the Soret diffusion of both H and H₂ should be included so that the stretched flame speed can be accurately predicted. Similar to the laminar flame speed, the Markstein length is also reduced by Soret diffusion. However, the reduction is found to be mainly caused by Soret diffusion of H₂ rather than that of H radical. Moreover, the influence of Soret diffusion on the Markstein length is demonstrated to decrease with the initial temperature and pressure.     

Effect of electric field on diffusion in disordered materials

The effect of electric field on diffusion of charge carriers in disordered materials is studied by Monte Carlo computer simulations and analytical calculations. It is shown how an electric field enhances the diffusion coefficient in the hopping transport mode. The enhancement essentially depends on the temperature and on the energy scale of the disorder potential. It is shown that in one‐dimensional hopping the diffusion coefficient depends linearly on the electric field, while for hopping in three dimensions the dependence is quadratic.     

Initiation of explosion-induced transformations in energy-saturated materials with nanoadmixtures by a high-voltage electric discharge

We have reported on the results of an experimental investigation of the effect of inert admixtures on the threshold characteristics of the breakdown (initiation) voltage in energy-saturated materials. A physicomathematical model that describes the experimental results has been proposed.     

Features of the hydrodynamic pressure field of an electric explosion in an equilibrium gas-liquid medium

The hydrodynamic features of an electric explosion in a bubble gas-liquid mixture are studied in the equilibrium approximation of the medium for the case of fine gas bubbles when the initial size of the latter ranges from units to tens of micrometers, as is observed when actual liquids contain natural gas. In mathematically modeling the electric-explosion processes, the characteristics of the hydrodynamic field were calculated, taking into account the finite size of the plasma piston for which the quasi-wave equation with the nonlinear barotropic equation of state of the mixture was numerically integrated, using an explicit finite-difference scheme in an ellipsoidal coordinate system. It is established that the presence of gaseous inclusions manifests itself when the gas concentration is ɛ ₀≳10⁻⁴, whereas appreciable nonlinear effects appear when ɛ ₀≳5×10⁻³. Zh. Tekh. Fiz. 68, 7–12 (July 1998)     

脉冲大电流放电引爆含能材料产生冲击波的储层改造

介绍了复合电热化学法产生冲击波的机理和冲击波改善储层物性的机制;给出了脉冲大电流引爆含能材料弹丸的结构和典型的放电参数,开展了冲击波致裂储层的实验研究;检测了样品在冲击作用下的动态应变及影响储层解吸附特性的关键参数（包括孔隙度、渗透率、抗拉、抗压强度等）,并在实验前后进行了测量和对比。研究表明,电热化学法产生的冲击波可在圆柱形砂岩样品上产生幅值为1000~1500的应变量,使砂岩出现了宏观裂缝;样品平均孔隙度由15.24%增至15.62%,平均渗透率由1.749 0910-3 m2增至2.467 0810-3 m2;抗压、抗拉和抗剪强度均下降了约30%。