Critical detonation diameter of industrial explosive charges: Effect of the casing

The critical detonation diameter of industrial explosive charges is analyzed as a function of their state characteristics (composition, density, and structure) and the presence of a casing. The main reason for the increase in the critical diameter with increasing density of ammonium nitrate explosive charges is the reduction in the energy release rate in the chemical reaction zone of the detonation wave. The effect of the particle size of the components and the amount of the sensitizing component on the critical diameter of powdered and granular explosives fits into the concept of explosive combustion. An analytical formula for the critical detonation diameter of emulsion explosives is obtained which correctly describes experimental data. A possible mechanism of the effect of metal casings on the critical detonation diameter is considered for porous explosives whose detonation velocity is lower than the sound velocity in the casing.     

Detonation Velocity of Emulsion Explosives Containing Cenospheres

The detonation velocity of an emulsion explosive containing hollow alumosilicate microspheres (cenospheres) as the sensitizer is measured. The size of the microspheres is 50–250 μm. The relations between the detonation velocity and the charge density and diameter are compared for emulsion explosives containing cenospheres or glass microballoons as the sensitizer. It is shown that for a 55 mm diameter charge, the maximum detonation velocity of the composition with cenospheres of size 70–100 μm is 5.5–5.6 km/sec, as well as for 3M glass microballoons. The critical diameter for the emulsion explosive with cenosphere is 1.5–2 times larger than that for the emulsion explosive with glass microballoons and is 35–40 mm. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 5, pp. 119–127, September–October, 2005.     

Experimental study on the effect of titanium hydride content on the detonation performance of emulsion explosives

In order to improve the explosion characteristics of emulsion explosives, titanium hydride was added to emulsion explosives to produce a new type of hydrogen storage emulsion explosives. Charges with different contents of titanium hydride were evaluated through underwater explosion experiments and detonation velocity tests. The tests on underwater explosion and detonation velocity reveal that compared to pure emulsion explosives, the detonation parameters of emulsion explosives containing titanium hydride showed a trend of first increasing and then decreasing. When the mass ratio of titanium hydride in the emulsion explosive is 1 % to 3 %, all detonation parameters have been improved to a certain extent. When the mass ratio of titanium hydride in the emulsion explosive is 3 % to 10 %, only part of the detonation parameters (specific impulse, specific shock energy, specific total energy and volume energy density) has been improved. The maximum increase of specific impulse, specific shock energy, specific total energy and volume energy density of emulsion explosive containing titanium hydride is 7.06 %, 8.95 %, 3.97 % and 8.22 %, respectively. Based on the analysis, it is evident that though powdered TiH₂ participates in the detonation reaction process of the emulsion explosive, the majority of TiH₂′s energy is released during the secondary reaction occurring after the detonation wave front. Therefore, the detonation performance of emulsion explosives can be effectively improved by adding a certain mass ratio of titanium hydride.     

Density dependence of detonation velocity for some explosives

The nonmonotonic dependence of the detonation velocity of a cylindrical charge on density for explosives of the 2nd type is due to the effect of the finite charge diameter and is related to an increase in the width of the reaction zone with a reduction in the porosity of the explosive. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 4, pp. 116–124, July–August, 2006.     

Detonation velocity of an emulsion explosive sensitized with polymer microballoons

This paper presents the results of investigation of the detonation velocity of an emulsion explosive sensitized with Expancel polymer microballoons in a wide range of initial density of 0.14–1.33 g/cm³. It is shown that at a density of the emulsion explosive less than 0.4 g/cm³, detonation with an unstable front characteristic of liquid explosives is possible.     

Limiting conditions of stable propagation of detonation with a one-dimensional zone in liquid explosives

Summary The critical diameter of condensed explosives with a one-dimensional zone is notdirectly connected with its width. It is considerably greater and is determined by the conditions of ignition and recovery of the detonation front after collapse of the ignition lag in the detonation wave zone by the lateral rarefaction wave.Since collapse in the zone transfers the heat release kinetics from degenerate to normal conditions, when an induction period, strongly dependent on temperature, appears, one would expect to find in these explosives a steep dependence of critical diameter on initial temperature, which is indeed observed in NG [9].It should be noted that the comparison in [9] between impact sensitivity and critical diameter is unfounded, since the critical diameter is determined by the effective activation energy and the degree of shock heating behing the collapse line, which, in turn, depends on the power of the explosive. In shock initiation the heating of the explosive is given by the parameters of the active charge, so that the power of the explosive itself does not take part directly. Thus, the impact sensitivity is determined only by the effective value of the activation energy.Fizika Goreniya i Vzryva, Vol. 2, No. 4, pp. 75–84, 1966     

Critical detonation diameter of a cased low-velocity emulsion explosive

The effect of the casing on the critical detonation diameter of a fine low-velocity emulsion explosive was examined experimentally. The critical diameter of a metalcased cylindrical charge is seven times smaller than that of the charge in a thin-walled polyethylene casing.     

Effect of the Initial Density on the Structure of Detonation Waves in Heterogeneous Explosives

Reaction zones in steady detonation waves in RDX, HMX, TNEB, and ZOX with different initial densities are studied with the use of a VISAR interferometer. The critical initial density which causes the qualitative change in the reaction-zone structure is determined: below the critical density, a chemical spike is registered, whereas above this density, the chemical spike disappears and an increase in pressure is observed. It is shown that the critical density for a given dispersion of high explosives depends on the method of charge pressing and equals 1.73, 1.84, 1.56, and 1.71 g/cm³ for RDX, HMX, TNETB, and ZOX, respectively. It is concluded that the unusual structure of the detonation wave is caused by the reaction of the high explosive directly in the shock-wave front. Key words: high explosives (HE), HE density, structure of detonation waves.     

Effect of small additions of diethylenetriamine on the width of the reaction zone in detonation waves in nitromethane

This paper presents the results of an experimental determination of the width of the reaction zone in a detonation wave in nitromethane sensitized by diethylenetriamine. It was found that increasing the mass concentration of diethylenetriamine from 0 to 2.0% reduced the typical reaction time by a factor of less than two while the critical diameter decreased by an order of magnitude. This discrepancy is explained by the fact that the critical detonation diameter of neat nitromethane is determined not by the reaction time but by flow instability at the edge of the charge, manifested in the occurrence of a wave of reaction disruption. Increasing the initial rate of nitromethane decomposition by addition of diethylenetriamine leads to flow stabilization and thus to a change in the nature of the critical diameter.     

Detonation of Secondary Explosives in a Vacuum Suspension

The existence of self–sustaining detonation in an evacuated suspension of the particles of a secondary explosive is shown experimentally. The experiments with HMX were performed in a vertical shock tube of diameter 0.07 m and length 7 m in the range of volume–average particle concentrations 0.32—0.9 kg/m³. It is shown that the vacuum–detonation velocity does not almost depend on the volume–average concentration of particles and it is (1750±50) m/sec and that the pressure profile of a vacuum–detonation wave is smooth. The data on the electric conductivity of vacuum–detonation products and the length of the reaction zone are given.     

Detonation characteristics of emulsion explosives

The detonation properties of a water-emulsion explosive are studied. The shock adiabat is determined for a density of 1.38 g/cm³. The critical diameter and the detonation velocity are found as functions of the initial density of the charge and the shock heating temperature is calculated.D. I. Mendeleev Moscow Institute of Chemical Technology, Moscow, 125190. Translated from Fizika Goreniya i Vzyrva, Vol.30, No. 3, pp. 86–91, May–June, 1994.     

Investigation of the reaction zone in heterogeneous explosives substances using an electrical conductivity method

A technique for measuring the electrical conductivity profile behind a detonation wave front with a resolution of about 0.1 mm was used to analyze the reaction zone in heterogeneous explosives. TNT-RDX mixtures, RDX with additives of water, NaCl, and a saturated aqueous solution of NaCl, and pure RDX of low density were studied. It was shown that the particle size of the explosive can have a significant effect on the structure of the reaction zone. The most narrow conducting zone (0.22 mm) was observed in fine RDX of density 1.2 g/cm³. __________ Translated from Fizika Goreniya i Vzryva, Vol. 45, No. 2, pp. 109–115, March–April, 2008.     

Effect of initial air pressure on the detonation activity of an explosive aerosuspension

The effect of air pressure (0.01–0.3 MPa) on the detonatability of an aerosuspension of secondary explosive particles at a low mean volume density of the explosive (0.14–1.28 mg/cm³) is experimentally studied. The structure and basic parameters of detonation depending on the explosive density and initial gas pressure are determined, and the mechanism of low-velocity detonation propagation in explosive aerosuspensions is revealed. The lower concentration limits of detonation at different initial gas pressures are found.     

Structure of detonation waves in PETN

A VISAR technique was used to study the structure of the reaction zone in PETN for various initial densities and dispersion of samples. The flow in the pressed charges corresponds to the classical denotation model. In the case of bulk density, the peculiarities corresponding to an explosive combustion model are recorded. In the vicinity of the initial density of 1.7 g/cm³, a kink is found on the curve showing detonation velocity versus density, and the shock-wave initiation of PETN above and below the kink point is studied.     

Detonation Performance of TATP/AN‐Based Explosives

The detonation velocity and performance were determined for four mixtures of triacetone triperoxide (3,3,6,6,9,9‐hexamethyl‐1,2,4,5,7,8‐hexoxonane, TATP), ammonium nitrate (AN) and water (W) by cylinder expansion tests. The composition of these mixtures varied in the following ranges: 21–31% TATP, 37–54% AN and 19–32% W. The obtained results were compared with those of powdery 2,4,6‐trinitrotoluene (TNT), AN‐fuel oil explosive (ANFO) and emulsion explosive. It was found that the tested TATP/AN/W mixtures represent typical non‐ideal explosives with relatively low critical diameter and with high sensitivity to initiation despite the high content of water due to the presence of the primary explosive (TATP). The detonation velocity is comparable to that of powdery TNT (at similar density). However, the acceleration ability is significantly lower than that of powdery TNT.     

Properties of porous cast charges based on mixtures of ammonium nitrate and carbamide

The explosive and physicochemical properties of porous mixtures based on ammonium nitrate, carbamide, and aluminum powder are considered. A melting curve for the ammonium nitrate/carbamide system is plotted using differential scanning calorimetry. The critical detonation diameter is obtained for a charge density of 0.6–0.7 g/cm³. The dependence of the charge density on the degree of filling of the mold with the melt is determined. Detonation velocity is measured for various densities. An explanation of the difference between the experimental and calculated values is proposed.     

含废弃丁羟推进剂的凝胶炸药

为安全处理和再利用废弃固体推进剂,通过添加单基药将丁羟推进剂再利用制备了灌注式凝胶炸药.采用验证板试验及电离探针法研究了不同装药配比、推进剂颗粒尺寸及装药直径对炸药爆轰性能的影响.结果表明,丁羟推进剂难以发生爆轰,若添加适量单基药,能显著提高炸药的爆轰感度,并降低其临界直径;该凝胶炸药密度为1.6 g/cm3,直径为7...     

Shock Initiation of Sheet Explosive

The shock sensitivity of a typical sheet explosive RDX-WAX (90:10) has been experimentally determined with gap test arrangement by measuring free surface velocity in different thicknesses of the barrier and shock and particle velocity of non-reactive shock wave in the sheet explosive with Pin Oscillography Technique. It has been found that a shock wave, generated by a point-initiated cylindrical explosive in contact with an aluminium barrier of diameter nearly twice the diameter of the charge, attenuates exponentially and a 6.5 mm thick sheet explosive, of density 1.28 g/cm³ and velocity of detonation 6.43 mm/μs, detonates with 50% probability by a shock wave of 11 kbar pressure in the explosive.     

Detonation velocity of mechanically activated mixtures of ammonium perchlorate and aluminum

The detonation properties of mechanically activated mixtures of ammonium perchlorate and aluminum were studied. The deflagration-to-detonation transition for low-density charges was investigated. Dependences of the detonation velocity of pressed charges with different types of aluminum on the activation time, density, and diameter of the charges were obtained. For compositions with nanosized aluminum, it is was found that the detonation velocity depends nonmonotonically on the inverse charge diameter and remains almost unchanged in a certain range of charge diameters. It is shown that the joint use of mechanical activation and nanosized components of the composite explosive significantly increases the detonability, reduces the critical diameter, and shifts the maximum of the detonation velocity as a function of density to higher charge densities.     

Detonation of PETN single crystals initiated by an electron beam

Luminescence in the volume of PETN (tetranitropentaerytrite) single crystals exposed to an electron beam (duration 20 nsec) with an energy density of 15 J/cm², which exceeds the threshold of explosive decomposition, was investigated in real time. Exposure to the ionizing pulse causes radioluminescence and emission related to the critical electron emission from a dielectric which is transformed to a vacuum discharge. The emission zone propagates from the surface into the vacuum at a speed of 5000–6500 m/sec. The absorption of electron beam energy in the irradiated layer (0.25 mm) causes the formation and propagation of a shock wave enhanced by the chemical reaction in the crystal. When the shock wave is reflected from the target on the rear side of the sample, its amplitude increases. This leads to detonation accompanied by emission which propagates from the backside to the irradiated surface of the sample at a speed of 7500–8500 m/sec with the subsequent expansion of the explosive decomposition products into the vacuum.