A Low‐Sensitivity Composition Based on FOX‐7

1,1‐Diamino‐2,2‐dinitroethene (DADNE, FOX‐7) is considered to be an explosive combining comparatively high performance and low sensitivity. In the present study, FOX‐7 has been evaluated as a possible replacement of RDX in TNT‐based melt‐cast compositions. A composition containing FOX‐7, TNT, Al and wax, and a method of preparing it were proposed. Its sensitivity to impact, friction, shock wave, jet impact, fast heating, and its thermal stability were tested. Some detonation parameters like the detonation pressure, velocity and heat were measured. Moreover, the Gurney velocity, the so‐called effective exponent of the expansion isentrope and the JWL equation of state of the detonation products were determined from the results of a cylinder test. The detonation characteristics were compared with that obtained for cast TNT.     

Method for the Determination of the Critical Diameter of High Velocity Detonation by conical geometry

A critical diameter exists for both high velocity (HVD) and low velocity detonation (LVD). No relationship exists between these two diameters, however they are both dependent upon the temperature, confinement, contaminants, type of detonation and, most importantly, geometry. In cylindrical geometry, the critical diameter is determined by go/no go tests which are relatively expensive and time consuming. In this respect, there is a need for a method by which the critical diameter can be determined quickly and reliably. A relatively simple procedure which can also be performed in the field is proposed in this article where the critical diameter is determined in principle by a single test through the application of conical geometry. However, on account of “overdrive”, the values always fall below those obtained by cylindrical geometry. Metal plating is proposed as a method of indication. The results are then compared simultaneously by optical and electrical measurements. The temperature dependence of the critical diameter of the HVD of pure nitromethane was also demonstrated by conical geometry and was compared to the values of cylindrical geometry. The method was originally proposed as a joint US/German effort between Dr. Mallory of NSWC, China Lake, and Dr. Leiber of BICT. Since Dr. Mallory has recently passed away, the question is therefore open as to whether or not this test can be approved internationally.     

Shock Initiation of the CL‐20‐Based Explosive C‐1 Measured with Embedded Electromagnetic Particle Velocity Gauges

Hexanitrohexaazaisowurtzitane (CL‐20) is a high‐energy material with high shock sensitivity. The evolution of shock into the detonation of CL‐20 deserves academic attention and research. An embedded electromagnetic particle velocity gauge was used to study the shock initiation of detonation in a pressed solid explosive formulation, C‐1, containing 94 wt‐% epsilon phase CL‐20 and 6 wt‐% fluororubber (FPM). In conventional experiments, the magnetic field was generated using a pair of electromagnets with a complex structure and operation. A new device was designed to solve complex problems. This device comprised NdFeB magnets, pole shoes and magnetic yokes; using this technique, a uniform magnetic field could be created. A series of shock initiation experiments on high‐explosive C‐1 was performed, and the explosive samples were initiated at different intensity input shocks by an explosive driven flyer plate. In situ magnetic particle velocity gauges were utilized to detail the growth from an input shock to detonation, and the attenuation of particle velocity in unreacted C‐1 was also obtained in low‐intensity shock initiation experiments. Hugoniot data for C‐1 in the form of shock velocity D vs. particle velocity Up were obtained. A simulation model for shock initiation of C‐1 was established, and the particle velocity data from several experiments were used to determine the parameters required for the unreacted equation of state and ignition and growth reactive flow model for C‐1. These coefficients were then applied in the calculation of the initial shock pressure−distance to detonation relationship (Pop‐plot) for the explosive. Based on the results of experiments and simulations, the shock sensitivity characteristic of C‐1 was described.     

Stabilization of unstable detonation waves in mixtures of nitromethane with inert diluents

Mass velocity profiles of detonation waves in mixtures of nitromethane with acetone and methanol with added diethylenetriamine sensitizer were measured using a VISAR laser interferometer. It was found that even small, about 1%, concentrations of acetone and methanol, inert diluents, led to instability of the one-dimensional detonation front in nitromethane. The results of the experiment show that the use of the sensitizer is an effective method of flow stabilization and if the concentration of the inert diluent does not exceed 10%, the detonation front becomes stable with the addition of 1% diethylenetriamine. At a higher diluent concentration, the sensitizer does not suppress the instability but decreases the oscillation amplitude by several times. The addition of diethylenetriamine to the mixture has been found to increase the detonation velocity.     

Low and High Order Detonation in Tetryl

The detonation behaviour of tetryl has been investigated by analysing published charge diameter effect data for two mesh sizes of powders, using slightly divergent flow theory. Evidence found within the published data for the existence of high and low order detonation velocities regimes has been substantiated. The form of the global heat release function during low order detonation was found to be of the hot spot/grain burning type, and during high order detonation, of the thermal explosion type. Particle size effects are discussed both for low and high order detonation. The observed stability of low order detonation at the smaller charge diameters is explained in the model used, which predicts a ‘forbidden zone’ in shock velocity/inverse charge diameter space. The kinetics are discussed in terms of the pressure dependent functional form used in the CPeX detonation model, and models of hot spot formation in powder explosives.     

Application of Crystal Lattice Disintegration Criteria to Compute Minimum Shock induced reactive conditions in solid explosives and inert materials

A threshold particle velocity criteria derived by E.R. Fitzgerald for the beginning of crystal lattice breakup and disintegration has been applied to shocked explosives and an inert material. In shocked explosives, reactions leading to detonation occur above a certain “threshold” magnitude. The computed crystal lattice breakup shock pressures compare rather well with observed experimental “threshold” shock pressures for six high explosives. The six explosives are: Comp-B3, Comp-B, TNT, PBX-9404, Tetryl, and H-6. In addition, the crystal lattice breakup criteria provides an explanation for the observed lowering of the detonation “threshold” shock pressure as the explosives are made more porous or less dense. Finally, the shock pressures, at which output from thermocouples embedded in shocked materials (PBX-9404 and Plexiglass) increases dramatically, compare favorably with predictions based on crystal lattice disintegration criteria. Consequently, it is tentatively concluded that crystal lattice breakup, or self-sustained phonon fission as Fitzgerald calls it, is responsible for the initiation of detonation in shocked explosives and enhanced thermocouple output in shocked materials. It is also postulated that the lattice breakup phenomena is also responsible for phase changes, increased chemical reactivity, and anomalous electrical activity which are observed in certain inert materials under relatively low level shock loading.     

Effect of Scale and Confinement on Gap Tests for Liquid Explosives

The factors influencing initiation of detonation in gap tests for liquid explosives are investigated experimentally. A calibrated donor charge (nitromethane) and PMMA attenuator disk arrangement are used to transmit shocks of known strength (2–10 GPa) into a test explosive of nitromethane sensitized with 5% diethylenetriamine. The test explosive is contained in capsules of different wall materials (PVC, Teflon, aluminum), and the dimensions of the charges vary from 25 mm to 100 mm in diameter. For the small‐scale charges, the presence of the confining wall of the test capsule is seen to have a pronounced effect on the detonation initiation. Certain wall materials (PVC, Teflon) exhibit a multi‐valued critical gap thickness, meaning that a weaker shock may result in initiation while a stronger shock does not. The effect of the wall materials could not be correlated with their acoustic or shock impedance, and the only way to eliminate these effects was to make the diameter of the test charge larger than the donor charge. When the size of the donor charge was increased, the critical pressure required for initiation decreased. These results could be correlated to “ideal” shock initiation experiments that use flyer plates as shock sources assuming that lateral rarefactions quench detonation initiation if they reach the central axis of the charge before the onset of detonation is complete.     

Theoretical Investigation of Several 1,2,3,4‐Tetrazine‐Based High‐Energy Compounds

The enthalpies of formation of six 1,2,3,4‐tetrazine‐based compounds were calculated according to the Density Functional Theory BOP/TNP method and by using homodesmotic reaction designs. Their detonation performances, including detonation velocity and pressure, were predicted in terms of the Stine equations. The 1,2,3,4‐Tetrazine‐based compounds labeled A, B, C, D, and F are powerful high‐energy compounds. The detonation performances of A and B, including detonation velocity, and detonation pressure, are superior to that of the current high‐energy explosive CL‐20. The detonation velocity, detonation pressure, and oxygen balance of 1,2,3,4‐tetrazine related oxo derivatives can be improved by partial oxidation of the nitrogen atoms in the tetrazine ring, but further oxidation causes reduction of the enthalpies and specific impulses of the oxo derivatives. Calculation of the molecular resonance energies indicated that E [C₆N₁₂] and F have more negative values, i.e, the ring strain energies of their configurations are high, whereas the resonance energies of C and D are low, only compound B has a very positive resonance energy. Considering energy and stability, B is a promising compound for practical use with both high energy and low sensitivity.     

Low-Sensitivity Explosive Compounds for Low Vulnerability Warheads

Looking for explosives for Low Vulnerability Ammunitions leads to an interest in explosive molecules less sensitive than the usual nitramines (RDX, HMX). If TATB is quite convenient in terms of sensitivity, its performance is too low. The researches described here are related to synthesis and use of NTO (nitrotriazolone), another insensitive molecule. The synthesis by nitration of TO (triazolone) is easy and the two steps from available starting materials have been optimized. A comparison of desensitivation of PBX either by TATB or by NTO have been made. The sensitivity levels were found equivalent while the detonation velocity of the NTO based PBX was slightly higher. Unfortunately in this case, the failure diameter would be larger. The last part relates to an extensive characterization in terms of performance and vulnerability to fast cook off, slow cook off, bullet impact, shock sensitivity and sympathetic detonation of a NTO and HMX based PBX. This PBX, B 2214, was one of the first examples of explosive composition showing no sympathetic detonation, even in 248 mm large diameter.     

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.     

用电磁粒子速度计实验研究一种TATB基钝感炸药的冲击响应

针对一种新的TATB基钝感炸药(Tx),应用组合式电磁粒子速度计(EMV)测试技术,测量了炸药直接加载、增加有机玻璃隔板以及炸药驱动飞片3种加载状态下炸药内部的粒子速度历程和冲击波轨迹。根据测试结果,分析了不同加载压力下炸药的冲击响应过程。结果表明,炸药直接加载时,加载压力最高,Tx钝感炸药很快达到爆轰状态,到爆轰距离约为1.5mm;在增加有机玻璃隔板、加载压力为14.2GPa时,与直接加载时炸药粒子速度一致,Tx钝感炸药的到爆轰距离明显增加,约为5mm;在炸药驱动飞片、加载压力为9.5GPa时,Tx钝感炸药的粒子速度逐渐降低,存在一定钝化现象,到爆轰距离达到20mm以上。     

Laboratory‐Scale Method for Estimating Explosive Performance from Laser‐Induced Shock Waves

A new laboratory‐scale method for predicting explosive performance (e.g., detonation velocity and pressure) based on milligram quantities of material is demonstrated. This technique is based on schlieren imaging of the shock wave generated in air by the formation of a laser‐induced plasma on the surface of an energetic material residue. The shock wave from each laser ablation event is tracked for more than 100 μs using a high‐speed camera. A suite of conventional energetic materials including DNAN, TNT, HNS, TATB, NTO, PETN, RDX, HMX, and CL‐20 was used to develop calibration curves relating the characteristic shock velocity for each energetic material to several detonation parameters. A strong linear correlation between the laser‐induced shock velocity and the measured performance from full‐scale detonation testing has been observed. The Laser‐induced Air Shock from Energetic Materials (LASEM) method was validated using nitrocellulose, FOX‐7, nano‐RDX, three military formulations, and three novel high‐nitrogen explosives currently under development. This method is a potential screening tool for the development of new energetic materials and formulations prior to larger‐scale detonative testing. The main advantages are the small quantity of material required (a few milligrams or less per laser shot), the ease with which hundreds of measurements per day can be obtained, and the ability to estimate explosive performance without detonating the material (reducing cost and safety requirements).     

Measurement and calculation of the ideal detonation velocity for liquid nitrocompounds

Results of experimental measurements are presented for the dependence of the detonation velocity on the charge diameter for homogeneous nitromethane and propylene glycol dinitrate and for the ideal detonation velocities for allyl nitrate, diethlyene glycol dinitrate, methylene glycol dinitrate, and ethyl nitrate. Literature data on measurement of the dependence of the detonation velocity on the charge diameter for liquid TNT, nitroglycerin, glycol dinitrate, and methyl nitrate are collected. It is shown that measured values of the ideal detonation velocity are in good agreement with calculated values obtained by the SD method, which uses the equation of state of materials at a high pressure (see B. N. Kondrikov and A. I. Sumin, Fiz. Goreniya Vzryva, No. 1, 1987). A correlation between the ratio of the critical detonation velocity to the ideal velocity and the heat of explosion is obtained, which makes it possible to estimate the limiting value of the latter at which homogeneous liquid nitrocompounds lose detonatability. Translated fromFizika Goreniya i Vzryva, Vol. 34, No. 5, pp. 111–117, September–October 1998.     

Shock Compression and Initiation of LX-10

LX-10 is a high energy density solid explosive consisting of 94.5% octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and 5.5% Viton A Binder pressed to 1.865 g/cm³ (98.4% of theoretical maximum density). In this paper the shock compression and initiation of chemical reaction in LX-10 by sustained shock pressures of 0.4 to 3 GPa are studied experimentally using embedded pressure and particle velocity gauges. The resulting pressure and particle velocity histories are evaluated theoretically using the ignition and growth reactive flow computer model of shock initiation and detonation. Manganin resistance and polyvinylidene fluoride (PVF₂) ferroelectric pressure gauges are both employed in the low pressure (0.4 – 0.7 GPa) shock compression experiments. Multiple manganin pressure and multiple electromagnetic foil particle velocity gauges measure the growth of reaction at various positions in LX-10 shocked to 1 – 3 GPa. The reactive flow modeling results imply that less than one percent of the LX-10 shocked to 0.4 – 0.7 GPa reacts in fifteen microseconds. For the higher pressure experiments, the ignition and growth model accurately calculates the pressure and/or particle velocity buildup in LX-10 as the reaction grows toward detonation. The LX-10 calculations are compared to those for the well-calibrated explosive PBX-9404, which contains 94% HMX and a reactive binder. Since it has the inert binder Viton A and better mechanical properties than PBX-9404, LX-10 is demonstrated to be significantly less reactive than PBX-9404 at these shock pressures. Therefore LX-10 is safer than PBX-9404 in many hazard and vulnerability scenarios to which solid explosives may be subjected.     

On the validity of the thermal explosion model in shock wave initiated nitromethane

By means of Perot Fabry Velocimetry (PFV) we recorded material velocities generated by an intense shock wave (P > 70 kbar) in pure nitromethane. Our experiments show that nitromethane does not behave according to the Campbell-Travis model for detonation in liquid explosives. We do not find any evidence for a so-called superdetonation, which would start behind and overtake the pressure shock wave. Our recordings of material velocities show a behavior of the liquid explosive very similar to that of solid polycrystalline explosives and are compatible with the heterogeneous decomposition scheme.     

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.     

Estimated Detonation Velocities for TKX‐50, MAD‐X1, BDNAPM,BTNPM, TKX‐55, and DAAF using the Laser–induced Air Shock from Energetic Materials Technique

Since new energetic materials are initially produced in very small quantities for both safety and cost reasons, laboratory‐scale methods for characterizing their performance are essential for determining the most promising candidates for scale‐up. Laser‐induced air shock from energetic materials (LASEM) is a promising new method for estimating the detonation velocity of novel explosives using milligram amounts of material, while simultaneously investigating their high temperature chemical reactions. LASEM has been applied to 6 new explosives for the first time: TKX‐50, MAD−X1, BDNAPM, BTNPM, TKX‐55, and DAAF. Emission spectroscopy of the laser excited materials revealed the formation of the high pressure bands of C₂ during the ensuing exothermic reactions. The low thermal sensitivity of the materials also led to unusual laser‐material interactions, visualized with high‐speed video. The estimated detonation velocities for the 6 explosives were compared to predicted values from EXPLO5 and CHEETAH. The LASEM results suggest that TKX‐55, BDNAPM, and BTNPM have higher detonation velocities than predicted by the thermochemical codes, while the estimated detonation velocities for MAD−X1 and TKX‐50 are slightly lower than those predicted.     

Detonation characteristics of diluted liquid explosives: Mixtures of nitromethane with methanol

Detonation in mixtures of nitromethane with methanol as an inert (nonexplosive) diluent is studied. Ignition experiments with mixtures in steel tubes of various diameters provided information on the effect of the degree of dilution on detonability. Mass velocity profiles with a chemical spike characteristic of detonation waves were recorded at the unsteady detonation front in all mixtures studied. This made it possible to distinguish the Chapman-Jouguet state and obtain a fairly complete set of detonation parameters. The dependence of the pressure in the detonation products on the methanol concentration is determined, which is required, in particular, to find the true (absolute) limit of detonation propagation for the concentration of diluted liquid explosives using the method proposed and validated by A. N. Dremin. Some results were found to be inconsistent with one-dimensional detonation theory.     

Influence of Ammonium Nitrate Prills' Properties on Detonation Velocity of ANFO

Prilled/granulated ammonium nitrate is commonly used as a fertilizer and a basic ingredient of industrial explosives, especially of ANFO. One of the most important factors that affect the explosive properties of ANFO is the porosity of the prills/granules. This paper describes an attempt to manufacture ammonium nitrate prills of determined porosity in order to investigate its influence on the ANFO detonation velocity. A method of manufacturing porous ammonium nitrate prills with a high‐level of oil absorption (up to 20% by volume) was developed. The relations between porosity and granulometric distribution of ammonium nitrate prills versus the detonation velocity of ANFO were examined. It has been proved that the detonation velocity of ANFO increases significantly with higher porosity and smaller size of ammonium nitrate prills/granules. The influence of ANFO oxygen balance (researched by changing the content of fuel oil in the mixture) on detonation velocity has been determined for two kinds of ammonium nitrate prills–one with a low and another one with a high level of porosity.     

Shock Velocity Measurement in Water by Sulfur Probes

Sulfur-coated pin oscillographic technique (SPOT) has been developed as a new technique for measurement of shock velocity in water. Unlike other techniques, generally employing piezoelectric transducer or high speed photography, the application of this technique is not restricted to the measurement of shock wave pressures over a limited range. To illustrate the application and accuracy of the technique the detonation pressures of a few typical explosives have been measured with this technique and compared with those determined elsewhere by using other techniques. The new technique has yielded measurement of shock velocity in water within an accuracy of 2%.