Initiation Of Explosives Research Articles

1-AminoTriazole Transition-Metal Complexes as Laser-Ignitable and Lead-Free Primary Explosives.

This unique complex study describes two isomeric aminotriazoles as auspicious nitrogen-rich ligands for energetic coordination compounds (ECCs) to replace the commonly used highly poisonous and environmentally harmful lead-based primary explosives. The triazoles were obtained by easily scalable and convenient synthetic routes starting solely from commercially available starting materials. 1-Amino-1,2,3-triazole (1, 1-ATRI) and, for the first time, 1-amino-1,2,4-triazole (2, 1A-1,2,4-TRI) were employed as ligands to form highly energetic transition-metal(II) complexes. The desired characteristics could be altered successively by using various nonpoisonous metal(II) centers (Cu2+ , Mn2+ , Fe2+ , and Zn2+ ) and anions (Cl- , NO3 - , ClO3 - , ClO4 - , picrate, styphnate, 2,4,6-trinitro-3-hydroxyphenolate, and 2,4,6-trinitro-3,5-dihydroxyphenolate). The 14 synthesized coordination compounds were characterized comprehensively by XRD, IR and UV/Vis spectroscopy, elemental analysis, and differential thermal and thermogravimetric analyses. Ball-drop impact, electrostatic discharge (ESD), and mechanical (impact and friction) sensitivities were determined according to BAM standard methods. In addition to laser ignition experiments, selected ECCs were evaluated in classical secondary explosive initiation tests (detonators filled with pentaerythritol tetranitrate (nitropenta)), which revealed their enormous potential and proved them to be very attractive for future applications in explosives.

Design and Validation of Blast Non-propagation Wall for Multi-Compartmented Explosive Storage Structure of Capacity 5T NEC per Compartment

Conventional magazines for hazard division 1.1 are constructed using bricks and reinforced cement concrete (RCC) for which storage inside quantity distance (SIQD) is 2.4 W1/3 m, where W is Net Explosive Content in kg. New composite called laced reinforced concrete (LRC) has been developed recently, for which SIQD has been reduced up to 0.5 W1/3 m. Due to substantial reduction in separation distances, the requirement of land area has been reduced significantly. Although SIQD has been reduced drastically due to development of new composite, the other quantity distances like process inside quantity distance (PIQD) and outside quantity distance (OQD) decreased marginally. To reduce these quantity distances, the solution is multi-compartmented structures based on Unit Risk Principle. The application of unit risk principle enables the separation of explosives into compartments in such a manner that initiation of explosives in one compartment does not result in initiation of the explosives in adjacent compartments. This is achieved by special design of explosive storage buildings incorporating blast non-propagation walls between adjacent compartments storing explosives. Quantity distances are reduced for such magazines, as maximum credible limit corresponds to the quantity of explosive in one compartment. Present paper describes design and full scale testing of blast non-propagation wall between two compartments of a multi-compartmented explosive storage structure with storage capacity of 5 T Net Explosive Content (NEC) of HD 1.1 per compartment. The blast non-propagation wall comprising of sand filling and air gap between LRC walls has been designed for desired attenuation of blast parameters as well as for arresting high velocity fragments/debris. The design has been validated by fully instrumented design validation field trial. The conduct of the trial as well as the results are discussed in this paper.

Experimental studies on explosive limits and minimum ignition energy of syngas: A comparative review

Syngas, as one cleaner and efficient approach to coal utilization, has been widely regarded as one promising alternative fuel. Owing to the existence of hydrogen molecule, syngas has a great potential to explosion which would be favoured by thermo-power devices but be worried by safety issues on the processes of production, storage, and delivery. Explosive limits and minimum ignition energy are two essential but crucial aspects for the initiation of explosion, and thus a well understanding on those issues should be a prerequisite for massive utilizations. This paper has presented a comprehensive review on the recent progress in the experimental studies on the explosive limits and minimum ignition energy for syngas. Some essential conclusions and some interesting observations have been remarked, and the potential of further studies have been prospected.

ABLATION AND DRIVE OF TYPICAL MULTI-LAYER FLYERS BY HIGH POWER LASER BEAM

Laser driving technology is an important technology in high energy physics, shock wave physics and explosive initiation application. In this paper, velocities and impact stresses of four types of laser-driven flyers (Al, Al/Al2O3/Al, CuO/Al2O3/Al, (CuO/Al)/Al2O3/Al) prepared via magnetron sputtering were obtained by photonic Doppler velocimetry (PDV) and a self-made polyvinylidene fluoride (PVDF) stress sensor at ns-class pulse width.The results showed that velocities and integrity of flyers were influenced by their diameters. Compared with Al single-layer flyer, other multi-layer flyers with Al2O3 insulation layer owned lower velocity but better integrity and initiation properties.CuO/Al as the ablation layer enhanced the velocities and shock initiation properties of multi-layer flyers. Velocity of a flyer improved with the increasing laser energy while shock initiation property did not perform in the same way. These results provide some references for the design of multi-layer flyers applied to laserdriven initiation technology.

The response characteristics of warhead fragment impact on shielded H6 explosive

For studying response characteristics resulting from fragmentation warhead fragment impact on shielded H6 explosive. H6 explosive has been shielded with Q235 steel, what was impacted for cuboid tungsten fragments at the velocity range of 2000 m/s~2200 m/s launching from 25 mm ballistic gun, with different quality and length-thick ratio of square, The process of impact response was observed by high-speed photography. The maximum diameter and duration of the fireball as well as destruction of shielded H6 explosive were recorded, then corresponding features of shielded H6 explosive were analyzed accordingly. Furthermore, the mechanism of H6 explosive responses was analyzed based on the theory of explosive impact initiation. Results show that it mainly includes combustion, deflagration and detonation for response features of targets, and it has highest probability for deflagration. Adiabatic shear effect was regarded as the functional mechanism, which could produce different response characteristics. Deflagration reactions could be sparked in which of the situations the quality of fragments was no less than 10 g. what's more, the most violent deflagration reactions could be sparked under the certain condition that the length-thick ratio of fragment was about 1.6.

Reactive Structural Materials: Preparation and Characterization

Reactive structural materials, which can serve both as structural elements as well as a source of chemical energy released upon initiation have emerged as an important class of metal‐based composites for use in various energetic systems. Such materials rely on a variety of exothermic reactions, from oxidation to formation of metal‐metalloid and intermetallic phases. The rates of these reactions are as important as the energy that may be released, in order for them to occur at the time scales compatible with the requirements of applications. Therefore, chemical composition, scale at which reactive components are mixed, and the structure and morphology of materials are important and can be controlled by the method of preparation and compaction of the composite materials. Methods of preparation of the composite structures are briefly reviewed as well as methods of characterization of their mechanical and energetic properties. In addition to common thermo‐analytical and static mechanical property measurements, dynamic tests of mechanical properties as well as ignition and combustion experiments are necessary to understand the fragmentation, initiation, and heat release expected for these materials when they are stimulated by an impact, shock, or rapid heating. Reaction mechanisms are studied presently for the thin layers and small samples of reactive materials initiated in carefully designed experiments. In other experiments, impact and explosive initiation are characterized for larger material compacts in the conditions imitating practical scenarios. Examples of results describing thermal, impact, and explosive initiation of some of the reactive materials are presented.

Shock initiation of explosives: High temperature hot spots explained

We investigated the shock initiation of energetic materials with a tabletop apparatus that uses km s−1 laser-driven flyer plates to initiate tiny explosive charges and obtains complete temperature histories with a high dynamic range. By comparing various microstructured formulations, including a pentaerythritol tetranitrate (PETN) based plastic explosive (PBX) denoted XTX-8003, we determined that micron-scale pores were needed to create high hot spot temperatures. In charges where micropores (i.e., micron-sized pores) were present, a hot spot temperature of 6000 K was observed; when the micropores were pre-compressed to nm scale, however, the hot spot temperature dropped to ∼4000 K. By comparing XTX-8003 with an analog that replaced PETN by nonvolatile silica, we showed that the high temperatures require gas in the pores, that the high temperatures were created by adiabatic gas compression, and that the temperatures observed can be controlled by the choice of ambient gases. The hot spots persist in shock-compressed PBXs even in vacuum because the initially empty pores became filled with gas created in-situ by shock-induced chemical decomposition.

Numerical simulation and experimental study of explosive projectile devices

A study of explosive-throwing device (ETD) was undertaken to simulate the hypervelocity impact of space debris fragments (SDF) and meteoroids with spacecrafts. The principle of operation of an ETD is based on the cumulative effect in combination with the cut-off head of the cumulative jet, which enables one to simulate a compact particle, such as a meteoroid or a fragment of space debris. Different design schemes of ETD with different composition explosive charge initiation schemes with notably low speeds of the jet cut-off are explored, and a method to control the particle velocity is proposed. Numerical simulation of device modes and basic technical characteristics of experimental testing are investigated.

Determination of the Firing Pin Critical Velocity and the Critical Power in the Percussive Initiation of Primer Caps

This work involved testing of the probability of initiating a KWM-3 type of primer cap as a function of the firing pin velocity upon impact. The tested firing pin was accelerated to the required velocity by a falling mass. The measurements under this work were made with a measurement system and methodologies developed at Air Force Institute of Technology (AFIT) in Warsaw (Poland). The percussive pulse velocity and power was altered by modifying the percussive mass to keep the initiating pulse energy constant at two levels: Ewe = 272 mJ and 343 mJ. The firing pin velocity values estimated by experimental data to bring a 50% probability of percussive primer cap initiation were within the interval vi50% = 0.34÷0.51 m/s. It was found that the mean primer cap ignition delay rose from approx. 0.7 ms at a percussion velocity of 1.5 m/s to 6 ms at 0.17 m/s. The experimental data suggest the values of Ewe x vi50% = 0.136. A simplified model was proposed for the deformation of the primer cap base and compressed pyrotechnical mixture shape. The model served to determine the approximate time trend for the penetration of the primer cap by the firing pin, including velocity, power and emitted energy, by assuming a complete energy transfer from the percussive mass to the primer cap. The mean initiating pulse power calculated from the model at the vi50% interval was Pavg = 120÷180 W, whereas the maximum initiating pulse power was Pmax = 170÷250 W. The calculated time values for firing pin penetration were very close to the aforementioned primer cap ignition delays at the respective velocity and percussive mass values. This indirectly indicates nearly complete energy transmission from the percussive masses to the primer caps. A location was identified within the compressed pyrotechnical mixture shape volume which could form the hot spot for initiation of the explosive reaction. Based on the calculation results using the simplified model, and assuming that the energy and diffusive heat flux output to and from the explosive reaction initiation hot spot were equivalent, the expression of Ewe x vi50% derived from the result was approx. 0.18. This means that the two critical parameters of primer cap initiation: (i) velocity, which can be identified with vi50% (and the respective power) and (ii) Ewe50%, i.e. the energy threshold below which the probability of primer cap initiation is less than 0.5, are interrelated. Aside from the initiation mechanism proposed and applied to calculate the firing pin critical velocity, this work discusses several other initiation mechanisms, all of which were ruled out during the testing process.

Insight into electrostatic initiation of nitramine explosives.

The electrostatic safety of explosives is of great importance. However, the mechanism for the transfer of energy from an electrostatic spark to the reactive center of an explosive material is not well understood. Thus, in this work, we attempted to clarify the mechanism associated with the static-electricity-initiated detonation of explosives using a model of the interaction that incorporated relevant parameters. Nitramine explosives were considered as examples to study the relationship between electrostatic spark energy and 32 relevant parameters. The four parameters that were most closely correlated with the electrostatic spark energy were the standard deviation of the negative electrostatic potential, the minimum surface electrostatic potential, the minimum ionization energy, and the detonation pressure. A model for the dependence of the electrostatic spark energy on these four parameters was derived using the theoretical method known as genetic function approximation. The electrostatic spark energy values predicted using this model were in good agreement with the corresponding experimental values. The results of this work should lead to a deeper understanding of the electrostatic initiation mechanism of nitramines, and help to inspire the design of new explosives.

Characteristics of the initiation of chain and thermal explosions of energetic materials by pulsed laser radiation

A comparative experimental and theoretical study of the initiation of silver azide (SA) single crystals and pressed pentaerythritol tetranitrate (PETN)–metal nanoparticles by a neodymium laser pulse is performed. The main differences in the explosive decomposition of the samples are associated with the absence of the induction period and the presence of subthreshold effects in the initiation of PETN-based composites. By contrast, the initiation of SA single crystals always features an induction period, but no subthreshold effects. It is shown that the observed differences in the explosive decomposition are due to the fact that SA single crystals decompose by the chain explosion mechanism, whereas pressed PETN–metal nanoparticles samples, by the thermal explosion mechanism in the micro-hotspot mode. The kinetic parameters of the initiation of the decomposition reaction calculated within the framework of the existing model are consistent with the available experimental data. An experimental criterion for distinguishing between the chain and thermal (in micro-hotspot) mechanisms of the initiation of an explosion under the action of a laser radiation pulse is formulated, according to which the absence of the induction period and a pronounced manifestation of subthreshold effects are indicative of a thermal explosion, whereas the presence of the induction period and the absence of subthreshold effects are characteristic of a chain explosion.

Laser initiation of PETN-based composites with additives of ultrafine aluminium particles

This paper describes the study on the dependence of the critical energy density of the explosive decomposition of PETN on the mass concentration of the additives of ultrafine Al particles (100–120 nm) in the range of 0.025–1% under the influence of the first and second harmonics of a neodymium laser (12 ns, 1064 and 532 nm). It is shown that the critical energy of the explosion initiation by the first and second harmonics of the laser radiation reaches a minimum value at the same absorption rates, but different concentrations of additives. The photoacoustic method is used to show that, as the laser energy radiation is absorbed, the pressure amplitude in the heated layer reaches a maximum value when the concentration of additives corresponds to the minimum value of the critical energy density.

Energetic material response to ultrafast indirect laser heating.

The initial evolution of thermal energy transfer into a solid explosive is studied using an indirect femtosecond laser heating technique on a picosecond timescale in order to elucidate the role of temperature in the shock-induced initiation of explosives. The indirect laser heating method is presented; time-resolved visible transient absorption (TA) spectroscopy was used to monitor the energetic material response following heat transfer from the laser-heated gold (Au) layer to the sample. Reported here are visible TA data in the spectral region from 500 to 750nm for indirect laser-heated thin films of cyclotrimethylene trinitramine (RDX), oxidized polyethylene (OPE), and RDX with 1%, 2.5%, 5%, or 10% OPE prior to decomposition. TA was observed for RDX and RDX with OPE; however, no TA was observed for pure OPE. Compared to pure RDX, the TA intensity of RDX with OPE decreases as the OPE content increases and the time required to observe the TA signal from RDX increases. Our results suggest that the thermal energy produced by a femtosecond laser pulse with an energy of 15 mJ cm-2 is sufficient to induce changes in the electronic structure of RDX, resulting in promotion of the RDX molecules into an excited state. We also determined that the heat transfer rate in RDX depends on its homogeneity and degree of purity.

Shock initiation of explosives: Temperature spikes and growth spurts

When energetic materials are subjected to high-velocity impacts, the first steps in the shock-to-detonation transition are the creation, ignition, and growth of hot spots. We used 1–3.2 km s−1 laser-launched flyer plates to impact powdered octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine, a powerful explosive, and monitored hundreds of emission bursts with an apparatus that determined temperature and emissivity at all times. The time-dependent volume fraction of hot spots was determined by measuring the time-dependent emissivity. After the shock, most hot spots extinguished, but the survivors smoldered for hundreds of nanoseconds until their temperatures spiked, causing a hot spot growth spurt. Depending on the impact duration, the growth spurts could be as fast as 300 ns and as slow as 13 μs.

A physically-based Mie–Grüneisen equation of state to determine hot spot temperature distributions

A physically-based form of the Mie–Grüneisen equation of state (EOS) is derived for calculating 1d planar shock temperatures, as well as hot spot temperature distributions from heterogeneous impact simulations. This form utilises a multi-term Einstein oscillator model for specific heat, and is completely algebraic in terms of temperature, volume, an integrating factor, and the cold curve energy. Moreover, any empirical relation for the reference pressure and energy may be substituted into the equations via the use of a generalised reference function. The complete EOS is then applied to calculations of the Hugoniot temperature and simulation of hydrodynamic pore collapse using data for the secondary explosive, hexanitrostilbene (HNS). From these results, it is shown that the choice of EOS is even more significant for determining hot spot temperature distributions than planar shock states. The complete EOS is also compared to an alternative derivation assuming that specific heat is a function of temperature alone, i.e. cv(T). Temperature discrepancies on the order of 100–600 K were observed corresponding to the shock pressures required to initiate HNS (near 10 GPa). Overall, the results of this work will improve confidence in temperature predictions. By adopting this EOS, future work may be able to assign physical meaning to other thermally sensitive constitutive model parameters necessary to predict the shock initiation and detonation of heterogeneous explosives.

Laser initiation of PETN–iron nanoparticle composites

The dependences of the probability of explosion initiation in pentaerythritol tetranitrate samples with different contents of iron nanoparticles on the fluence of the first- (λ = 1064 nm) and second-harmonic (λ = 532 nm) pulses of a neodymium laser are measured. The laser initiation threshold for PETN–iron nanoparticle composites nonmonotonically depends on the mass fraction of nanoparticles. The optimal values of the mass fraction of iron nanoparticles at which the sensitivity to laser irradiation is maximal (0.4 wt % for the first harmonic and 0.15 wt % for the second) are determined. It is demonstrated that the amplitude of the optoacoustic signal under non-explosion conditions reaches its maximum for composites with the optimal values of the mass fraction of nanoparticles.

A mesoscopic reaction rate model for shock initiation of multi-component PBX explosives

The primary goal of this research is to develop a three-term mesoscopic reaction rate model that consists of a hot-spot ignition, a low-pressure slow burning and a high-pressure fast reaction terms for shock initiation of multi-component Plastic Bonded Explosives (PBX). Thereinto, based on the DZK hot-spot model for a single-component PBX explosive, the hot-spot ignition term as well as its reaction rate is obtained through a “mixing rule” of the explosive components; new expressions for both the low-pressure slow burning term and the high-pressure fast reaction term are also obtained by establishing the relationships between the reaction rate of the multi-component PBX explosive and that of its explosive components, based on the low-pressure slow burning term and the high-pressure fast reaction term of a mesoscopic reaction rate model. Furthermore, for verification, the new reaction rate model is incorporated into the DYNA2D code to simulate numerically the shock initiation process of the PBXC03 and the PBXC10 multi-component PBX explosives, and the numerical results of the pressure histories at different Lagrange locations in explosive are found to be in good agreements with previous experimental data.

Hot spot formation and chemical reaction initiation in shocked HMX crystals with nanovoids: a large-scale reactive molecular dynamics study.

We report million-atom reactive molecular dynamic simulations of shock initiation of β-cyclotetramethylene tetranitramine (β-HMX) single crystals containing nanometer-scale spherical voids. Shock induced void collapse and subsequent hot spot formation as well as chemical reaction initiation are observed which depend on the void size and impact strength. For an impact velocity of 1 km s(-1) and a void radius of 4 nm, the void collapse process includes three stages; the dominant mechanism is the convergence of upstream molecules toward the centerline and the downstream surface of the void forming flowing molecules. Hot spot formation also undergoes three stages, and the principal mechanism is kinetic energy transforming to thermal energy due to the collision of flowing molecules on the downstream surface. The high temperature of the hot spot initiates a local chemical reaction, and the breakage of the N-NO2 bond plays the key role in the initial reaction mechanism. The impact strength and void size have noticeable effects on the shock dynamical process, resulting in a variation of the predominant mechanisms leading to void collapse and hot spot formation. Larger voids or stronger shocks result in more intense hot spots and, thus, more violent chemical reactions, promoting more reaction channels and generating more reaction products in a shorter duration. The reaction products are mainly concentrated in the developed hot spot, indicating that the chemical reactivity of the hmx crystal is greatly enhanced by void collapse. The detailed information derived from this study can aid a thorough understanding of the role of void collapse in hot spot formation and the chemical reaction initiation of explosives.

Preshock Desensitization Phenomena during Initiation of Covered Heterogeneous Explosives by Shaped Charge Jets

The initiation of heterogeneous explosives by shaped charge jets is discussed. A reactive flow model, specially modified to account for the desensitization effects due to preshocking in heterogeneous explosives, is used to investigate the initiation of explosives by a shaped charge jet. Previously reported shaped charge jet initiation experimental setups are simulated using hydrodynamic software LS-DYNA with the desensitization model implemented as a user-defined equation of state. The simulation results indicate that the desensitization effects caused by the shocks preceding the jet play a significant role in determination of the run to detonation distance for covered explosives initiated by jets. The failure in initiation in the first explosive sample that is in contact with the steel plate and initiation of the second sample separated further by an air gap during penetration of the jet can be explained on the basis of desensitization phenomena. The simulation qualitatively reproduces various shock interaction phenomenon occurring in explosives during penetration by a shaped charge jet.

Energetic nanocomposites for detonation initiation in high explosives without primary explosives

The mixing of aluminum nanoparticles with a metal containing oxidizer (here, WO3 or Bi2(SO4)3) gives reactive materials called nanothermites. In this research, nanothermites were combined with high explosive nanoparticles (RDX) to prepare energetic nanocomposites. These smart nanomaterials have higher performances and are much less hazardous than primary explosives. Their flame propagation velocity can be tuned from 0.2 to 3.5 km/s, through their explosive content. They were used to initiate the detonation of a high explosive, the pentaerythritol tetranitrate. The pyrotechnic transduction of combustion into detonation was achieved with short length systems (<2 cm) and small amounts of energetic nanocomposites (∼100 mg) in semi-confined systems.