Effects of N-oxide on the thermal stability of energetic materials: A case study of 2,6-Diamino-3,5-dinitropyrazine-1-oxide

Finding new insensitive high explosives has been the focus of the energetic materials community in recent decades. To accelerate the discovery process, it is necessary to elucidate the relationship between molecular structure and the performance of explosives. In this regard, the effects of N-oxide groups, commonly introduced to increase the energy density of explosives, on the thermal stability of explosives were investigated by comparing the thermal behaviors of a typical energetic N-oxide, ANPZO, and its analogue ANPZ. The presence of N-oxide facilitated the thermal decomposition of ANPZO thoroughly and suppressed its sublimation to a certain extent. Compared to ANPZ, the introduction of N-oxide increased the thermal enthalpy, reduced the solid residues, and shortened the acceleration period of thermal decomposition of ANPZO. Additionally, the sublimation rate and vapor pressure of ANPZO were lower than those of ANPZ. The enthalpy of sublimation for ANPZO was 175.1 kJ mol⁻¹, compared to 135.2 kJ mol⁻¹ for ANPZ. The effects of N-oxide on the thermal decomposition and sublimation are attributed to its contribution to the augmentation of oxygen sources and intermolecular interactions, respectively. This study provides further insight into the relationship between the N-oxide group and the performance of explosives, which could be beneficial for the design and application of new explosives.     

PBX炸药细观结构冲击点火的二维数值模拟

为了研究冲击加载下非均质炸药的点火机理,对PBX炸药细观结构在冲击加载下的响应过程进行了二维数值模拟.首先对炸药颗粒的压制过程进行数值模拟,获得PBX炸药的细观结构模型.然后对炸药冲击点火进行数值模拟计算,考虑了热力耦合作用和炸药自热反应,分析了炸药颗粒尺寸、密度和黏结剂对炸药冲击点火的影响.结果表明,冲击作用下PBX...     

Altering Reactivity of Aluminum with Selective Inclusion of Polytetrafluoroethylene through Mechanical Activation

Micrometer‐sized aluminum is widely used in energetics; however, performance of propellants, explosives, and pyrotechnics could be significantly improved if its ignition barriers could be disrupted. We report morphological, thermal, and chemical characterization of fuel rich aluminum‐polytetrafluoroethylene (70–30 wt‐%) reactive particles formed by high and low energy milling. Average particle sizes range from 15–78 μm; however, specific surface areas range from approx. 2–7 m² g⁻¹ due to milling induced voids and cleaved surfaces. Scanning electron microscopy and energy dispersive spectroscopy reveal uniform distribution of PTFE, providing nanoscale mixing within particles. The combustion enthalpy was found to be 20.2 kJ g⁻¹, though a slight decrease (0.8 kJ g⁻¹) results from extended high energy milling due to α‐AlF₃ formation. For high energy mechanically activated particles, differential scanning calorimetry in argon shows a strong, exothermic pre‐ignition reaction that onsets near 440 °C and a second, more dominant exotherm that onsets around 510 °C. Scans in O₂‐Ar indicate that, unlike physical mixtures, more complete reaction occurs at higher heating rates and the reaction onset is drastically reduced (approx. 440 °C). Simple flame tests reveal that these altered Al‐polytetrafluoroethylene particles light readily unlike micrometer‐sized aluminum. Safety testing also shows these particles have high electrostatic discharge (89.9–108 mJ), impact (>213 cm), and friction (>360 N) ignition thresholds. These particles may be useful for reactive liners, thermobaric explosives, and pyrolants. In particular, the altered reactivity, large particle size and relatively low specific surface area of these fuel rich particles make them an interesting replacement for aluminum in solid propellants.     

Sensitiveness of Porous Silicon‐Based Nano‐Energetic Films

Nanoporous silicon (pSi) films on a silicon wafer were loaded with sodium perchlorate and perfluoropolyether (PFPE) oxidizing agents. Sensitiveness to impact, friction and electrostatic discharge (ESD) of the resulting energetic thin films were investigated. It was observed that pSi loaded with perchlorate was sensitive at the lowest limit of detection for the available equipment (<4.9 J impact energy, <5 N friction force, and <45 mJ ESD spark energy). When loaded with PFPE the material was very sensitive to impact (<4.9 J), moderately sensitive to ESD (between 45 and 100 mJ) and insensitive to friction (>360 N). pSi loaded with either perchlorate or PFPE displayed behavior during sensitiveness testing similar to other primary explosive materials.     

用C80量热仪研究重铵油炸药的热分解特性

借助C80微量量热仪研究了多孔粒状铵油炸药、3种常用的重铵油炸药（乳化炸药/多孔粒状铵油炸药质量百分比分别为25/75、50/50、75/25）、乳化炸药的热分解特性,以升温速率0.2 K·min^-1时的C80热流速曲线数据为基础,求解了5种炸药试样热分解反应的反应热（ΔH）、表观活化能（E_a）、指前因子（lnA）等热力学和动力学参数。结果表明：乳化炸药的存在抑制了多孔粒状铵油炸药的热分解反应,使其开始发生热分解反应的温度被明显提高。重铵油炸药的表观活化能和放热反应开始温度均高于多孔粒状铵油炸药和乳化炸药,由此得出重铵油炸药的热稳定性高于多孔粒状铵油炸药和乳化炸药的热稳定性。     

Thermal Initiation of Non‐Electric Detonators

Cookoff – the concept of heating explosives to ignition – is a useful tool for determining issues that may be related to safely using and storing explosives, and as such, cookoff experiments have been performed on many different materials. All explosive systems require a means of initiation, which is usually a detonator: a device that often contains a sensitive, primary explosive and a more powerful, secondary explosive. Even if the cookoff behaviors of all the individual explosives in an explosive system are known, the behavior of the combined system may be quite different. In this experiment, the cookoff behavior of non‐electric detonators is investigated. It was determined that there was no distinguishable difference between initiating detonators properly or heating them at a rate greater than 10 °C min⁻¹. Heating detonators at rates less than 10 °C min⁻¹ diminished their output.     

CFD Cook‐Off Simulation and Thermal Decomposition of Confined High Energetic Material

The handling, storage and safety before deployment of explosives are major key issues that confront the ammunition industry. Precautions have to be taken not to cause premature detonations and fatal accidents by studying their thermal behaviour. Research has been conducted to investigate the thermal stability of some secondary explosives such as RDX, HMX and TNT and their response to thermal stimuli. For the fact that real experiment which involves large amount of explosives can be potentially dangerous, cook‐off numerical simulation and experiment has been regarded as the best method to analyse such thermal behaviour of explosives. Prominent among these researches involve experiment and numerical analysis such as ODTX, SITI, and DDT experiments. In this work, numerical CFD simulation will be executed for the thermal behaviour of TNT including cook‐off and thermal decomposition. The heating rates were varied for both slow and fast cook‐off cases. In view of these thermal decomposition reactions which mainly consist of kinetic parameters were factored in the numerical simulation as well as the critical thermodynamic physical properties. To effectively handle the reactions, UDF was employed. Attention was paid on the melting time to ignition of explosive, the location likely for ignition occurrence, as well as temperature distribution in the course of the heating process. CFD simulation results showed that the location of ignition was around the supplementary charge.     

Characterization of ADN and ADN‐Based Propellants

Ammonium dinitramide (ADN), NH₄N(NO₂)₂ is being considered as one of the potential new energetic oxidizers for composite propellants. In this study, ADN crystals, prills and two ADN‐based propellants having different relative amounts of ingredients were characterized. The concentration of the crystals and the prills samples was determined using ion chromatography. The thermal behavior of the crystals, prills and propellants was studied using DSC, simultaneous TG‐DTA‐FTIR‐MS, ARC (accelerating rate calorimeter), HFC (heat flux calorimeter) and INC (isothermal nanocalorimeter). Decomposition of ADN was observed from all of the samples at temperatures above the melting point of ADN (~ 92 °C). Formation of N₂O, NO₂, H₂O, CO₂, CO, N₂ and NO was detected during the ADN decomposition. The thermal stability of the ADN samples at temperatures below the melting point of ADN was studied. Early solid decomposition of ADN, which generates N₂O and H₂O, was observed at 60 °C. Electrostatic discharge (ESD) and impact sensitivity of the ADN samples were determined. The crystals and prills are sensitive to impact, while the two propellants are relatively less ESD and impact sensitive.     

Aminotetryls: Synthesis,spectral characterization,thermal decomposition and explosive properties

This paper describes the synthesis and spectral investigations of two amino derivatives of N-methyl-N-(2,4,6-trinitrophenyl)nitramine (tetryl). Also discussed are the results from thermal decomposition studies on the three explosives, viz. tetryl, 3-aminotetryl (3 AT) and 3,5-diaminotetryl (3,5 DAT) and preliminary work on the explosive properties of the last two compounds. The aminotetryls have been prepared by the amination of the corresponding chlorotetryls. The yield was 87% for 3 AT, but was only 33% for 3,5 DAT, probably due to steric crowding around the benzene nucleus. The mass spectra show interesting differences in the electron impact fragmentation patterns of the three tetryls with the M⁺ ion relative intensities following the order 3,5 DAT > 3 AT > tetryl, which could be due to (a) resonance stabilization and (b) hydrogen bonding effects. Evidence for the latter is also found in the infrared spectra of these compounds. Arrhenius kinetic parameters derived from thermal decomposition studies of the three compounds are presented and show that 3,5 DAT is thermally less stable than 3 AT. Explosive sensitiveness tests indicate that the diamino compound is the most sensitive, the trend being 3,5 DAT > 3 AT > tetryl. This is contrary to the generally found desensitizing influence of NH₂ groups on the thermal stability and explosive sensitiveness of trinitroaromatic energetic molecules. Mechanisms to account for the observed thermal decomposition behaviour and explosive sensitiveness patterns are discussed.     

Polypyrrole material for the electrostatic discharge sensitivity mitigation of Al/SnO2 energetic composites

Nanothermites are composite energetic materials made of fuel and oxidizer nanoparticles characterized by impressive exothermic reactions (highly flame temperatures and impressive heat combustion releases). However, nanothermites suffer from their high electrostatic discharge (ESD) sensitivity that may be at the origin of accidental ignitions during handling. The present study deals with the use of doped-polypyrrole conducting polymer in aluminum/tin (IV) oxide energetic formulation (Al/SnO₂). X-ray diffraction, Fourier transforms infrared spectroscopy, scanning electron microscopy, conductivity measurements, sensitivities and combustion tests were implemented to characterize the polypyrrole-doped Al/SnO₂ energetic composite. The results revealed a significant gradual ESD desensitization of the nanothermite (<0.14 mJ to 246.40 mJ) as a function of the doped-polypyrrole amount (0 to 15 wt%). The reactive properties of the polypyrrole-enriched Al/SnO₂ nanothermite were verified and an acceptable reactive behavior was claimed. The successful adding of doped-polypyrrole conducting polymer within energetic nanocomposites is reported for the first time.     

低强度冲击下炸药点火的数值模拟

为了研究炸药在低强度冲击下的反应特性,根据标准的Steven试验建立了数值计算模型,采用热力耦合模型和Arrhenius方程描述炸药的热反应,对不同速度弹头撞击炸药过程进行了数值模拟计算,获得了炸药点火的弹头阈值速度,分析了弹头形状对炸药反应的影响。计算结果表明,在弹头阈值速度下,炸药点火存在一定的延迟时间,随着弹头速度的增大,延迟时间缩短;弹头形状会影响炸药受力过程,使炸药点火特性发生变化。     

A DSC Analysis of Inverse Salt‐pair Explosive Composition

Alkali nitrates are used as an ingredient in low explosive compositions and pyrotechnics. It has been suggested that alkali nitrates can form inverse salt‐pair explosives with the addition of ammonium chloride. Therefore, the thermal behavior of low explosive compositions containing potassium nitrate mixed with ammonium chloride has been studied using Differential Scanning Calorimetry (DSC). Results provide information about the ion exchange reaction between these two chemical substances and the temperature region at which the formation of a cloud of salt particles of potassium chloride takes place. Furthermore, the addition of ammonium chloride quenches the flame of deflagrating compositions and causes the mixture to undergo explosive decomposition at relatively low temperatures.     

Reformulation of solid propellants and high explosives: An environmentally benign means of demilitarizing explosive ordnance

Polymer Bound Explosives (PBXs) and Class 1.1 Military Propellants have been reformulated for use in the mining industry. There is a minimal waste stream. The explosives are sensitive to initiation by a #8 cap. Impact sensitivities have routinely passed 5 kg meter stimuli, initiation by 50,000 V AC and the BAM friction protocols at 1000 rpm under a 11 kg load for 10 seconds. The explosives were packed into sticks, slurried or used as pourable mixes. VoDs of 2.4 to 6.2 km/s were realized with τ = 0.9 — 1.35 t/m³. The explosives have powers comparable to a range of dynamites. The Beaver Code based upon Lotus 1.2.3 —g^TM was developed to predict explosive properties.     

Composite Propellant Based on a New Nitrate Ester

Composite propellants based on the solid nitrate ester 2,3‐hydroxymethyl‐2,3‐dinitro‐1,4‐butanediol tetranitrate (SMX) were theoretically and experimentally examined and compared to formulations based on ammonium perchlorate (AP). Thermochemical equilibrium calculations show that aluminized SMX‐based formulations can achieve theoretical sea level specific impulse values upwards of 260 s. Both ignition sensitivity (tested via drop weight impact, electrostatic discharge, and BAM friction) and physical properties (hardness and thermal properties) are comparable to those of the AP‐based formulations. However, the SMX‐based formulation could be detonated using a high explosive donor charge in contact with the propellant. Differential scanning calorimetry of the SMX‐based propellant indicated an exotherm onset of 140 °C, which corresponds to the known decomposition temperature of SMX. The propellant has a high burning rate of 1.57 cm s⁻¹ at 6.89 MPa, with a pressure exponent of 0.85. This high pressure sensitivity might be addressed using various energetic and/or stabilizing additives. With good performance and high density, SMX‐based composite propellants may offer a promising perchlorate‐free alternative to existing AP‐based formulations.     

Combustion of Nanoaluminum and Water Propellants: Effect of Equivalence Ratio and Safety/Aging Characterization

The deflagration and combustion efficiency of 80 nm aluminum/ice (ALICE) mixtures with equivalence ratios of ϕ=1.0, 0.75, and 0.67 were experimentally investigated. We find that pressure exponent and burning rate vary little between these three mixtures, with the exponent varying only from 0.42 to 0.50 and burning rate at 6.9 MPa varying from 2.05 to 2.10 cm s⁻¹. However, reducing the equivalence ratio from 1.0 to 0.67 surprisingly increases combustion efficiency from 70 % to 95 % with unburned aluminum agglomerates visible in electron microscopy photographs of 70 % combustion efficiency (ϕ=1.0) products. Our findings suggest that nanoaluminum/water combustion is diffusionally limited for all conditions considered. Aging tests on the propellant show that storage at −30 °C essentially stops the Al/H₂O reaction such that little nanoaluminum degradation occurs after 200 days. Electrostatic discharge (ESD), shock initiation, and impact sensitivity tests indicate that the propellant is insensitive to ignition by these stimuli. Specifically, while neat nanoaluminum powders are highly ESD sensitive (ignition threshold 0.3–14 mJ), nAl/H₂O mixtures are insensitive to ESD and have ignition thresholds in excess of 400 mJ. Likewise, nAl/H₂O mixtures are insensitive to impact ignition, having an ignition threshold in excess of 2.2 m. Propellants containing 80 nm or larger average particle size aluminum were also found to be insensitive to shock initiation.     

Highly Thermal Stable TATB‐based Aluminized Explosives Realizing Optimized Balance between Thermal Stability and Detonation Performance

In this work, a series of TATB‐based aluminized explosives were formulated from 1, 3, 5‐triamino‐2, 4, 6‐trinitrobenzene (TATB), aluminum powders and polymeric binders. The thermal stability, heat of detonation, detonation velocity and pressure of the TATB based aluminized (TATB/Al) explosives were systematically investigated by cook‐off, constant temperature calorimeter, electrometric method and manganin piezo resistance gauge, respectively. The selected PBX‐3 (70 wt% TATB/25 wt% Al/5 wt% fluorine resin) achieved optimized balance between thermal stability and detonation performance, with the thermal runaway temperature around 583 K. The thermal ignition of TATB‐based aluminized explosive occurred at the edge of the cylinder according to the experimental and numerical simulations. Moreover, the critical thermal runaway temperature for PBX‐3 was calculated based on the Semenov's thermal explosion theory and the thermal decomposition kinetic parameters of the explosive, which was consistent with the experimental value.     

Preparation and Properties Study of Core‐Shell CL‐20/TATB Composites

The insensitive high explosive 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB) was selected for coating and desensitization of hexanitrohexaazaisowurtzitane (CL‐20), another high explosive, after surface modification. About 2 wt‐% polymer binder was adopted in the preparation process to further maintain the coating strength and fill the voids among energetic particles. The structure, sensitivity, polymorph properties, and thermal behavior of CL‐20/TATB by coating and physical mixing were studied. Scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS) results indicate that submicrometer‐sized TATB was compactly coated onto the CL‐20 surface with coverage close to 100 %. The core‐shell structure of CL‐20/TATB was confirmed by observation of hollow TATB shell from the CL‐20 core dissolved sample. X‐ray diffraction (XRD) analysis revealed that the polymorph of CL‐20 maintained ε form during the whole preparing process. Thermal properties were studied by thermogravimetry (TG) and differential scanning calorimeter (DSC), showing effects of TATB coating on the polymorph thermal stability and exothermic decomposition of CL‐20. Both the impact and friction sensitivities were markedly reduced due to the cushioning and lubricating effects of TATB shell. The preparation of explosive composites with core‐shell structure provides an efficient route for the desensitization of high explosives, such as CL‐20 in this study.     

一维热爆炸试验传热的数值模拟

针对加热过程所涉及的主要传热学问题,分别建立空气夹层复合传热模型和炸药受热分解放热数值模型;计算分析了473K下油浴和空气浴加热时系统辐射率、空气对流换热系数对RDX、HMX、TATB 3种炸药热点火延滞时间的影响。结果表明,473K油浴加热和空气浴加热时RDX分别在151.7s和3 372.6s时发生热点火,表明相同温度和炸药,油浴加热时热点火延滞时间远小于空气浴加热;空气浴加热时,同一种炸药在相同温度下,随系统辐射率的降低,热点火延滞时间增加;RDX、HMX和TATB炸药辐射率由0.9降至0.1时,热点火延滞时间分别增加了180.1%、168.9%和169.3%;相同温度、相同系统辐射率条件下,对流换热系数减小,热点火延滞时间增加。     

Laser Ignition of Nano‐Composite Energetic Loose Powders

Laser ignition experiments were conducted to better understand parameters that influence ignition of energetic materials. A Nd:YAG laser (10 ms, 1.5 J, 3 mm spot diameter) was used to heat the top surface of an energetic powder composed of nanometric aluminum (Al) combined stoichiometrically with an oxidizer (copper oxide (CuO), iodine pentoxide (I₂O₅), polytetrafluoroethylene (C₂F₄), molybdenum trioxide (MoO₃) or iron oxide (Fe₂O₃)). Ignition delay time was calculated as the difference between first light of the laser’s flash lamp and the energetic material. Results show that laser energy required for ignition is dependent on pre‐ignition reactions, phase change/decomposition temperatures, confinement, and laser absorbance.     

Characterisation of the Major Synthetic Products of the Reactions Between Butanone and Hydrogen Peroxide

The reactions between butanone and hydrogen peroxide, both catalysed and un‐catalysed, were investigated and spectral and sensitiveness data reported. The major product of the un‐catalysed reaction, 2‐hydroxy,2‐hydroperoxybutane, displayed a Figure of Insensitiveness (F of I) of 10, Temperature of Ignition (T of I) of 132 °C, and initiated when 128 N of frictional force or an electrostatic discharge (ESD) of 4.5 J was applied. Differential scanning calorimetric analyses revealed an onset of decomposition at 128 °C, peak maximum of 140 °C, and decomposition energy of 203 J g⁻¹. The major product of the cooled (5 °C) acid catalysed reaction between butanone and hydrogen peroxide, 2,2′‐dihydroperoxy‐2,2′‐dibutyl peroxide, displayed a F of I of<10, T of I of 110 °C and initiated upon application of 5 N of friction or a 0.45 J ESD. Calorimetry showed a melt at 38.3 °C, an onset of exothermic decomposition at 127 °C and the evolution of 1292 J g⁻¹. The major product of the raised temperature (20 °C) acid catalysed synthesis, 1,4,7‐trimethyl‐1,4,7‐triethyl‐1,4,7‐cyclononatriperoxane, displayed F of I of<10 and initiated upon application of 5 N of friction or a 0.45 J ESD. Calorimetry revealed an onset to melting at 28.9 °C, an onset to thermal decomposition at 128 °C, and decomposition energy of 1438 J g⁻¹.