Energetic Residues from the Detonation of IMX‐104 Insensitive Munitions

The development of insensitive munitions by NATO countries is an ongoing effort. Less‐sensitive ingredients in both explosives and propellants will ensure the protection of deployed troops against an unwanted reaction to an external stimulus on the munitions stockpile. In the US Army, current efforts are directed towards the development of melt cast insensitive explosive formulations. Various formulations, mainly based on DNAN and NTO, have been developed and are now being fielded. Our research goal is to measure the deposition rate of energetics compounds from various insensitive munitions detonation scenarios. Our hypothesis is that the relative insensitiveness of these formulations leads to slightly higher deposition rates than conventional explosive formulations. This paper describes detonation residues research on mortar rounds containing IMX‐104 explosive. Analyses indicate that high‐order detonation residues are slightly greater for this formulation than for conventional munitions. However, blow‐in‐place detonations (BIPs) resulted in much higher residues deposition, indicating that a larger donor charge is required for efficient detonation. The highly soluble compound NTO was particularly problematic, with BIP deposition approaching 95 % of the original load. Toxicological studies of NTO are not finalized, leaving considerable uncertainty regarding the feasibility of approving these rounds for distribution.     

Partial Reparametrization of the BKW Equation of State for DNAN‐Based Melt‐Cast Explosives

DNAN‐based melt‐cast explosives are a type of new, insensitive munitions (IM) explosives. Quickly determining munitions’ explosive properties is extremely important during the formulation design stage. The aim of this study was to partially reparameterize BKW‐EOS (only β and κ were reparameterized on the basis of the parameters (α , β , κ , and θ ) of classical BKW‐RDX set and BKW‐TNT set) to more accurately predict the properties of DNAN‐based melt‐cast explosives. A new set of parameters β and κ was obtained (β =0.19, κ =9.81) according to measured detonation velocity and detonation pressure for ideal DNAN‐based melt‐cast formulations (DNAN/RDX and DNAN/HMX). For non‐ideal DNAN‐based melt‐cast formulations (DNAN/RDX/Al and DNAN/HMX/Al), aluminum oxidation degree was first determined according to the measured detonation heat; then, another new set of parameters β and κ was obtained in the same way as the ideal formulations (β =0.24, κ =8.5). The predicted detonation properties with BKW reparametrization for DNAN‐based melt‐cast explosives agreed with the measured data.     

Solubility Determination of Raw Energetic Materials in Molten 2,4‐Dinitroanisole

2,4‐Dinitroanisole (DNAN) is an ingredient used in several insensitive munition formulations that have recently been qualified by the US Army. A phenomenon known as irreversible growth is found to occur during conditioning cycles of insensitive munitions (IM) that contain DNAN. A possible cause of the irreversible growth maybe the potential solubility of energetic components formulated with melted DNAN. This report documents methods development and procedures used to determine the solubility of energetic constituents in molten DNAN at 100 °C. High performance liquid chromatography and ion chromatography were used for quantitation. Solubilities (given as g energetic per 100 g DNAN) of RDX, HMX, NTO, NQ, and AP were found as 13.7, 3.02, 0.222, 0.448, and 0.088, respectively.     

Thermal Stability Studies Comparing IMX‐101 (Dinitroanisole/Nitroguanidine/NTO) to Analogous Formulations Containing Dinitrotoluene

The 2,4,6‐trinitrotoluene (TNT) replacement, IMX‐101, containing 43.5 % 2,4‐dinitroanisole (DNAN), 19.7 % 3‐nitro‐1,2,4‐triazol‐5‐one (NTO) and 36.8 % nitro‐guanidine (NQ), has been certified for use as an insensitive munition. IMX‐101 has passed standardized performance, stability, and aging tests but in some categories was not necessarily an improvement over TNT or RDX. This study compared the thermal stability of DNAN and another low‐melting nitroarene, 2,4‐dinitrotoulene (DNT). When examined individually, DNAN was more stable; but formulated in IMX‐101 with NTO and NQ, the opposite was true. In two part mixtures, NQ had a similar acceleratory effect on the decomposition of both nitroarenes, while NTO had a greater impact on DNAN than on NTO. Ammonia, a reported decomposition product of both NQ and NTO, also accelerated the decomposition of both DNAN and DNT, with a larger impact on DNAN. The formation of dinitroaniline, potentially due to the interaction between the nitroarenes and ammonia, was detected by LC/MS as a decomposition product when either nitroarene was combined with NTO and/or NQ, indicating that this molecule may play a significant role in the decomposition mechanism. While not advocating the use of DNT in insensitive munitions formulations, this study addresses the importance of chemical compatibility as a criterion for selecting replacement components in formulations.     

Preparation and Characterization of Hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine/Ammonium Perchlorate Intermolecular Explosives

Hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine/ammonium perchlorate/glycidyl azide polymer (RDX/AP/GAP) intermolecular explosives (IMX) with different proportions of RDX to AP were prepared by sol‐gel method, and the structure and performance was characterized by Brunauer‐Emmett‐Teller measurements (BET), X‐ray diffraction (XRD), thermogravimetric analysis (TGA), and differential scanning calorimetry (DSC). The results showed that the specific surface area of RDX/AP/GAP IMX decreased with the addition of AP. The crystals of AP and RDX in RDX/AP/GAP intermolecular explosives were in the range of 20–48 nm and 23–55 nm, respectively. In addition, RDX/AP/GAP intermolecular explosives had the largest heat release at zero balance.     

Investigation of Energetic Particle Distribution from High‐Order Detonations of Munitions

Military training with munitions containing explosives will result in the deposition of energetic materials on ranges. These residues contain compounds that may result in human health impacts when off‐range migration occurs. Models exist that predict the spatial and mass distribution of particles, but they have proven to be difficult to apply to detonating munitions. We have conducted a series of tests to determine if modelling results can be directly applied to simple detonation scenarios. We also command detonated several rounds to obtain an initial indication of high‐order detonation particle distributional heterogeneity. The detonation tests indicate that particle distributions will be quite heterogeneous and that the model used did not adequately describe the distribution of detonation residues. This research will need to be expanded to build an empirical database sufficient to enable the refinement of existing models and improve their predictions. Research on low‐order detonations should be conducted as low‐order detonations will result in higher mass deposition than high‐order detonations. Distribution models verified with empirical data may then be incorporated into range management models.     

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.     

Degradation of TNT,RDX, and HMX Explosive Wastewaters Using Zero‐Valent Iron Nanoparticles

The high‐energy explosives 2,4,6‐trinitrotoluene (TNT), hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine (RDX), and the high melting explosive octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine (HMX) are common groundwater contaminants at active and abandoned munitions production facilities causing serious environmental problems. A highly efficient and environmentally friendly method was developed for the treatment of the explosives‐contaminated wastewaters using zero‐valent iron nanoparticles (ZVINs). ZVINs with diameters of 20–50 nm and specific surface areas of 42.56 m² g⁻¹ were synthesized by the co‐precipitation method. The explosives degradation reaction is expressed to be of pseudo first‐order and the kinetic reaction parameters are calculated based on different initial concentrations of TNT, RDX, and HMX. In addition, by comparison of the field emission scanning electron microscopy (FE‐SEM) images for the fresh and reacted ZVINs, it was apparent that the ZVINs were oxidized and aggregated to form Fe₃O₄ nanoparticles as a result of the chemical reaction. The X‐ray diffraction (XRD) and X‐ray absorption near edge structure (XANES) measurements confirmed that the ZVINs corrosion primarily occurred due to the formation of Fe₃O₄. Furthermore, the postulated reaction kinetics in different concentrations of TNT, RDX, and HMX, showed that the rate of TNT removal was higher than RDX and HMX. Furthermore, by‐products obtained after degradation of TNT (long‐chain alkanes/methylamine) and RDX/HMX (formaldehyde/methanol/hydrazine/dimethyl hydrazine) were determined by LC/MS/MS, respectively. The high reaction rate and significant removal efficiencies suggest that ZVINs might be suitable and powerful materials for an in‐situ degradation of explosive polluted wastewaters.     

Studies on Advanced RDX/TATB Based Low Vulnerable Sheet Explosives with HTPB Binder

Hydroxyl‐terminated polybutadiene (HTPB) based sheet explosives incorporating insensitive 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB) as a part replacement of cyclotrimethylene trinitramine (RDX) have been prepared during this work. The effect of incorporation of TATB on physical, thermal, and sensitivity behavior as well as initiation by small and high caliber shaped charges has been determined. Composition containing 85% dioctyl phthalate (DOP) coated RDX and 15% HTPB binder was taken as control. The incorporation of 10–20% TATB at the cost of RDX led to a remarkable increase in density (1.43→1.49 g cm⁻³) and tensile strength (10→15 kg cm⁻²) compared to the control composition RDX/HTPB(85/15). RDX/TATB/HTPB based compositions were found less vulnerable to shock stimuli. Shock sensitivity was found to be of the order of 20.0–29.2 GPa as against 18.0 GPa for control composition whereas their energetics in terms of velocity of detonation (VOD) were altered marginally. Differential scanning calorimeter (DSC) and thermogravimetry (TG) studies brought out that compositions undergo major decomposition in the temperature region of 170–240 °C.     

高品质RDX在DNAN中的溶解及反复熔融特性研究

为研究高品质RDX在2,4-二硝基苯甲醚(DNAN)中的溶解及反复熔融特性,采用高效液相色谱法研究了高品质RDX在DNAN中的溶解度及影响因素;通过工艺试验研究了DNAN/高品质RDX熔铸炸药在反复熔融后的不可逆增稠特性;运用热台显微装置研究了高品质RDX在DNAN中的溶解及析出过程,并与普通RDX(3类)进行了对比。结果表明,随着高品质RDX粒度的增大,其在DNAN中的溶解度逐渐减小,呈近似线性关系;高品质RDX在DNAN中的溶解度随温度升高而增大,115℃时高品质RDX(d50=470μm)在DNAN中的最大溶解度达到8.87g/100g,在不同温度下溶解度均小于普通RDX;DNAN/高品质RDX配方在反复熔融后的不可逆增稠程度小于DNAN/普通RDX配方;高品质RDX在DNAN中的溶解首先从晶粒的不规则外沿和晶体凹陷区域开始,溶解速率受颗粒尺寸及不规则程度影响,且明显慢于普通RDX;析出存在两种方式且析出后形状呈不规则变化。     

Estimations of Vapor Pressures by Thermogravimetric Analysis of the Insensitive Munitions IMX‐101, IMX‐104, and Individual Components

We have calculated the vapor pressures of the new explosives ordnances IMX‐101 and IMX‐104 and their respective components, 2,4‐dinitroanisole (DNAN), nitroguanidine (NQ), nitrotriazolone (NTO), and hexahydro‐1,3,5‐trinitro‐1,3,5‐triazine (RDX) by the method of rising temperature thermogravimetric analysis. Clausius‐Clapeyron relationships were assumed for each case and the vapor pressures were estimated from the Langmuir equation over an appropriate temperature range just below substance melting/decomposition points. For vapor pressures extrapolated to room temperature, the rank with respect to decreasing volatility was found to be: DNAN>IMX‐104>IMX‐101>NQ>RDX>NTO. Interestingly, vapor pressure depression is observed in IMX formulations, where the formulation has a lower vapor pressure than its most volatile component, DNAN. The enthalpy of sublimation was determined for each substance and formulation from Clausius‐Clapeyron equations generated by analysis of the thermogravimetric data. The general trends in vapor pressures and sublimation enthalpies associated with the component materials were in good agreement with previous experimental and computational results. The results obtained by this study have importance for future investigations of IMX, specifically for chemical detection and assessment of environmental fate.     

Characterization of Granular and Polymer‐Embedded RDX Grades: Floret Tests

In an attempt to further contribute to the characterization of explosive compositions, small scale Floret tests were performed using four RDX grades, differing in product quality. A Floret test provides a measure – by indentation of a copper block – of detonation spreading or the initiability and shock wave divergence and is applied in particular to explosives used in initiation trains. Both as‐received RDX and PBXs (based on the AFX‐757 composition, a hard target penetrator explosive) containing these RDX grades were tested in the Floret test set‐up. It was found that the Floret test method, when applied to granular, as‐received RDX, was not able to discriminate between the overall RDX product qualities on the basis of the resulting volume of the indentation in the copper block. For the Floret test data of the PBX samples, a division into two parts, where one of the RDX lots shows a lower dent volume compared to the other RDX lots tested. Based on the results presented in this paper with granular RDX and a PBX composition and earlier results with a different type of PBX (based on PBXN‐109, an insensitive high explosive used in a wide range of munitions), the Floret test could be developed into a screening test for shock sensitivity and product quality, without the need for complex and large volume casting of specific PBX compositions.     

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).     

From Synthesis to Formulation and Final Application

Meeting the requirements for insensitive munitions remains a complex route, where all the steps of the production process have to be addressed. NTO is a choice component, especially for large munitions. Various compositions have been optimized, which are now available, in pressed or cast PBX as well as melt cast formulations. Standard products such as RDX have been improved by the synthesis or crystallization methods, giving reduced sensitivity formulations. Some cast PBX can sustain severe shaped charge jet impacts, thanks to their large critical diameter, and are candidates as main filling of large munitions such as IM Mk82. The formulation step is addressing not only new binder principles, allowing an increase in the filler and thus energy contents, but also a bi‐component innovative method to get a semi continuous filling process where the pot life is no longer an issue. Finally a partial toolset for designing IM features is proposed with a recent example of successful application.     

Cast PBX B2238 for Small-Calibre High Performance Insensitive Munitions

Generally speaking, today's small-calibre munitions, filled with conventional melt-cast or pressed high explosives, are classified in the 1.1 or 1.2 Hazard Divisions because they explode when exposed to various threats, such as fuel fire and sympathetic detonation. The RDX-based B2238 composition is a low-cost and less sensitive cast PBX originally developed by SNPE for the initiation of cast PBX main charges. While it is easily initiated with conventional detonators, B2238 offers the same degree of insensitivity as other cast PBXs used for main charges (HEXABU 88A or OCTORANE 86B for example) and does not explode when exposed to fire and/or bullet impact. Feasibility tests carried out on several types of small-calibre munitions have shown B2238 explosive filling to be an excellent solution in the design of small calibre insensitive munitions with a high performance (in terms of fragments and shaped charge jet) comparable to that of the most energetic conventional high explosives such as 98RDX/2wax. As a result, the new IM standards, currently being defined, should allow in the future to reclassify the small-calibre munitions filled with B2238 in Hazard Divisions other than 1.1 and 1.2.     

Ageing of Australian DNAN Based Melt‐Cast Insensitive Explosives

2,4‐Dinitroanisole (DNAN) is a new melt‐cast matrix ingredient that replaces traditional TNT in TNT‐based melt‐cast explosives. Aside from sensitiveness improvements, the use of DNAN allows for the continued operation of existing melt‐cast facilities (for example the Australian Munitions plants located at Mulwala and Benalla) without the need for major plant modifications. Researchers at Defence Science and Technology Group (DST Group) have developed several DNAN based formulations that have been extensively characterized. In an effort to better understand the ageing properties of these formulations, an accelerated ageing program was undertaken. Testing was conducted under two different ageing conditions; the first test condition was conducted at a constant 60 °C with ambient humidity and the second test condition was the A2 diurnal cycle (representative of hot dry climates). Analysis of the formulation density, sensitiveness, mechanical and thermal properties was made at three‐month intervals for a period of 12 months and results compared with conventional explosives similarly aged. For all DNAN‐based formulations there was negligible change in impact, friction, electrostatic discharge, and thermal testing over time. These results highlight the ability of the ARX formulations to diurnal temperature cycling and to hold favorable sensitiveness properties to various stimuli.     

新型含能材料的研究进展

介绍了高能量密度化合物、分子间亚稳态物质、纳米结构材料等新型含能材料的研究概况以及HM X球形化和纳米结构含能复合材料方面的研究进展。研究证实,高能低感炸药得到长足发展和广泛应用,非CHNO类高能量密度材料仍处于理论探索阶段,不敏感弹药主装药中现有单质高能炸药的晶体品质得到很大提高,纳米多孔硅/硝酸盐复合材料具有较强的爆炸性质,是一类值得关注的新型含能材料。研究也获得了装填RDX纳米线的碳纳米管有序阵列,建议在新型复合含能材料方面展开广泛深入的研究。     

Thermal Decomposition,Kinetics and Compatibility Studies of Poly(3‐difluoroaminomethyl‐3‐methyloxetane) (PDFAMO)

The thermal decomposition of poly(3‐difluoroaminomethyl‐3‐methyloxetane) (PDFAMO) with an average molecular weight of about 6000 was investigated using thermogravimetric analysis (TG) and differential scanning calorimetry (DSC). The kinetics of thermolysis were studied by a model‐free method. The thermal decomposition of PDFAMO occurred in a two‐stage process. The first stage was mainly due to elimination of HF and had an activation energy of 110–120 kJ mol⁻¹. The second stage was due to degradation of the polymer chain. The Fourier transform infrared (FTIR) spectra of the degradation residues showed that the difluoroamino groups decomposed in a two‐step HF loss at different temperatures. The remaining monofluoroimino groups produced by the incomplete elimination of HF were responsible for the two‐stage thermolysis process. The compatibility of PDFAMO with some energetic components and inert materials used in polymer‐bonded explosives (PBXs) and solid propellants was studied by DSC. It was concluded that the binary systems of PDFAMO with cyclotrimethylenetrinitramine (RDX), 2,4,6‐trinitrotoluene (TNT), 2,4‐dinitroanisole (DNAN), pentaerythritol tetranitrate (PETN), ammonium perchlorate (AP), aluminum powder (Al), aluminum oxide (Al₂O₃) and 1,3‐diethyl‐1,3‐diphenyl urea (C₁) were compatible, whereas the systems of PDFAMO with lead carbonate (PbCO₃) and 2‐nitrodiphenylamine (NDPA) were slightly sensitized. The systems with cyclotetramethylenetetranitroamine (HMX), hexanitrohexaazaisowurtzitane (CL‐20), 3‐nitro‐1,2,4‐triazol‐5‐one (NTO), ammonium nitrate (AN), magnesium powder (Mg), boron powder (B), carbon black (C. B.), diphenylamine (DPA), and p‐nitro‐N‐methylamine (PNMA) were incompatible. The results of compatibility studies fully supported the suggested thermal decomposition mechanism of PDFAMO.     

Investigation of Fireball Temperatures in Confined Thermobaric Explosions

New composite metalized explosives were studied. The explosives consisted of two different types of macroscopic granular multi‐component RDX‐based formulations. In a 0.15 m³ explosion chamber, fireball temperature histories for numerous cylindrical pressed and layered charges made from the composites were determined using optical spectroscopy. For comparison, charges consisting of simple mixtures instead of the composites as well TNT and RDX phlegmatized (RDXph) charges were also studied. The influence of the structure of the macroscopic granular composite, the charge type (pressed charge or layered charge with an RDXph core), oxygen availability (air or argon atmosphere) and aluminum particle size on the fireball temperature and the combustion of the aluminum powder were determined. The measured temperatures were compared with the theoretical ones calculated by assuming different activity of the aluminum fuel.     

Preparation of Nano‐Structured RDX in a Silica Xerogel Matrix

RDX is preferred as explosive in munitions due to its balance of power and sensitivity that is known to be dependent on its particle size and size distribution. In this study, we prepared nano‐sized RDX in a silica xerogel matrix using a sol‐gel method and investigated its sensitivity for explosive properties. The presence of RDX in composite xerogel was confirmed by TG‐DSC and FTIR techniques. Microstructure and porosity were characterized by transmission electron microscopy (TEM), small angle X‐ray scattering, and N₂‐physisorption techniques. TEM results showed that the size of RDX particles in the RDX‐silica composites is in the range of 10–30 nm. The sensitivity to impact and friction was found to be higher for the composites compared to raw RDX. It was also found to be significantly dependent on the acetone/TMOS ratio used in the preparation.