Insensitive Munitions Research Articles

Formulation development and characterization of cellulose acetate nitrate based propellants for improved insensitive munitions properties

Cellulose acetate nitrate (CAN) was used as an insensitive energetic binder to improve the insensitive munitions (IM) properties of gun propellants to replace the M1 propellant used in 105 mm artillery charges. CAN contains the energetic nitro groups found in nitrocellulose (NC), but also acetyl functionalities, which lowered the polymer's sensitivity to heat and shock, and therefore improved its IM properties relative to NC. The formulation, development and small-scale characterization testing of several CAN-based propellants were done. The formulations, using insensitive energetic solid fillers and high-nitrogen modifiers in place of nitramine were completed. The small scale characterization testing, such as closed bomb testing, small scale sensitivity, thermal stability, and chemical compatibility were done. The mechanical response of the propellants under high-rate uni-axial compression at, hot, cold, and ambient temperatures were also completed. Critical diameter testing, hot fragment conductive ignition (HFCI) tests were done to evaluate the propellants' responses to thermal and shock stimuli. Utilizing the propellant chemical composition, theoretical predictions of erosivity were completed. All the small scale test results were utilized to down-select the promising CAN based formulations for large scale demonstration testing such as the ballistic performance and fragment impact testing in the 105 mm M67 artillery charge configurations. The test results completed in the small and large scale testing are discussed.

Study on the Structures of Two Booster Pellets Having High Initiation Capacity

Insensitive munitions (IM) improve the survivability of both weapons and their associated platforms, which can lead to a reduction in casualties, mission losses, and whole life costs. All weapon systems contain an explosive train that needs to meet IM criteria but reliably initiate a main charge explosive. To ensure that these diametrically opposed requirements can be achieved, new highly effective booster charge structures were designed. The initiation capacity of the two booster pellets was studied using varied composition and axial-steel-dent methods. The results showed that the two new booster pellets can initiate standard main charge pellets with less explosive mass than the ordinary cylindrical booster pellet. The numerical simulation results were in good agreement with the experiment results.

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

Abstract2,4‐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.

Analysis of munitions constituents in IMX formulations by HPLC and HPLC–MS

The use of Insensitive Munitions eXplosives (IMX) is increasing as the Army seeks to replace certain conventional munitions constituents, such as 2,4,6-trinitrotolene (TNT), for improved safety. The IMX formulations are more stable and therefore less prone to accidental detonation while designed to match the performance of legacy materials. Two formulations, IMX 101 and 104 are being investigated as a replacement for TNT in artillery rounds and composition B Army mortars, respectively. The chemical formulations of IMX-101 and 104 are comprised of four constituents;2,4-dinitroanisole (DNAN), 3-nitro-1,2,4-triazol-5-one (NTO), 1-nitroguanidine (NQ), and Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) which are mixed in various ratios to achieve the desired performance. The current work details the analysis of the IMX constituents by single column HPLC–UV–ESI-MS. Detection limits determined are in agreement with similar HPLC analysis of compounds, ranging from 7 to 9μg/L. Gradient mobile phases are used to allow separation of the 4 target compounds in more complex mixture of other concomitant compounds. Mass spectra are used to confirm analyte identity with chromatographic retention time.

Algal growth stimulation and toxicity in response to exposure to the new insensitive military high‐nitrogen energetic triaminoguanidinium‐1‐methyl‐5‐nitriminotetrazolate

Triaminoguanidinium-1-methyl-5-nitriminotetrazolate (TAG-MNT) is a nitrogen-rich energetic compound being developed as a potential component of insensitive munition formulations. The purpose of the present study was to assess the toxicity of TAG-MNT to the green alga Pseudokirchneriella subcapitata as well as to determine whether the high N content of TAG-MNT could result in increased algal growth in aquatic systems and potentially contribute to eutrophication using a 96-h algal growth bioassay in N-limited test media. Results were compared with algal exposures to current-use energetics 2,4,6-trinitrotoluene (TNT) and royal demolition explosive (RDX). The TNT exposure resulted in a lowest-observed-adverse-effect concentration (LOAEC) for algal growth of 1.72 mg/L and a 50% inhibition concentration (IC50) and 95% confidence limits of 0.972 mg/L (0.955, 0.973). The RDX algal growth LOAEC was 0.10 mg/L, and the RDX IC50 was 0.635 (0.416, 0.875). Neither TNT nor RDX exposure resulted in stimulation of algal growth. In repeated testing, TAG-MNT exposure resulted in LOAECs of 0.55 and 5.20 mg/L. Stimulation of algal growth was observed at 0.06 mg/L at a mean increase of 163.2% (± 71.7) relative to the control in TAG-MNT test A and at the 0.005 mg/L treatment at a mean increase of 174.3% (± 59.9) in TAG-MNT test B. The authors' results indicate the potential for high-N energetics to significantly stimulate algal growth at low concentrations in N-limited systems.

TOWARD HIGH-PERFORMANCE, GREENER, AND LOW-VULNERABILITY MUNITIONS WITH THE RIGHTTRAC TECHNOLOGY DEMONSTRATOR PROGRAM

The revolutionary insensitive, green, and healthier training technology with reduced adverse contamination (RIGHTTRAC) program is a 5-year technology demonstration program (TDP) aimed at showing that green and insensitive munitions have better properties than current munitions, and that it is feasible to implement safer weapon solutions that would ease the environmental pressure on ranges and training areas and decrease the health hazards for the users. The goals of this TDP are to reach a near-zero dud rate and to eliminate the potential for research development explosive (RDX) contamination as well as the use of toxic and carcinogenic compounds. This will be done by performing significant improvements to the fuzing system, the main explosive charge and the gun propellant. The vehicle used for this demonstration is a 105-mm army artillery munition (high-explosive M1), currently filled with Composition B (a 60:40 RDX:TNT mix) and using a single-base gun propellant (M1 formulation). The aim of this communication is to provide an overview of the project and to describe the steps taken to evaluate the environmental properties of the chosen propellant and explosive formulations. At its completion, it is believed that this project will have provided the required data to assess the long-term effects of the munitions on the environment right at an early stage of the weapon development cycle, and that this can be cost effective in the long run. This will help sustain military training while preserving our resources, as well as shaping the future of weapon system development.

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

AbstractWe 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.

친환경 산화제 GUDN의 효율적 합성

Guanylurea-dinitramide(GUDN)는 낮은 감도와 좋은 성능을 가진 에너지 물질로서 추진제 및 둔감 탄약에 사용할 수 있다. 고에너지 고밀도 화약인 GUDN의 효과적인 합성과 특성분석을 이화학적 분석 및 원소분석을 통하여 수행하였다. Gaussian 09 프로그램을 사용하여 생성열을 계산하였다. 화약의 안전한 취급을 위해서 충격 및 마찰 감도를 BAM 방법으로 측정하였다. N-Guanylurea dinitramide (GUDN) is an energetic material with low sensitivities and good performance for use as propellants or insensitive munitions explosives. The efficient synthesis and characterization of high energy density material of GUDN is reported. GUDN was characterized spectroscopically as well as elemental analysis. In addition, the heats of formation were calculated with the Gaussian 09 suite of programs. For initial safety testing, the impact sensitivity and the friction sensitivity were tested following BAM procedure.

Energetic Residues from the Detonation of IMX‐104 Insensitive Munitions

AbstractThe 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.

Silicon Fuel in High Performance Explosives

AbstractIn an effort to improve the insensitive munition (IM) response but maintain performance of aluminized formulations, silicon was investigated as a possible replacement for aluminum. An RDX‐based silicon explosive was developed in which nearly 90 % reaction of silicon to silicon dioxide was realized by 7 volume expansions as measured by the 2.54 cm diameter copper cylinder expansion test. In spite of the low nitramine loading in the formulation (79 wt.‐%), the corresponding Gurney constant for the explosive was 2.81±0.02 km s−1, which is superior to Composition A‐3 under the same experimental conditions (91 % RDX, 2.69±0.02 km s−1). Energy calculations from detonation calorimetry also indicate reaction of the silicon, which was further confirmed by both silicon metal and silicon dioxide in the analyzed residue. The energy release, despite it being equivalent to a highly loaded explosive, was found to lag behind the rate of A‐3. This indicates silicon oxidation may occur sometime after lighter gas reactions in the reaction front, but is fast enough to impart work in the copper cylinder test.

Microbial toxicity of the insensitive munitions compound, 2,4-dinitroanisole (DNAN), and its aromatic amine metabolites

2,4-Dinitroanisole (DNAN) is an insensitive munitions compound considered to replace conventional explosives such as 2,4,6-trinitrotoluene (TNT). DNAN undergoes facile microbial reduction to 2-methoxy-5-nitroaniline (MENA) and 2,4-diaminoanisole (DAAN). This study investigated the inhibitory effect of DNAN, MENA, and DAAN toward various microbial targets in anaerobic (acetoclastic methanogens) and aerobic (heterotrophs and nitrifiers) sludge, and the bioluminescent bacterium, Aliivibrio fischeri, used in the Microtox assay. Aerobic heterotrophic and nitrifying batch experiments with DAAN could not be performed because the compound underwent extensive autooxidation in these assays. DNAN severely inhibited methanogens, nitrifying bacteria, and A. fischeri (50% inhibitory concentrations (IC50) ranging 41–57μM), but was notably less inhibitory to aerobic heterotrophs (IC50>390μM). Reduction of DNAN to MENA and DAAN lead to a marked decrease in methanogenic inhibition (i.e., DNAN>MENA≈DAAN). Reduction of all nitro groups in DNAN also resulted in partial detoxification in assays with A. fischeri. In contrast, reduction of a single nitro group did not alter the inhibitory impact of DNAN toward A. fischeri and nitrifying bacteria given the similar IC50 values determined for MENA and DNAN in these assays. These results indicate that reductive biotransformation could reduce the inhibitory potential of DNAN.

Ecotoxicological assessment of a high energetic and insensitive munitions compound: 2,4-Dinitroanisole (DNAN)

The high explosive nitroaromatic 2,4-dinitroanisole (DNAN) is less shock sensitive than 2,4,6-trinitrotoluene (TNT), and is proposed as a TNT replacement for melt-cast formulations. Before using DNAN in munitions and potentially leading to environmental impact, the present study examines the ecotoxicity of DNAN using selected organisms. In water, DNAN decreased green algae Pseudokirchneriella subcapitata growth (EC50=4.0mg/L), and bacteria Vibrio fischeri bioluminescence (Microtox, EC50=60.3mg/L). In soil, DNAN decreased perennial ryegrass Lolium perenne growth (EC50=7mg/kg), and is lethal to earthworms Eisenia andrei (LC50=47mg/kg). At sub-lethal concentrations, DNAN caused an avoidance response (EC50=31mg/kg) by earthworms. The presence of DNAN and 2-amino-4-nitroanisole in earthworms and plants suggested a role of these compounds in DNAN toxicity. Toxicity of DNAN was compared to TNT, tested under the same experimental conditions. These analyses showed that DNAN was equally, or even less deleterious to organism health than TNT, depending on the species and toxicity test. The present studies provide baseline toxicity data to increase the understanding of the environmental impact of DNAN, and assist science-based decision makers for improved management of potential DNAN contaminated sites.

Insights into the dissolution and the three-dimensional structure of insensitive munitions formulations

Two compounds, 2,4-dinitroanisole (DNAN) and 3-nitro-1,2,4-triazol-5-one (NTO) are the main ingredients in a suite of explosive formulations that are being, or soon will be, fielded at military training ranges. We aim to understand the dissolution characteristics of DNAN and NTO and three insensitive muntions (IM) formulations that contain them. This information is needed to accurately predict the environmental fate of IM constituents, some of which may be toxic to people and the environment. We used Raman spectroscopy to identify the different constituents in the IM formulations and micro computed tomography to image their three-dimensional structure. These are the first three-dimensional images of detonated explosive particles.For multi-component explosives the solubility of the individual constituents and the fraction of each constituent wetted by water controls the dissolution. We found that the order of magnitude differences in solubility amongst the constituents of these IM formulations quickly produced hole-riddled particles when these were exposed to water. Micro-computed tomography showed that particles resulting from field detonations were fractured, producing conduits by which water could access the interior of the particle. We think that micro-computed tomography can also be used to determine the initial composition of IM particles and to track how their compositions change as the particles dissolve. This information is critical to quantifying dissolution and developing physically based dissolution models.

Joint Photomicrobial Process for the Degradation of the Insensitive Munition N-Guanylurea-dinitramide (FOX-12)

N-Guanylurea-dinitramide (FOX-12) is a very insensitive energetic material intended to be used in the composition of next-generation insensitive munitions. To help predict the environmental behavior and fate of FOX-12, we conducted a study to determine its photodegradability and biodegradability. When dissolved in water, FOX-12, a guanylurea-dinitramide salt, also named GUDN, dissociated instantly to produce the dinitramide moiety and guanylurea, as demonstrated by high-performance liquid chromatography (HPLC) analysis. When an aqueous solution of FOX-12 was subjected to photolysis using a solar-simulated photoreactor, we found a rapid removal of the dinitramide with concurrent formation of N₂O, NO₂(-), and NO₃(-). The second component, guanylurea, was photostable. However, when FOX-12 was incubated aerobically with the soil isolate Variovorax strain VC1 and protected from light, the dinitramide component of FOX-12 was recalcitrant but guanylurea degraded effectively to ammonia, guanidine, and presumably CO₂. When FOX-12 was incubated with strain VC1 in the presence of light, both components of FOX-12 degraded, giving similar products to those described above. We concluded that the new insensitive explosive FOX-12 can be effectively degraded by a joint photomicrobial process and, therefore, should not cause persistent contamination of surface waters.

Pathways of reductive 2,4‐dinitroanisole (DNAN) biotransformation in sludge

As the use of the insensitive munition compound 2,4-dinitroanisole (DNAN) increases, releases to the environment may pose a threat to local ecosystems. Little is known about the environmental fate of DNAN and the conversions caused by microbial activity. We studied DNAN biotransformation rates in sludge under aerobic, microaerophilic, and anaerobic conditions, detected biotransformation products, and elucidated their chemical structures. The biotransformation of DNAN was most rapid under anaerobic conditions with H2 as a cosubstrate. The results showed that the ortho nitro group in DNAN is regioselectively reduced to yield 2-methoxy-5-nitroaniline (MENA), and then the para nitro group is reduced to give 2,4-diaminoanisole (DAAN). Both MENA and DAAN were identified as important metabolites in all redox conditions. Azo and hydrazine dimer derivatives formed from the coupling of DNAN reduction products in anaerobic conditions. Secondary pathways included acetylation and methylation of amine moieties, as well as the stepwise O-demethylation and dehydroxylation of methoxy groups. Seven unique metabolites were identified which enabled elucidation of biotransformation pathways. The results taken as a whole suggest that reductive biotransformation is an important fate of DNAN leading to the formation of aromatic amines as well as azo and hydrazine dimeric metabolites.

Shaped Charge Jet Characterization and Initiation Test Configuration for IM Threat Testing

Rocket propelled grenade (RPG) shaped charge attack threats are of particular concern for Insensitive Munitions (IM) development. In response to these threats, the U.S. Project Engineering Office for Ammunition (PEO Ammo) have worked with the U.S. Army Armament Research, Development and Engineering Center (ARDEC) Energetics and Warheads Division (EWD) to develop a highly reproducible and well characterized standardized 81mm shaped charge jet initiation test configuration. This 81mm shaped charge and jet attack configuration is used to determine whether an acceptable explosion or lower level response is observed. The test is completed as per STANAG 4526. The 81mm shaped charge is comprised of a high precision forged and machined liner made from C101 Oxygen Free Copper (OFE, UNS C10100) and a bare billet LX-14 pressed billet configuration that is machined to final dimensions. This warhead choice overcomes the issue of testing variability observed if actual production RPGs are used for Insensitive Munitions (IM) threat testing. The test configuration includes an aluminum buffer plate that is used to condition the jet for desired jet characteristics, as well as a representation for RPG probe position. Modeling and simulation was used to develop the shaped charge and test configuration. The resulting configuration has been experimentally characterized using flash radiography for short and long stand-off in order to provide quantified jet characterization including velocity profiles, accumulated length, accumulated mass, jet diameter and v2d profiles. The result is a simple reproducible test configuration that represents an RPG attack geometry. The test configuration has been adopted by the U.S. DoD for RPG IM threat testing and has been used on a large variety of munition test articles.

Photochemical transformation of the insensitive munitions compound 2,4-dinitroanisole

The insensitive munitions compound 2,4-dinitroanisole (DNAN) is increasingly being used as a replacement for traditional, sensitive munitions compounds (e.g., trinitrotoluene [TNT]), but the environmental fate and photo-transformation of DNAN in natural water systems are currently unknown. In this study, we investigated the photo-transformation rates of DNAN with both ultraviolet (UV) and sunlight irradiation under different environmentally relevant conditions. Sunlight photo-transformation of DNAN in water was found to follow predominantly pseudo-first-order decay kinetics with an average half-life (t1/2) of approximately 0.70d and activation energy (Ea) of 53kJmol−1. Photo-transformation rates of DNAN were dependent on the wavelength of the light source: irradiation with UV-B light (280–315nm) resulted in a greater quantum yield of transformation (ϕUV-B=3.7×10−4) than rates obtained with UV-A light (ϕUV-A=2.9×10−4 at 316–400nm) and sunlight (ϕsun=1.1×10−4). Photo-oxidation was the dominant mechanism for DNAN photo-transformation, based on the formation of nitrite (NO2−) and nitrate (NO3−) as major N species and 2,4-dinitrophenol as the minor species. Environmental factors (e.g., temperature, pH, and the presence or absence of naturally dissolved organic matter) displayed modest to little effects on the rate of DNAN photo-transformation. These observations indicate that sunlight-induced photo-transformation of DNAN may represent a significant abiotic degradation pathway in surface water, which may have important implications in evaluating the potential impacts and risks of DNAN in the environment.

1,1-Diamino-2,2-dintroethene (FOX-7) nanocrystals embedded in mesoporous carbon FDU-15

Insensitive energetic materials are considerably desirable for insensitive munitions or low vulnerability ammunition compositions because of the reduced risks involved with their use. The ability to control compositions and properties for such materials is also of interest since it can lead to optimal performance, controlled energy release, and low sensitivity. With these goals in mind, we focus our work on a high energy density material, 1,1-diamino-2,2-dinitroethylene (FOX-7). FOX-7 nanocrystals under confined conditions are synthesized in mesoporous carbon FDU-15 through self-assembly. Complete impregnation can be achieved in N-methyl-2-pyrrolidone at 100–110°C, and the maximum amount of FOX-7 in the FOX-7/FDU-15 composites is around 43.8wt.% (C-43.8). Host–guest interactions are investigated by wide-angle XRD, 13C solid-state NMR, and FT-IR. C-43.8 shows low phase transition temperature and fast thermal decomposition rate compared with bulk FOX-7 crystals and the physical mixture. The host–guest structure of the composites demonstrates a novel and efficient space-insensitivity concept. C-43.8 shows no sensitivity toward both friction and impact, and insensitive to electrostatic spark (V50>37kV; E50>20J). The extreme insensitivity is closely related to the high thermal and mechanical stability of FDU-15.

Thermal Decomposition and Ignition of PBXN-110 Plastic-Bonded Explosive

Due to safety requirements, insensitive behavior in slow or fast thermal heating (cook-off) conditions is a desired behavior for today’s munitions. The ignition time of munitions under slow or fast cook-off conditions is an important parameter in the design of insensitive munitions. The critical temperature, which mainly depends on the chemical, physical, and the geometrical properties of the energetic material, is the determining factor whether the material will end up with thermal initiation or not, when it is exposed to an external heat source. In this study a slow cook-off test setup is designed and developed and the tests for a generic munition containing PBXN-110 plastic-bonded explosive are performed in order to obtain temperature distribution in the test item, ignition time, ignition temperature, and ignition location. In this paper the development procedure and the experimental results of the slow cook-off tests are explained. Moreover, the kinetic parameters such as activation energy and pre-exponential factor for the plastic-bonded explosive obtained from the TGA tests are presented.

Investigating the Mechanical Properties of RDX Crystals Using Nano‐Indentation

AbstractThe shock sensitivity of RDX is of major interest for the development of insensitive munitions. Previous research has implied that internal defects that form within RDX crystals have a strong sensitising effect, increasing the probability of shock initiation. During the NATO Reduced sensitivity RDX Round Robin (R4) program the number of internal defects within RDX crystals of differing qualities were assessed by optical microscopy and a scoring system. The results suggested that RDX crystals with many internal defects were more sensitive. Studies investigating the mechanical properties of bulk RDX have shown that lots consisting of poorer crystals are weaker. This study investigates the mechanical properties of individual crystals from different RDX lots using nano‐indentation. It is shown that crystals with many internal defects have reduced modulus of elasticity, stiffness and prone to greater deformation under applied load. The results also show a correlation between these parameters and previously reported shock sensitivity data.