Thermokinetic decomposition and sensitivity studies of 4,4ˊ-diamino-3,3ˊ-azoxy furazan (DAAF)-based melt cast explosive formulations

4,4ˊ-diamino-3,3ˊ-azoxy furazan (DAAF) is an insensitive high explosive. DAAF has safety characteristics (impact, friction) similar to triaminotrinitrobenzene and shock sensitivity similar to HMX. The present article describes the thermal analysis and sensitivity study of DAAF with RDX and 2,4,6-trinitrotoluene (TNT). DAAF has been evaluated as a possible replacement for RDX in TNT-based, aluminized as well as nonaluminized melt cast formulation. DAAF-based melt cast formulations were characterized for their sensitivity to mechanical stimuli, bomb calorimetric analysis, and thermal decomposition behavior. The thermal analysis reveals the compatibility of DAAF with benchmark explosives like RDX and TNT in explosive formulations. The composition DT (DAAF + TNT) and DTA (DAAF + TNT+ Al) is more friction and impact insensitive as compared to RT (RDX + TNT) and RTA (RDX + TNT+ Al) compositions. The bomb calorimetric values of DT composition as well as DTA composition are higher than RT and RTA compositions. The result shows that DAAF can be effectively used as a RDX replacement in melt cast explosive formulations. DT-based aluminized composition showed more thermal stability than RT- and RTA-based control compositions, which clearly revealed the usefulness of DAAF for enhanced blast effect.     

A comparative study of performance between TKX-50-based composite explosives and other composite explosives

Dihydroxylammonium 5,5′-bistetrazole-1,1′-diolate (TKX-50) is a promising candidate for high-energy explosive (e.g. HMX), which can be used as the main component in composite explosive formulations processed through a melting method. In the present study, TKX-50-based explosive composites were prepared using 2,4,6-Trinitrotoluene (TNT) or TNT/wax as the carrier, and were compared with HMX-, 3-nitro-1,2,4-triazol-5-one (NTO)-, and hexahydro-1,3,5-trinitro-1,3,5-s-triazine (RDX)-based formulations. Crystal stability, surface micro-topography, thermal decomposition performance, mechanical property, thermal sensitivity, and mechanical sensitivity of the composites were comprehensively investigated. Overall, TKX-50-based formulations exhibited improved properties with a superior safety performance compared to HMX- and RDX-based formulations and better mechanical properties than NTO-based formulations.     

Integrated rheology model: Explosive Composition B-3

ABSTRACT

Composition B-3 (Comp B-3) is a high explosive formulation composed of 60/40wt% RDX (1,3,5-trinitroperhydro-1,3,5-triazine) /TNT (2,4,6 trinitrotoluene). Above approximately 78°C this formulation partially melts to form a multiphase system with solid RDX particles in a molten TNT matrix. This multiphase system presents a number of phenomena that influence its apparent viscosity. In an earlier study explosive Composition B-3 (Comp B-3, 60/40wt% RDX/TNT) was examined for evidence of yield stress using a non-isothermal falling ball viscometer and a yield stress model was proposed. An integrated viscosity model suitable for use in computational fluid dynamics (CFD) simulations is developed to capture the transition from a heterogeneous solid to a Bingham viscoplastic fluid. This viscosity model is used to simulate the motion of imbedded spheres falling through molten Comp B-3. Comparison of the simulations to physical tests show agreement between the positions predicted by the model and the measured locations of the spheres as a function of temperature between 90C and 165C.     

Performance of a New Composite Explosive Used in Permissible Detonators for Coal Mining

A new type of composite explosive used in a permissible detonator for coal mining has been manufactured through a two-phase granulation process. The new composite explosive (NCE) contains 79–88 wt% RDX, 3–5 wt% polymer binder, 1.5–2.5 wt% insensitive agent, 6–14 wt% sodium aluminum silicate (SAS), and 1–2 wt% polyvinyl alcohol (PVA). Firstly, a water suspension granulation method was utilized to produce spherical explosive molding powder. Then, the molding powder was coated with a flame inhibitor by a spraying granulation technique. Comparatively, the molding powder provided in this work outperforms the powder manufactured from other processing in terms of fluidity, particle size distribution, flame inhibitor coating quality, and accumulation of static electricity as a result of the chemical composition and the unique granulation process. This study offers a new type of detonating explosive with improved safety and initiating ability for mining industries, and it may also provide a novel strategy for processing other types of energetic materials.     

Thermal characterization of mixtures of nitrotriazolone with HMX and RDX

Abstract

Thermal characterization of mixtures of nitrotria-zolone (NTO) with octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) has been carried out by means of differential scanning calorimetry and thermogravimetric analysis. It has been found that HMX decomposition temperature remains constant through the whole composition range. However NTO decomposition temperature decreases as the NTO/HMX ratio decreases. The RDX decomposition temperature keeps constant in all compositions studied. The RDX melting temperature decreases few degrees. The NTO decomposition appears at lower temperatures as the RDX content increases.     

Evaluation of small-scale combustion of an insensitive high explosive formulation containing 3-nitro-1,2,4-triazol-5-one (NTO), 2,4-dinitroanisole (DNAN), and 1,3,5-trinitroperhydro-1,3,5-triazine (RDX)

ABSTRACT

Energetic materials are often disposed by open-burning or open-detonation as it is a cost-effective and efficient means of destroying explosive material, and often minimizes the need to transport hazardous explosives to treatment facilities. This practice is often scrutinized for the negative environmental impact of the odorous and unsightly toxic gaseous emissions as well as the resulting deposition residues, which often contain unburned energetic materials. With the increasing use of Insensitive High Explosive compositions in munitions, it is essential that the potential environmental impact of their disposal is assessed before their extensive use to prevent the kind of contamination incidents experienced with legacy explosives. Therefore, the aim of this work was to develop a controlled laboratory experiment to identify the gaseous emissions and the energetic material residues that are generated through the combustion of the IHE components 3-nitro-1,2,4-triazol-5-one (NTO), 2,4-dinitroanisole (DNAN), and 1,3,5-trinitroperhydro-1,3,5-triazine (RDX). A sealed vial containing small (mg) quantities of energetic material was heated until the energetic material combusted. Gas chromatography/mass spectrometry (GCMS) was used to calculate the oxygen consumption and to identify the gases that were generated. The solid residues were analyzed by high-performance liquid chromatography (HPLC) to quantify unburned energetic material. Results showed that DNAN was the most resistant to burning, thus leaving significant quantities of unreacted starting material in the vial. An interesting observation for the IHE formulation was that DNAN also inhibited the combustion of NTO and RDX. The gases emitted during the open burning of IHE components and mixtures included CO, CO₂, and N₂O as expected, but the proportions differed when the components and mixture were compared, reflecting the influence of DNAN on the burning behavior. From our data, we concluded that open-burning DNAN-based formulations is an environmentally unfavorable waste-management practice for the disposal of IHEs mainly due to generation of solid residues as well as unburnt DNAN.     

Influence of Aluminum Particle Size on Thermal Decomposition of RDX

The effect of aluminum particle size (10.7 µm, 2.6 µm, and 40 nm) on the thermal decomposition of 1,3,5-trimethylene trinitramine (RDX) was investigated using differential scanning calorimetry (DSC), thermogravimetry–derivative thermogravimetry (TG-DTG), and DSC-TG–mass spectrometry (MS)–Fourier transform infrared (FTIR) spectroscopy, respectively. The results showed that the first exothermic peak (512 K) of RDX diminishes gradually with an increase in the nanosize aluminum content and is overcome by the second exothermic peak when the content of nano-Al reaches 30 wt%. The reaction mechanisms demonstrated by the nonisothermal kinetics of RDX in the absence and presence of 30 wt% Al were conformed to the Avrami-Erofeev equations for all of the RDX compositions. The nucleus growth factor for the RDX/40 nm Al mixture was found to be n = 2/3 compared to n = 3/4 for RDX with and without the microsized Al. The MS and FTIR analyses indicated that the thermal decomposition of RDX in the presence of Al nanopowders favors C-N bond cleavage over N-N bond cleavage as the rate determining step.     

Quantitative evidence for nitroso compound formation in drop-weight impacted RDX crystals

Abstract

Quantitative results are presented for the formation of two nitroso compounds during the drop-weight impact of Holston production-grade Class D RDX explosive crystals. Gas chromatography, using a sensitive Ni-63 electron capture detector, was employed to analyze “RDX residues” recovered from impact tests involving a 5 kg mass dropped from 10, 12, and 14 cm heights. The compounds, 1,3,5-trinitroso-1,3,5-triazacyclohexane (R) and 1,3-dinitroso-5-nitro-1,3,5-triazacyclohexane (RO) were detected at levels of (0·80 to 9·3) × 10^?10 percent and (1·3 to 560) × 10^?10 percent, respectively. More RO than R was formed at the 14 cm drop height. This appears to be the first time that nitroso compounds structurally similar to RDX have been observed in impacted RDX crystals.     

Evaluation of some thermal,mechanical and explosive properties of plastic bonded explosives based on epoxy resin

Abstract

RDX/HMX based Plastic Bonded Explosives (PBXs) with epoxy resin as a binder have been formulated and studied in detail for their explosive, mechanical and thermal properties. The effect of pressure on the moulding powder has also been optimized to achieve maximum loading density and compression strength. Further, these PBXs have been analysed for homogeneity and coating of binder over RDX/HMX crystals. The data suggest that epoxy resin based PBXs have higher loading density, higher mechanical strength and higher velocity of detonation (VOD) as compared to polyurethane based PBXs.     

Preparation and thermal properties study of HNIW/FOX-7 based high energy polymer bonded explosive (PBX) with low vulnerability to thermal stimulations

ABSTRACT

For modern munitions, high energy explosives are expected to reduce vulnerability and improve safety. In this study, based on the formulation of PAX-11 (94 wt% HNIW, 2.4 wt% CAB, 3.6 wt% BDNPA/F), FOX-7 is used as a portion replacement for HNIW to decrease vulnerability. To further decrease mechanical sensitivities and prevent static electricity, 0.5 wt% graphite is added to the surface of PBXs. A series of HNIW/FOX-7 based polymer bonded explosives (PBXs) with different formulations are prepared and mechanical sensitivities, thermal stabilities, detonation velocities, and slow cook-offs are studied to evaluate the energy and hazard of these PBXs. Additionally, finite element numerical simulations are utilized to study the transient temperature distributions, ignition time and ignition locations of the PBX cylinders during slow cook-off. Based on the results of this study, we obtain a high energetic low vulnerable PBX formulation (54 wt% HNIW, 40 wt% FOX-7, 2.4 wt% CAB, 3.6 wt% BDNPA/F, 0.5 wt% additional graphite) that balances energy and vulnerability. This formulation passes the slow cook-off test and detonation velocity reaches 8776 m·s^?1, which can be used in the warhead of the high explosive anti-tank cartridge.     

Effect of RDX powders on detonation characteristics of emulsion explosives

ABSTRACT

To obtain an explosive suitable for the explosive welding of foils and produce a new way to reuse demilitarized explosives, RDX powders and high amounts of hollow glass microballoons (GMs) were introduced into an emulsion matrix to reduce detonation velocity and critical thickness. The effect of different percentages of RDX on the detonation performance of the mixtures was systematically investigated. The results showed that the critical thickness decreased significantly with increasing RDX contents, and the detonation velocity at the critical thickness was almost unchanged for the different RDX contents. Thus, the as-created mixtures were suitable for the explosive welding of foils due to their low detonation velocities and low critical thicknesses. The brisance test results indicated that the brisance of the composite explosives increased with increasing RDX contents, and this trend was more remarkable at low RDX contents. All the energy output parameters of the underwater explosions also increased with increasing RDX contents.     

Electrospray Preparation and Properties of RDX/F2604 Composites

This article was an attempt to prepare energetic materials based on 1, 3, 5-trinitro-1, 3, 5-triazinane (RDX) using the electrospray method to expand its scope of application. After preparation, the morphologies and crystal structures of the samples were characterized, and thermal decomposition properties as well as mechanical sensitivities were also investigated. The sizes of the composite particles were found to be in the range of 2–4 μm. Compared with raw RDX, the crystal structures of the RDX/F2604 composites were unchanged. The activation energy of the composites was decreased with the increase of the F2604 mass ratio, and 10 wt% F2604 composites had the lowest activation energy. In the mechanical sensitivity aspect, the impact sensitivity and friction sensitivity of the RDX/F2604 composites were lower than those of raw RDX. 10 wt% F2604 composites had the highest H₅₀ (65.9 cm) and the lowest friction sensitivity (76%).     

Shock initiation of TATB/FEFO formulations

Abstract

The shock initiation properties of transferable insensitive explosive (TIE) formulations based on the solid high explosive, triaminotrinitrobenzene (TATB), and the liquid explosive, bis(2-fluoro-2,2-dinitroethyl) formal (FEFO), are measured by wedge test, embedded particle velocity gauge and embedded manganin pressure gauge techniques and calculated using the Ignition and Growth reactive flow model. These extrudable formulations are demonstrated to be slightly more shock sensitive than the TATB/inert binder explosive, LX-17. However, the TIE formulations are much less sensitive than HMX-based explosives and still qualify as insensitive explosives in safety and hazard tests. The wedge tests showed a very steep dependence of run distance to detonation on the input shock pressure. Embedded gauge and reactive flow modeling results imply that shock initiation begins when a small amount of the solid TATB decomposes rapidly enough to heat the surrounding FEFO to decomposition temperature. The FEFO then reacts rapidly, raising the pressure and temperature sufficiently to cause surface decomposition of the TATB particles at rates comparable to those measured in other TATB-based explosives. An Ignition and Growth reactive flow model for TIE based on these assumptions yields reasonable agreement with the experimental shock initiation data.     

Evaluation of the Detonation Performance of Insensitive Explosive Formulations Based on 3,3ʹ Diamino-4,4ʹ-Azoxyfurazan (DAAF) and 3-Nitro-1,2,4-Triazol-5-One (NTO)

Two energetic materials identified for relatively high energy, but little to no response to impact, spark or friction stimuli are 3-nitro-1,2,4-triazole-5-one (NTO), and 3,3? diamino-4,4?-azoxyfurazan (DAAF). More of an outlier in performance versus sensitivity, DAAF illustrates insensitivity by small-scale sensitivity tests, yet has a failure diameter estimated to be 1.25 mm and a short run length to detonation. Because of this unusual behavior, DAAF is an ideal material to formulate with NTO to obtain tailored shock sensitivity and critical diameter, with detonation velocities and pressures higher than PBX 9502. Here, we present detonation properties of Kel-F^® bonded formulations with ratios of 20–70 wt.-% DAAF added to NTO. All formulations were evaluated for detonation velocity, aluminum flyer acceleration at jump-off, and via the cylinder expansion test.     

3-Nitro-1,2,4-triazol-5-one,a less sensitive explosive

A new, less sensitive explosive has been prepared and subjected to preliminary characterization tests. The compound, 3-nitro-1,2,4-triazol-5-one (NTO) has a crystal density of 1.93 g/cm³ and calculated detonation velocity and pressure equivalent to those of RDX. Results from initial small-scale sensitivity tests indicate that NTO is less sensitive than RDX and HMX in all respects. A 4.13-cm-diam, unconfined plate-dent test at 92% of crystal density gave the detonation pressure predicted for NTO by the BKW calculation. Finally, NTO can be prepared in high yield from inexpensive starting materials.     

Ignition and Growth Modeling of Shock Initiation of Different Particle Size Formulations of PBXC03 Explosive

The change in shock sensitivity of explosives having various explosive grain sizes is discussed. Along with other parameters, explosive grain size is one of the key parameters controlling the macroscopic behavior of shocked pressed explosives. Ignition and growth reactive flow modeling is performed for the shock initiation experiments carried out by using the in situ manganin piezoresistive pressure gauge technique to investigate the influences of the octahydro-1,3,5,7–tetranitro-1,3,5,7-tetrazocine (HMX) particle size on the shock initiation and the subsequent detonation growth process for the three explosive formulations of pressed PBXC03 (87% HMX, 7% 1,3,5-trichloro-2,4,6-trinitrobenzene (TATB), 6% Viton by weight). All of the formulation studied had the same density but different explosive grain sizes. A set of ignition and growth parameters was obtained for all three formulations. Only the coefficient G₁ of the first growth term in the reaction rate equation was varied with the grain size; all other parameters were kept the same for all formulations. It was found that G₁ decreases almost linearly with HMX particle size for PBXC03. However, the equation of state (EOS) for solid explosive had to be adjusted to fit the experimental data. Both experimental and numerical simulation results show that the shock sensitivity of PBXC03 decreases with increasing HMX particle size for the sustained pressure pulses (around 4 GPa) as obtained in the experiment. This result is in accordance with the results reported elsewhere in literature. For future work, a better approach may be to find standard solid Grüneisen EOS and product Jones-Wilkins-Lee (JWL) EOS for each formulation for the best fit to the experimental data.     

Characterization and Identification of Explosives and Explosive Residues Using GC-MS,an FTIR Microscope,and HPTLC

ABSTRACT

Characterization and identification of explosives and explosive residues collected from different places in India were made using TLC, GC/EI-MS, and GC-FTIR. The explosives used were NG, PETN, TNT, tetryl, RDX, and NH₄NO₃+fuel oil. Quantitative estimation was made using HPTLC. Mass spectra of the samples using selective ion monitoring (SIM) mode based on the relative intensities of the signals X, X + 1 (intensity of the largest fragment X of the explosive, say, RDX [X = 205] was assumed to be 100%, i.e., X = 100%) show no isotopic substitution. The results were confirmed by FTIR spectra. Some physico-chemical aspects of the explosives are discussed.     

Composition Choice and Formulation of Three HMX-Based Research Explosives

The composition and formulation for three research explosives having similarities to military explosives are described. The primary energetic ingredient in each is cyclotetramethylene-tetranitramine (HMX), whose particle size is limited to a range of 125–210 μm to reduce variations in shock reactivity and performance. The binder in each explosive is hydroxy-terminated polybutadiene (HTPB). The first composition contains only these two components. Aluminum with a nominal particle size of 5 μm is incorporated into the second composition. The third composition contains ammonium perchlorate (AP) with a nominal particle size of 200 μm in addition to the aluminum. The explosives are designed with features to allow for comparisons in shock reactivity and performance and to elucidate the roles of HMX, Al, and AP.     

Particle size reduction of RDX by sequential application of solvent–antisolvent recrystallization and mechanical methods

ABSTRACT

Solvent–antisolvent recrystallization produced ~8 µm average size RDX particles (UF-RDX) that were subsequently subjected to mechanical methods of ultrasonication and ball-milling to find further achievable reduction in particle size. Long duration ultrasonication for 20 h and 300 rpm ball milling for 4 h of UF-RDX decreased its average particle size to ~2 µm. RDX produced by all the three processes (solvent–antisolvent recrystallization, ultrasonication and ball-milling) was similar to coarser RDX in structure and thermal decomposition behavior. However, UF-RDX produced by solvent–antisolvent recrystallization was significantly less impact sensitive than that produced by ball-milling and ultrasonication. The issues of residual solvent and the metal contamination during RDX processing were addressed by process parameter optimization. Solvent–antisolvent recrystallization and mechanical methods even when used sequentially could not bring average particle size of RDX to nano-scale.     

Microstructure effects on the detonation velocity of a heterogeneous high-explosive

ABSTRACT

Although numerous methods exist for the theoretical calculation of detonation parameters of explosives, few thermodynamic-hydrodynamic-based theoretical codes take into account particle size. The basis for their computational analysis is primarily focused on the equation of state of the detonation products, heat of formation, and density of the explosive composition. This study utilized regression analysis to model the relationship between the microstructure characteristics and detonation velocity of a heterogeneous high-explosive composition containing cyclotrimethylene-trinitrmaine (RDX). The principal characteristics examined were the average particle size of RDX, amount of HMX impurity within the RDX particles, method of RDX manufacture, and compositional density. Statistical analysis demonstrated the relevancy of the microstructure influence on the detonation velocity of the developed experimental compositions of 73 wt. % solids and 27 wt. % polyurethane binder. An equation is developed that accurately predicts detonation velocity based on average particle size, density, and manufacturing process for RDX. The model underscores the significance of the relationship between the average particle size and detonation velocity. Compositions containing smaller average particle sizes of RDX generate higher detonation velocities. A 100 micron increase in the average particle size was shown to decrease detonation velocity by 161 m/s for the monomodal polyurethane compositions used in this study. The relevance of using statistical models for selecting characteristics that result in optimum explosive performance is addressed.