Energetic Filler Research Articles

Incorporating of BCHMX in traditional plastic explosives

cis-1,3,4,6-tetranitro-octahydroimidazo-[4,5-d]imidazole (BCHMX) was investigated as an energetic filler with three different plastic explosives based on three matrices: C4 matrix, semtex10 matrix and EPX matrix. The original plastic explosives, composition C4 including RDX (1,3,5-trinitro-1,3,5-triazinane), Semtex 10 explosive based on PETN (pentaerythritoltetranitrate) and plastic RDX-silicone were included for comparison. Sensitivity and performance parameters were studied. Differential thermal analysis (DTA) was investigated to determine the thermal behavior. The sensitivities to friction and impact were evaluated and the explosive characteristics were determined by measuring the detonation velocity and determining the performance by the ballistic mortar test. The detonation parameters were also calculated for all samples using EXPLO5 code. By comparing the results obtained experimentally or by calculation, it is clear that the application of BCHMX in the used plastic matrices increases the performance and detonation characteristics in comparison with the original plastic explosives. Regarding to the results of sensitivity, thermal stability and performance tests, replacing PETN explosive by BCHMX in semtex matrices seems to form promising plastic explosive and needs further studies. On the other side, the performance of BCHMX-C4 is higher than that of composition C4.

Synthesis, characterization, testing, and detonation performance studies of fused pyrazole-based fluorescent energetic materials

Experts in the field of high energy materials strive to maintain a fine balance between energy and stability using nitrogen-rich materials and to apply sustainable development principles. Among the heterocyclic backbones, fused moieties are considered a significant backbone in energetic materials owing to their high energy content, dense nature, and stability. We have synthesized pyrazole-based fused compounds with high thermal stability, insensitivity, and moderate detonation performance to contribute to this development. All the compounds were isolated without column chromatography in one or two steps using commercially available affordable starting materials with excellent yields. Their molecular structure, crystallization, physicochemical properties, thermal stability and sensitivity behaviour were evaluated and compared with 2,4,6-trinitrotoluene (TNT), hexanitrostilbene (HNS), and 3,5-dinitro-N,N′-bis(2,4,6-trinitrophenyl) (PYX). All the compounds show acceptable detonation velocities (VOD: 7344–8068 m s−1), pressures (DP: 19–24.5 GPa), and insensitive to impact (25 - > 40 J) and friction (360 N). Among all the compounds, ammonium salt of 4-oxo-3,4-dihydropyrazolo[3,4-d] [1,2,3]triazin-6-ide (6) shows good density (1.77 g cm−3), detonation velocity (8068 m s−1) as well as 4-amino-pyrimidine 5-oxide (13) shows good physicochemical properties (d: 1.85 g cm−3, VOD: 7924 m s−1) Along with excellent insensitivity to impact and friction (35 - > 40 J and >360 N, respectively). These properties suggest that this can be a suitable replacement for benchmark explosives such as TNT, HNS, and PYX. Interestingly 4-amino-2H-pyrazolo[3,4-d]pyrimidine-5-oxide (3) exhibits fluorescence property, which can be used as a potential candidate in energetic filler or the formulations of energetic material for easy detection.

Additive manufacturing of energetic materials: Tailoring energetic performance via printing

Additive manufacturing (AM), also called three-dimensional (3D) printing, has been developed to obtain energetic materials within the past decade. 3D printing represents a family of flexible manufacturing techniques that enable fast and accurate fabrication of structures with complex 3D features and a broad range of sizes, from submicrometer to several meters. Various methods have already been explored, including templating, melting extrusion, inkjet printing and electrospray methods. It was demonstrated that the structure achieved by AM could be used to manipulate the reactivity of energetic or reactive materials by changing the flow of gases and entrained particles via architecture. By employing different AM techniques, energetic materials with controllable nanostructures and uniformly dispersed ingredients can be prepared. It is exciting to tailor the energy release without defaulting to change the formulation of the conventional method. The combustion and mechanical properties of conventional energetic materials can be retained at the same time. In this review, the preparation and characterization of AM energetic materials that have been developed in the last decade are summarized. Various AM techniques used in the fabrication of energetic materials are compared and discussed. In particular, formulations of energetic materials applied in AM, metallic fuels, binders and energetic fillers and their advantages in terms of combustion efficiency and other properties are proposed.

Novel energetic furazans containing isomeric N-(azoxy)-dinitropyrazole moieties: Synthesis, characterization and comparison of properties

Novel energetic furazans 3a–3c and 4a–4c containing isomeric (3,4-dinitro-1H-pyrazol-1-yl)-NNO-azoxy and (3,5-dinitro-1H-pyrazol-1-yl)-NNO-azoxy moieties have been obtained. A synthetic approach to aminofurazans 3a and 4a involves the reaction of 1-amino-3,4-dinitro-1H-pyrazole or 1-amino-3,5-dinitro-1H-pyrazole with 2,2,2-trifluoro-N-(4-nitrosofurazan-3-yl)acetamide and dibromoisocyanuric acid, followed by removal of the trifluoroacetyl group. Transformations of the amino group in aminofurazans 3a and 4a gave the corresponding nitro (3b, 4b) and azo (3c, 4c) substituted furazans. The compounds synthesized exhibit high experimental enthalpies of formation (2093–2847 kJ·kg−1), good thermal stabilities (onset decomposition temperatures 203–228 °C), acceptable densities (1.78–1.87 g·cm−3) and high detonation parameters (detonation velocities D = 8.71–8.99 km s−1, detonation pressures p = 33.9–38.7 GPa). Nitro substituted furazans 3b, 4b and azo substituted furazans 3c, 4c have been evaluated as effective energetic fillers for solid composite propellants, providing specific impulse values 9–11 s higher than similar formulations based on RDX and HMX, and 4–6 s higher than similar formulations based on CL-20.

Multi-scale modified nitramine crystals with conjugated structure intercalation and thin-layer catalyst coating for well-controlled energy release rate

High-energy solid propellants with lower pressure exponent, lower burn rate but with high combustion efficiency are usually desired. The use of catalysts in less amount but maintained high efficiency is essential for high-energy content and better combustion performances. The fine combination of catalyst with energetic fillers as oxidizer has been found to be a promising strategy to achieve this goal. In this paper, a widely used nitramine oxidizer, cyclotrimethylenetrinitramine (RDX) has been selected as a typical example, which was first intercalated for lower sensitivity and lower burn rate, and then it was coated with in-situ synthesized nanosized metal oxides as catalysts for lower pressure exponent using polydopamine as the interfacial binding layer. Two types of catalyst-coated hybrid RDX crystals (named as qy-RDX@Fe2O3 and qy-RDX@CuO) have been prepared and characterized. It is found that the in-situ grafted nano-Fe2O3 and CuO crystals have significant catalytic effect on qy-RDX, which increased the heat release of qy-RDX@Fe2O3 and qy-RDX@CuO from 1747 J·g−1 to 2159 J·g−1 and 2133 J·g−1, respectively. The results show that both qy-RDX@Fe2O3 and qy-RDX@CuO could reduce the ignition delay time and largely improve the burn rate of corresponding propellants at lower pressure (e.g. increased from 3.14 mm·s−1 to 5.50 mm·s−1 at 1 MPa) by coating only 0.13 wt% Fe2O3 and 0.15 wt% CuO catalysts, resulting in much lower pressure exponent (from 0.32 to 0.15). In particular, the decomposition heat of propellant containing only 10 wt% of qy-RDX@CuO is 1.5 times higher than the reference blank sample, so that its flame temperature was increased from 1800 °C to 2400 °C due to higher combustion efficiency with more energy release.

Mechanical properties of DNAN/HMX melt-cast explosive

The mechanical response and damage process of melt-cast explosives under complex stress states can be affected by having a high-volume ratio of the energetic filler material to the matrix. Understanding the characteristics of the nonlinear mechanical properties of 2,4-dinitroanisole/cyclotetramethylenetetranitramine (DNAN/HMX) melt-cast explosives with a high solid-phase content can enable the analysis of the response mechanism of different strain rates. DNAN/HMX melt-cast explosives were investigated using a universal material testing machine and a split-Hopkinson pressure bar (SHPB). The stress equilibrium and constant-strain-rate loading of the low-impedance, low-strength DNAN/HMX melt-cast explosive material in the SHPB test were achieved using an incident wave shaping technique, and stress–strain curves were obtained at different strain rates (40, 51, 110, and 256 s−1). Based on the stress–strain relationship curve of DNAN/HMX melt-cast explosives, the viscoelastic parameters of the Visco-statistical cracking mechanism (SCRAM) constitutive model of DNAN/HMX melt-cast explosives are obtained by the least squares method. The results of quasi-static and dynamic loading show that the failure stress of DNAN/HMX melt-cast explosives gradually increases with the increasing strain rate, exhibiting a significant strain rate effect, while the dynamic loading displays the viscoelastic effect. The fitted Visco-SCRAM model can better predict the mechanical response of explosives under complex loading.

Synthesis and properties of novel energetic (cyano-NNO-azoxy)furazans

Three novel energetic furazans with a cyano-NNO-azoxy group were synthesized using cyanamide and 2,2,2-tri- fluoro-N-(4-nitrosofurazan-3-yl)acetamide as the starting compounds. (Cyano-NNO-azoxy)furazans obtained display high experimental enthalpies of formation (+742 to +1073 kcal kg−1), good thermal stability (Tonset = 193–222 °C) and moderate mechanical sensitivity. These compounds may be of interest as energetic fillers in solid fuels for ramjet engines and in solid composite propellants.

Validation of CL‐20‐based Propellant Formulations for Photopolymerization 3D Printing

AbstractThe combustion performances of propellants depend on the geometry and the composition. Three‐dimensional (3D) printing or additive manufacturing provides a feasible and effective way to fabricate propellants according to interior ballistic requirements. The main objective of this paper is to improve the properties of 3D printed propellants in terms of energy content and combustion behavior. Three propellant formulas, which contain polyurethane‐acrylic acid resin as binder and hexanitrohexaazaisowurtzitane (CL‐20) as energetic filler, were fabricated by extrusion material 3D printing. The formulas with the force constant of 1107.43–1209.44 J/g were designed. The combustion behaviors of designed formulas, such as the maximum pressure, burn time, and burn rate, were characterized by closed bomb tests. Meanwhile, the curing time, printability, and inner structure of these formulas were also demonstrated to understand the 3D extrusion printing of propellants better.

Preparation and Properties of NC/TATB/Bu‐NENA/TMETN Low Sensitive Gun Propellants

AbstractSafety improvements in the field of energetic materials promoted the development of insensitive gun propellants. A low sensitive gun propellant was prepared by traditional extrusion using nitrocellulose (NC) as a binder, 1,3,5‐triamino‐2,4,6‐trinitrobenzene (TATB) as insensitive solid energetic filler, N‐butyl‐N‐nitramine (Bu‐NENA) as insensitive plasticizer, trimethylolethane trinitrate (TMETN) as co‐plasticizer, and graphite as thermal conductive filler. The density of gun propellants obtained was 1.611 g ⋅ cm−3 which was almost equaled to the theoretical density of 1.615 g ⋅ cm−3. The gun propellants exhibited excellent mechanical properties, especially cryogenic mechanical property, with the impact strength of 12.4 kJ ⋅ m−2 and the compressive strength of 157.1 MPa at −40 °C. The closed bomb test was conducted to investigate the energy and combustion performance. The results showed that the gun propellants had stable and regular combustion properties at a pressure up to 600 MPa. The burning rate pressure index n was about 1, and the impetus f and covolume α were 1045 kJ ⋅ kg−1 and 0.9764 cm3 ⋅ g−1 respectively. The vulnerabilities of the prepared gun propellants were evaluated by bullet impact, fragment impacts, sympathetic detonation, fast cook‐off, and slow cook‐off tests. The results showed that no response that was more severe than burning in test bombs was observed in bullet impact, fast cook‐off, and slow cook‐off tests under the given conditions. Moreover, a partially combustion reaction occurred in the fragment impact test with no obvious burning reaction in the sympathetic detonation test. It demonstrates that the prepared gun propellants possess good low vulnerability characteristics.

Insensitive High Explosives: V. Ballistic Properties and Vulnerability of Nitroguanidine Based Propellants

AbstractThis paper reviews the ballistic properties, stability and vulnerability of gun propellants, gas generators and rocket propellants containing nitroguanidine (NGu), CAS−No [556‐88‐7] as an energetic filler. Nitroguanidine and its formulations burn stable over a broad pressure regime extending from subatmospheric to high pressures (0.1 kPa–400 MPa). Its high nitrogen content (53.83 %) and oxygen balance (Ω=‐30.75 %) effects a high gas pressure in gun propellants combined with low explosion temperature and consequently low signature and reduced erosion. NGu is an effective stabilizer for a broad array of energetic materials encountered in gun and rocket propellants including AP, ADN, HMX, RDX, NGl and also materials with low thermal stability such as NC, HNF, TNAZ and ADN. Finally, the low vulnerability of NGu‐based propellant formulations makes them taylor made to serve insensitive munitions. This review covers 31 NGu‐based rocket and gas generating propellant formulations, 44 gun propellants, five of which contain guanylurea dinitramide, (GuDN, FOX‐12), CAS−No [217464‐38‐5] for comparison, four reference propellants containing neither of the aforementioned ingredients and six combustible cartridge case formulations based on NGu. In addition, the combustion properties of pure NGu, pure GUDN and NGu modified with 17 different catalysts are revised. The review contains 142 references from the public domain.

Silicon Nanoparticles for the Reactivity and Energetic Density Enhancement of Energetic-Biocidal Mesoparticle Composites.

Biocidal nanothermite composites show great potential in combating biological warfare threats because of their high-energy-release rates and rapid biocidal agent release. Despite their high reactivity and combustion performance, these composites suffer from low-energy density because of the voids formed due to inefficient packing of fuel and oxidizer particles. In this study, we explore the potential of plasma-synthesized ultrafine Si nanoparticles (nSi, ∼5 nm) as an energetic filler fuel to increase the energy density of Al/Ca(IO3)2 energetic-biocidal composites by filling in the voids in the microstructure. Microscopic and elemental analyses show the partial filling of mesoparticle voids by nSi, resulting in an estimated energy density enhancement of ∼21%. In addition, constant-volume combustion cell results show that nSi addition leads to a ∼2-3-fold increase in reactivity and combustion performance, as compared to Al/Ca(IO3)2 mesoparticles. Oxidation timescale analyses suggest that nSi addition can promote initiation due to faster oxygen transport through the oxide shell of Si nanoparticles. At nSi loadings higher than ∼8%, however, slower burning characteristics of nSi and sintering effects lead to an overall degradation of combustion behavior of the composites.

Mechanical Behaviour of a NTO and RDX‐Based Melt Cast Explosive

AbstractConstitutive equationsThe XF explosive family from NEXTER Munitions relies on a melt cast formulation with a TNT matrix. Melt cast formulations provide a high‐volume ratio of energetic filler material to matrix. This might affect the mechanical response of the material and its damage process. Therefore, a laboratory study has been launched to improve the knowledge of the mechanical behavior of this family of energetic materials. To mimic the conditions observed by the material inside ammunition, we chose to adapt a passive confinement method to the pyrotechnic conditions of the XF‐11585. This relies on an elastic‐perfectly plastic ring that gives us access to the shear behavior for different loadings in quasi‐static regime. This setup allowed us to investigate the physical phenomena involved under both pressure and shear. Then, based on the results obtained, we built an isotropic elastic damage model. This macroscopic modeling of damage is meant to be simple but complex enough to provide an assessment of the material degradation.

Enhancing the explosive characteristics of a Semtex explosive by involving admixtures of BCHMX and HMX

Abstract A well-known ternary plastic explosive, Czech Semtex 1H, contains a mixture of PETN and RDX softened by SBR. In this work, BCHMX was used to replace PETN in Semtex 1H to form Sem-BC+RDX. In addition, another mixture based on BCHMX and HMX as energetic fillers bonded by the polymeric matrix of Semtex 1H (Sem-BC+HMX) was studied. The particle size distribution of each individual explosive was determined to obtain the optimum mixing conditions. Friction and impact sensitivities were determined. The velocity of detonation was reported practically and the detonation properties were calculated by EXPLO5 code. The explosive strength of each sample was measured by the ballistic mortar test. The conclusion confirms that the velocity of detonation of Sem-BC+HMX was the highest in comparison with the prepared samples. Sem-BC+RDX has the least impact and frictions sensitivities. Sem-BC+RDX has higher detonation velocity, detonation properties and explosive strength than Semtex 1H. Addition of BCHMX in Semtex 1H as a replacement for PETN is the candidate to produce a high performance advanced Czech plastic explosive.

Novel, Printable Energetic Polymers

AbstractNovel, simple‐to‐make energetic mono‐ and bisvinylimidazolium perchlorate monomers are prepared and characterized. These energetic monomers offer the possibility to 3D print energetic polymers that may allow decreasing the content of the energetic filler in energetic devices without compromising their energetic properties. The new printable materials are suited for photocuring‐based additive manufacturing (AM), techniques, offering not only a large degree of control over the mechanical and energetic properties of the resulting solids, but also the production of complex geometries at high resolution.

Highly energetic nitramines: A novel platonizing agent for double-base propellants with superior combustion characteristics

The burning rate-pressure relation of solid propellant is an exponential relation; this is means catastrophic combustion process in case of sudden increase in operating pressure. This study reports on novel approach to minimize the dependence of burning rate on combustion pressure using highly energetic nitramines (RDX). Nitramine-based double base propellants with RDX content up to 20 wt% were manufactured by solventless extrusion technology. The impact of RDX content on burning rate, specific impulse, exhaust velocity, and thrust were evaluated using small-scale ballistic evaluation rocket motor. Specific impulse (Is) was enhanced by 20%. The action burning time (tb) was increased by 14%. The total thrust impulse (IFT) was significantly improved by 22%. One of the main outcomes of this study is that burning rate pressure exponent (n) was decreased significantly from 0.35 to 0.05. This novel ballistic performance finding means minimal change in burning rate with pressure variation. These findings confirmed that RDX has a dual function as energetic filler and platonizing agent. RDX blowing effect could alter the combustion mechanism by pushing the luminous flame from the burning surface. Furthermore, RDX decomposition can strengthen the platonization action. This is the first time ever to report on burning rate platonization using RDX. It can be concluded that many advantages have been achieved with one shot.

Combustion characteristics of extruded nitramine double-base propellants

AbstractThe burning rate-pressure relation of solid propellant is an exponential relation; this is means catastrophic combustion process in case of sudden increase in operating pressure. This study reports on novel approach to minimize the dependence of burning rate on the operating pressure using highly energetic nitramines (RDX). Nitramine-based double base propellants with RDX content up to 20 wt % were manufactured by solventless extrusion technology. The impact of RDX content on burning rate, specific impulse, exhaust velocity, and thrust were evaluated using small-scale ballistic evaluation rocket motor. Specific impulse (Is) was enhanced by 20 %. The action burning time (tb) was increased by 14 %. The total thrust impulse (IFT) was significantly improved by 22%. One of the main outcomes of this study is that burning rate pressure exponent (n) which was decreased significantly from 0.35 to 0.05. This novel ballistic performance means minimal change in burning rate with pressure variation. These novel findings confirmed that RDX has a dual function as energetic filler and as a platonizing agent. This is the first time ever RDX has been reported to act as a platonizing agent. It can be concluded that many advantages have been achieved with one shot.

CONTRIBUTION OF MECHANICAL ENGAGEMENT AND ENERGETIC INTERACTION IN REINFORCEMENT OF SBR-SILANE–TREATED SILICA COMPOSITES

ABSTRACT We evaluated the significance of mechanical engagement and energetic interaction between a polymer and a filler as two reinforcing mechanisms in SBR composites containing silica modified by short- and long-chain silanes. To exclude mechanical contributions of reinforcement from that of energetic contributions, surface energy of silica particles was systematically adjusted to prepare fillers of identical and diverse surface energies. Having analyzed interactions using a temperature sweep in a small-strain oscillatory test and a uniaxial tension test, results indicated that the chain length of the silane has remarkable influence on energetic filler–filler and filler–polymer interactions, but no detectable difference associated with filler–polymer mechanical engagement was observed from these experiments. However, dynamic strain sweep experiments showed that the rate of breakage of the filler network (Payne effect) is less for the composite having long-chain silane compared to that having short-chain silane. It was hypothesized that this behavior could be correlated to mechanical engagements of long-chain silanes existing on the filler structure.

Study of Advanced Plastic Bonded Explosives

Abstract: Thermochemical Properties of selected types of PBXs, based on mixtures of explosives, either classical or advanced, (RDX, HMX, PETN, CL-20 or Bicyclo-HMX) and either inert or energetic binder (HTPB or GAP), were evaluated by EXPLO5 program. PBX based on CL-20 gave the higher performance when compared with those based on RDX, HMX, PETN or Bicyclo-HMX and the compositions based on GAP have higher performance than those based on HTPB. According to the results of thermochemical calculations, PBXs samples, based on RDX and Bicyclo-HMX as energetic fillers and PU binders based on either HTPB or GAP, were selected and successfully prepared by casting technique. PBX formulations based on RDX and Bicyclo-HMX showed ignition temperature less than of pure RDX and pure Bicyclo-HMX. Furthermore, the activation energy needed for PBXs initiation decreased in presence of PU binders when compared with that of pure RDX and pure Bicyclo-HMX. The measured sensitivity characteristics proved that PBX formulation based on PU/HTPB has lower sensitivity to mechanical stimulus (impact, friction) than that of pure Bicyclo-HMX and pure RDX. The heat of combustion for PBX formulations based on PU/HTPB was higher than that based on PU/GAP. The brisance value for PBX based on PU/GAP was higher than that based on HTPB.

The Anatomy of a Pipe Bomb Explosion: Measuring the Mass and Velocity Distributions of Container Fragments

Improvised explosive devices such as pipe bombs are prevalent due to the availability of materials and ease of construction. However, little is known about how these devices actually explode, as few attempts to characterize fragmentation patterns have been attempted. In this study, seven devices composed of various pipe materials (PVC, black steel, and galvanized steel) and two energetic fillers (Pyrodex and Alliant Red Dot) were initiated and the explosions captured using high-speed videography. The video footage was used to calculate fragment velocities, which were represented as particle velocity vector maps. In addition, the fragments were weighed. The results demonstrate a correlation between the type of energetic filler and both the size and velocity of the fragments. Larger fragments were produced by Pyrodex filler indicating a less complete fragmentation, compared with smaller fragments produced by double-base smokeless powder. Additionally, higher fragment velocities were seen with Alliant Red Dot filler.

Isocyanate‐Free and Dual Curing of Smokeless Composite Rocket Propellants

AbstractTraditional composite rocket propellants are cured by treatment of hydroxyl‐terminated prepolymers with polyfunctional aliphatic isocyanates. For development of smokeless composite propellants containing nitramines and/or ammonium dinitramide (ADN), energetic binder systems using glycidyl azide polymer (GAP) are of particular interest. Polyfunctional alkynes are potential isocyanate‐free curing agents for GAP through thermal azide‐alkyne cycloaddition and subsequent formation of triazole crosslinkages. Propargyl succinate or closely related aliphatic derivatives have previously been reported for such isocyanate‐free curing of GAP. Herein, we present the synthesis and use of a new aromatic alkyne curing agent, the crystalline solid bisphenol A bis(propargyl ether) (BABE), as isocyanate‐free curing agent in smokeless propellants based on GAP, using either octogen (HMX) and/or prilled ADN as energetic filler materials. Thermal and mechanical properties, impact and friction sensitivity and ballistic characteristics were evaluated for these alkyne cured propellants. Improved mechanical properties could be obtained by combining isocyanate and alkyne curing agents (dual curing), a combination that imparted better mechanical properties in the cured propellants than either curing system did individually. The addition of a neutral polymeric bonding agent (NPBA) for improvement of binder‐filler interactions was also investigated using tensile testing and dynamic mechanical analysis (DMA). It was verified that the presence of isocyanates is essential for the NPBA to improve the mechanical properties of the propellants, further strengthening the attractiveness of dual cure systems.