To illustrate atomic-level insights into the physicochemical behavior of 1,1-diamino-2,2-dinitroethylene (FOX-7) under shock stimulation, this study applied pressure of 1 ​GPa–90 ​GPa on different crystalline faces through reactive molecular dynamics simulations and provided detailed information about the decomposition of FOX-7 at high pressure. The results show that the (010) face was much more compressible than the (100) face. Shocking the (010) and (100) faces yielded directional bulk moduli of 13.5 ​GPa and 29.1 ​GPa, respectively, and material sound velocities of 2.5 ​km· ​s−1 and 4.3 ​km· ​s−1, respectively. Under pressure below 60 ​GPa, the initial shock decomposition pathway of the (010) face was the intramolecular hydrogen (H) transfer, while that of the (100) face included dimerization and intermolecular H transfer. However, the difference in the reaction pathway faded away under pressure of around 80 ​GPa. Under all conditions, the main final small molecule fragments included N2 and H2O. Unlike thermal decomposition, in which FOX-7 yields NO2 via direct rupture, the high-pressure shock caused FOX-7 to produce carbon clusters with a few gaseous products.

The micro-scale detonation sequence prepared by the inkjet printing using all-liquid 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazawurtzitan (CL-20)-based energetic inks enables the micro-space fine-scale assembly and stable propagation of detonation. However, the easy crystallization and high mechanical sensitivity of all-liquid CL-20 limit its applications to the microelectromechanical system (MEMS)-based pyrotechnics. This study developed a simple micro-nano CL-20-based polyvinyl alcohol (PVA) colloidal suspension suitable for inkjet printing to control the crystal structures and mechanical sensitivities of energetic composites. The results show that the CL-20-based multilayer films formed by inkjet printing had dense microstructures, with the porosity decreasing to 13.81% and ε-type crystals. Compared with micro-nano CL-20 particles, the impact and friction sensitivities of CL-20-based multilayer films were reduced by 100% and 122%, respectively, and their apparent activation energy increased by 44.7 kJ mol−1, thus effectively improving the safety performance of micro-nano structured explosive agents. Therefore, CL-20-based multilayer films have great potential for application to the micro-scale detonation sequence of MEMS.

Using commercially available raw materials, novel pyrimidine-based energetic compounds were synthesized, namely N-(7-oxo-6,7-dihydro-[1,2,5]oxadiazolo[3,4-d]pyrimidin-5-yl)nitramide (1), 2,4,6-triamino-5-nitropyrimidin-1-ium nitrate (2), and 4,6-diamino-5-nitro-2-oxo-2,3-dihydropyrimidin-1-ium nitrate (3). They were fully characterized using NMR (1H and 13C), IR spectroscopy, and elemental analysis. The crystal structures of compounds 1 and 3 were determined using single-crystal X-ray diffraction. The decomposition temperatures of compounds 1–3 were measured to be 190.2 ​°C, 156.8 ​°C, and 234.6 ​°C, respectively. Their densities were tested to be 1.84, 1.85 ​g ​cm−3, and 1.81 ​g ​cm−3, respectively. They exhibited desirable insensitive properties, with impact sensitivity ≥15 ​J and friction sensitivity >360 ​N. In addition, the detonation performances of compounds 1–3 were calculated with detonation pressure of 26.9, 29.6 ​GPa, and 26.0 ​GPa, respectively; detonation velocity of 8089, 8644 ​m ​s−1, and 7996 ​m ​s−1, respectively). Simple synthetic processes and high performance make them potential candidates for low-sensitivity energetic materials.

In this work, a high-throughput computation (HTC) and machine learning (ML) combined method was applied to identify the determining factors of the detonation velocity (vd) and detonation pressure (pd) of energetic molecules and screen potential high-energy molecules with acceptable stability in a high-throughput way. The HTC was performed based on 1725 sample molecules abstracted from a dataset of over 106 linear nitroaliphatics with 1- to 6-membered C backbones and three types of substituents, namely single nitro group (-NO2), nitroamine (-NNO2), and nitrate ester (-ONO2). ML models were established based on the HTC results to screen high-energy molecules and to identify the determining factors of vd and pd. Compared with quantum chemistry calculation results, the absolute relative errors of vd and pd obtained using the ML models were less than 3.63% and 5%, respectively. Furthermore, eight molecules with high energy and acceptable stability were selected as potential candidates. This study shows the high efficiency of the combination of HTC and ML in high-throughput screening.

Predicting chemical properties is one of the most important applications of machine learning. In recent years, the prediction of the properties of energetic materials using machine learning has been receiving more attention. This review summarized recent advances in predicting energetic compounds’ properties (e.g., density, detonation velocity, enthalpy of formation, sensitivity, the heat of the explosion, and decomposition temperature) using machine learning. Moreover, it presented general steps for applying machine learning to the prediction of practical chemical properties from the aspects of data, molecular representation, algorithms, and general accuracy. Additionally, it raised some controversies specific to machine learning in energetic materials and its possible development directions. Machine learning is expected to become a new power for driving the development of energetic materials soon.

Additive manufacturing technology or three-dimensional (3D) printing has been applied in many manufacture fields. The combination of 3D printing and conventional energetic material fields can create sufficient space for preparing and molding of energetic materials. Although recent advances in this field are encouraging, with the printing technologies offering many merits over the traditional fabrication technologies, some application principles and material considerations should be discussed. This review summarizes some of the significant advances in this evolving field over the past few years, lists the typical application cases, discusses the current challenge, and presents the possible future development trend.

C−C linked fused triazolo-triazine with vicinal C−NH2/C−NO2 groups (4) and that with C−NH2/C−CN groups (2) were synthesized through the diazotization and cyclization of 3,3′-diamino-5,5′-bis(1H-1,2,4-triazole) with nitroacetonitrile and malononitrile, respectively. The [3 + 2] cycloaddition of the cyano group in compound 2 using sodium azide resulted in bis-triazolo-triazine with vicinal C−NH2/C−tetrazole group (3). Compounds 2–4 were characterized through infrared spectroscopy, NMR spectroscopy, and elemental analysis. Moreover, the structures of compounds 2 and 4 were confirmed through single-crystal X-ray diffraction. Remarkably, compound 4 had a density of 1.84 g·cm−3 and very high thermal decomposition temperature (349 °C, onset) and was insensitive to impact and friction (IS > 40 J, FS > 360 N). The detonation velocity and pressure of compound 4 were calculated to be 8.125 km s−1 and 26.1 GPa, respectively using EXPLO5. These results indicate that compound 4 is an excellent candidate for heat-resistant explosives.

This study investigated the influence of the wax layer on the micro-friction behavior of the energetic crystal surface by constructing the lubricating interface between wax and β-HMX crystals. The nano-scratch testing of β-HMX crystals with and without wax coating was conducted under the ramp-loading (0–3.5 ​mN) mode and the constant-loading (0.4 ​mN) mode. The testing results are as follows. Compared with the dry friction of β-HMX crystals without wax coating, wax can significantly improve the contact friction between the energetic crystals and the rigid micro-convex body. The influence of wax on the interface friction highly depends on the external load conditions. Under the ramp-loading mode, the wax layer can greatly reduce the average coefficient of friction (COF) from ∼0.7 (dry friction) to ∼0.2 (lubricating interface) and inhibit COF fluctuation. The inherent mechanism of wax reducing the interface friction works in the following way. Wax can effectively suppress the plowing effect of the rigid micro-convex body on the β-HMX crystal surface and further inhibit the occurrence of brittle fracture and crack defects. The wax layer can also suppress the friction anisotropy of the β-HMX crystal surface, significantly reducing the probability of high COF (>0.4). The distribution probabilities of COF in the range of 0–0.1 and 0–0.3 were 33% and 89%, respectively. The stick-slip effect of the friction behavior was observed under the constant-loading mode, with the COF varying periodically with the sliding distance. These study results can help understand the desensitization mechanisms of wax on the energetic crystal surface at a micro-scale quantitative level and provide a necessary basis for building the friction hot-spot model under dry friction and wax lubrication.

A novel neutral tricyclic energetic compound 5,5’ -(4-nitro-1H-pyrazole-3,5-diyl) bis (1,3,4-oxadiazol -2-amine) and a series of corresponding energetic ionic salts 7–9 were synthesized. Differential scanning calorimetry (DSC), nuclear magnetic resonance (NMR), elemental analysis, and infrared spectroscopy (IR) were used to analyze the newly synthesized compounds. Single-crystal X-ray diffraction was also used to validate the precise structure of ammonium salt 7. These energetic salts exhibit positive heat of formation (401.17 ​kJ·mol−1 to 690.66 ​kJ·mol−1), moderate detonation performance (8517 ​m·s−1 to 8803 ​m·s−1) and low mechanical sensitivity (IS ​> ​40 ​J; FS ​> ​360 ​N). It is worth noting that, in comparison to previously reported energetic salts containing nitramino 1,3,4-oxadiazole with poor thermal stability, the beginning decomposition temperatures of hydroxylamine salt 9 is greater than 180 ​°C. The newly synthesized hydroxylamine salt 9 has promise to be used as new high energy insensitive material based on the aforementioned characteristics.

Micro-sized aluminum (m-Al) has been widely used in explosives as fuel additives. Unfortunately, m-Al displays relatively long ignition delay and insufficient combustion characteristics, thus the energy can hardly be fully released in aluminized explosives. In this work, fluoropolymer coated m-Al composites were prepared by solvent evaporation method. SEM images reveal that fluoropolymer is uniformly distributed on the surface of m-Al, and most of the as-prepared particles are microspheres without apparent agglomeration. Thermal behavior results show that the presence of fluoropolymer is beneficial to the oxidation reaction of Al particles. The laser ignition experiments further confirms this conclusion. A small-scale disc acceleration experiment (DAX) was designed to evaluate the metal acceleration ability and detonation performances of CL-20 based explosives containing fluoropolymer coated m-Al composite. And the results indicate that when incorporating the fluoropolymer coated aluminum composites into explosives, the metal acceleration ability and detonation performances can be enhanced. Hopefully, the work of this paper is beneficial to the development of new methods to improve the performances of aluminized explosives.

This review provides numerous studies on nitrogen-rich tetracyclic-based heterocyclic energetic materials including oxadiazole, tetrazole, triazole, pyrazole, imidazole and tetrazine. The article mainly describes the construction method of energetic skeleton, explosive modification, and properties of tetracyclic energetic materials. The structure-property relationship was obtained by comparing the properties of a series of nitrogen-rich energetic materials. Finally, authors summarize the synthesis laws of energetic skeletons, which provides reference for the development of energetic materials in the future.

Two novel representatives of energetic (1,2,4-triazolyl)furoxans were prepared from the readily available (furoxanyl)amidrazones. Synthesized compounds were thoroughly characterized with IR and multinuclear NMR spectroscopy, elemental analysis and X-ray diffraction data. Analysis of structural features supported by quantum-chemical calculations revealed the main reasons for experimentally observed difference in thermal stability and mechanical sensitivity of both compounds. It was found that 3-cyano-4-(1H-1,2,4-triazol-3-yl)furoxan is more thermally stable (Td: 229 ​°C) than 4-azido-3-(1H-1,2,4-triazol-3-yl)furoxan (Td: 154 ​°C) and the latter compound is also more sensitive to impact and friction. In addition, both heterocyclic assemblies have high detonation parameters (vD: 7.0–8.0 ​km·s−1; p: 22–29 ​GPa) exceeding those of benchmark explosives trinitrotoluene and hexanitrostilbene which enable their usability for various energetic applications.

To improve the mechanical properties of 2,4,6-trinitrobenzene-1,3,5-triamine (TATB)-based polymer bonded explosives (PBXs), four kinds of polythiourea binders, namely the polyetherthiourea (P1), aliphatic polythiourea (P2), aromatic polythiourea (P3) and silane polythiourea (P4), were prepared and used in the PBXs. These four polythioureas were synthesized via the copolymerization of carbon disulfide (CS2) and diamines with various structures under mild conditions. They were then characterized using nuclear magnetic resonance (NMR) and Fourier-transform infrared spectroscopy (FTIR). The interfacial binding energy between polythioureas and TATB was calculated via molecular dynamics simulations. The tensile and compression mechanical properties of various PBXs (PBX-Pn, n ​= ​1–4) were studied through Brazilian and compression tests and were then compared with those of the PBX with a conventional fluoro polymer binder (PBX-FP). The results show that the PBX-P1 possessed the strongest interfacial interaction energy and the best mechanical properties among all the prepared PBXs. Its Brazilian strength and strain was 11.0 ​MPa and 0.56%, which was 89% and 256% higher than those of the PBX-FP with the same binder proportion, respectively. Furthermore, PBX-P1 showed excellent compression mechanical properties, with a compression strength of 40.7 ​MPa and a compression strain of 3.53%. Moreover, its Brazilian and compression fracture energy was 600% and 101% higher than those of PBX-FP, respectively, which was beneficial for improving the PBX stability. The results of this study provide a new idea for designing TATB-based PBX with improved mechanical properties using polyetherthiourea binders.

The microstructure of a compressed explosive solid is closely related to its shock sensitivity and mechanical properties. In this study, ultra-small-angle and small-angle X-ray scattering (USAXS and SAXS) techniques were combined to explore the hierarchical microstructure of die-pressed 2,4,6-trinitro-1,3,5-benzenetriamine (TATB) discs obtained from nanostructured TATB (nano-TATB) powder as the precursor. Using the Guinier-Porod model, the pseudo-invariants, and Porod's law, this study analyzed the microstructures of the materials on a nanometer scale to track the changes in void size, porosity, and interfacial area, which reflected the response of TATB under applied pressures of 1, 2, 5, 10, 15 kN and 30 kN. Results show that there existed three populations of voids in the measured q range. The intergranular voids with sizes of tens of nanometers were sensitive to low pressures (15 kN), as indicated by the decrease in the volume fractal dimension. Porosities of the voids with sizes of 1–900 nm, which were determined by the pseudo-invariants obtained from the scattering data, decreased from 6% to 1% as the pressures increased from 1 kN to 30 kN. The response of these structural parameters to external pressures implies that the main densification mechanisms under die compression include the flow, fracturing, and plastic deformation of the TATB granules. This study provides a direct insight into the structural evolution of TATB during compression.

Oxygen plays an important role in improving the oxygen balances and densities of energetic compounds. In this study, a series of oxygen-containing imidazo[1,2-d][1,2,4]oxadiazole building block-based energetic compounds (3–8) were synthesized and fully characterized. In addition, the structures of compounds 3–7 were determined using single-crystal X-ray diffraction. The properties of compounds were evaluated based on their density, differential scanning calorimetry, impact and friction sensitivities, heat of formation, and detonation performances. The insensitive properties of compound 6 (IS ​> ​40 ​J, FS ​> ​360 ​N) and its detonation properties (8682 ​m·s−1, 32.8 ​GPa), which are comparable to those of RDX (8795 ​m·s−1, 34.9 ​GPa), demonstrate that it is effective to improve the properties of energetic compounds by constructing oxygen-containing fused-ring backbone.

Modern trends in the development of energetic materials include the various methods of particle surface modification and the widespread use of nanosized powders. Atomic force microscopy (AFM) is a useful, but often overlooked advanced tool for the investigation of surface, subsurface, and interface properties of energetic compounds. This review highlights the diverse applications of AFM, and provides the various methods of AFM to investigate energetic materials, along with sample preparation techniques. We show that AFM has not only the value for imaging the surface, but also the capability to manipulate and perform the real experiments at the nanoscale. It could be a mechanical stimulation of the crystal and observation of the surface changes after it, or the attachment of the energetic crystal to the tipless cantilever, which approaches the polymeric sample to derive the adhesion force between two materials. We anticipate that over time the AFM-based techniques will be used more and more actively in the research of energetic materials and will benefit our better understanding of the processes taking place at interfaces and surfaces of energetic compounds.

The solid-phase ripening of nano explosives leads to the performance degradation of explosives with time, and it has been a long-standing challenge to understand the solid-phase ripening kinetics of small-molecule nanomaterials. Using an in situ atomic force microscope (AFM) and small angle X-ray scattering (SAXS), this study captured the variations in the morphology and specific surface area (SSA), respectively of hexanitrostilbene (HNS) nanoparticles, which have been applied as an advanced brisant explosive, during their ripening. The solid-phase ripening mechanisms and kinetics were discussed. Both Ostwald ripening (OR) and Smoluchowski ripening (SR) of HNS nanoparticles were observed at 60oC. This study established an empirical model to describe the decrease in SSA in 30 days, which yielded the predicted results with root mean square errors (RMSEs) lower than 5%. Moreover, it demonstrated the significant acceleration effects of dimethyl formamide (DMF) vapour on the ripening rate of HNS nanoparticles. Overall, this study may lay the foundation for scientifically predicting the long-term stability and substantially reducing the ripening rate of HNS nanoparticles and provide a methodology for the study of the solid-phase ripening of small-molecule nanomaterials.

During the last decade, energetic coordination compounds gained considerable attention due to the simple adjustments in their physicochemical properties. By combining different metal cations, energetic anions, and ligands, those compounds can be adapted for their intended use. This study used 1,5-dimethyltetrazole (3) as a highly endothermic, easily accessible, and insensitive ligand. It is a structural isomer to 1-ethyl-5H-tetrazole (1-ETZ), which was recently described as a suitable ligand. 1,5-Dimethyltetrazole was synthesized using two different methods: (1) reaction of acetone with azido (trimethyl) silane and (2) reaction of acetoxime benzenesulfonate with sodium azide. Subsequently, 1,5-dimethyltetrazole was reacted with the perchlorate salts of different 3d metals (e.g., Mn, Fe, Co, Ni, Cu, Zn) to obtain new energetic coordination compounds (ECCs). In addition, copper (II) complexes with 2,4,6-trinitro-phenolate anions were synthesized. The resultant complexes were investigated through low-temperature, single crystal diffraction experiments complemented by elemental analysis, infrared spectroscopy, and differential thermal analysis. Moreover, sensitivities towards impact and friction were investigated. In this study, all ECCs exhibited impact sensitivities between 2 and 10 ​J, friction sensitivities between 128 and 360 ​N, and thermal stabilities of up to 360 ​°C.

Abstract not available

In this study, two energetic compounds based on a 3,5-dinitropyridine backbone linked by hydrazine and imine bridges were synthesized and fully characterized using elemental analysis, NMR (1H, 13C), IR, and differential scanning calorimentry (DSC). The crystal structures of 1,2-bis(3,5-dinitropyridin-2-yl)hydrazine (2) and N-(3,5-dinitropyridin-2-yl)-6,8-dinitro-[1,2,4]triazolo[1,5-a]pyridine-2-amine (3) were further determined using X-ray diffraction. Compounds 2 and 3 possess high thermal stability, with Td of 274 ​°C and 290 ​°C, respectively, both of which are higher than 250 ​°C. In addition, both compounds have desirable insensitive properties IS ​> ​40 ​J, FS ​> ​360 ​N) and are more insensitive than HNS and PYX (HNS: IS ​= ​5 ​J, FS ​= ​240 ​N; PYX: IS ​= ​10 ​J, FS ​= ​360 ​N). Moreover, the detonation properties of compounds 2 and 3 (2: vD ​= ​7862 ​m·s−1, p ​= ​25.4 ​GPa; 3: vD ​= ​8024 ​m·s−1, p ​= ​26.9 ​GPa) are both higher than that of HNS (vD ​= ​7612 ​m·s−1, p ​= ​24.3 ​GPa). These results indicate that both compounds have promising prospects as thermostable and insensitive explosives.