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Striking a well balance between energy, sensitivity and thermostability of high performing organic materials has become a big challenge in the community of energetic materials. In the recent years, simple N-oxidation approach based on nitropyrimidine and nitropyridazine has been disclosed since the year of 1995 when nitropyrazine-N-oxides (such as LLM-105:2,6-diamino-3,5-dinitropyrazine-1-oxide) was developed, however, the development of facile N-oxidation via fused heterocylic ring is still stagnant, which has strongly limited the appearance of advanced materials. Herein, we present the specific synthesis of novel energetic materials with excellent properties in different aspects based on pyrazolium[5,1-C][1,2,4]triazine framework. Especially, for the first time we synthesized pyrazolium[5,1-C][1,2,4]triazine N-oxide, which also suggests that N-oxidation has introduced more intramolecular hydrogen bonds and resulted in larger conjugation effect at the molecular level, giving rise to an effective strategy in improving energy, safety and thermostability of energetic materials simultaneously. All compounds exhibit high densities (1.872-1.917 g·cm-3) and energetic performance (8657-8990 m·s-1). Among them, 8-nitro-3-(1H-tetrazol-5-yl)pyrazolo[5,1-c]00triazine-4,7-diamine (FPT-3) and 4-amino-7,8-dinitro-3-(1H-tetrazol-5-yl)pyrazolo[5,1-c][1,2,4]triazine-2-oxide (FPT-4) hold brilliant onset decomposition temperatures (FPT-3: Td = 335 °C; FPT-4: Td = 273 °C), good detonation properties (FPT-3: Vd = 8657 m s-1; FPT-4: Vd = 8851 m·s-1) and very low sensitivities (FPT-3: IS > 60 J, FS > 360 N; FPT-4: IS > 55 J, FS > 360 N), which indicate that both compounds are high energy explosives with very low sensitivity and excellent thermostability.

High performance, acceptable thermostability, and low mechanical sensitivity are high-demand properties in the design of competitive materials. Nitrogen-rich compounds are an alternative source of green molecules. Two simple, efficient synthetic routes to a novel material, bis (3-(trinitromethyl) − 1H-1,2,4-triazol-5-yl) methanone, 5, by using inexpensive starting compounds are described. Compound 5 has interesting chemical reactivity with water in the presence of organic solvents to form a gem diol of bis (3-(trinitromethyl) − 1H-1,2,4-triazol-5-yl) methanediol, 5a. All new molecules are well characterized by advanced spectroscopic techniques. The structures of 5·Et2O, 5a·3H2O, and salt 6 are confirmed by single-crystal X-ray analysis. The densities of the solid powder compound 5, and the crystals of 5a·3H2O were measured by a gas pycnometer. The theoretical densities and Explo5 calculations of solvent-free molecules, 5 and 5a, suggest that expanding the functionality of carbonyl-bridged compounds may be an alternative way to achieve high-performing materials.

FOX-7 demonstrates a fascinating explosophoric motif with a unique combination of detonation performance and stability. Unlike classical explosives, such as TNT, TATB, and RDX, FOX-7 exhibits superior energetic performance originating from its high density, oxygen balance, and dinitro groups. Indeed, owing to its unique energetic properties and versatile molecular structure, a variety of neutral compounds and salts have been synthesized during the past two decades and continuing. These materials comprise NH2 and NO2 groups on the C=C bond as an integral structural unit that provides an opportunity for a diverse blend of physical and detonation properties. This critical review summarizes several synthetic strategies used for structural modification of FOX-7 and highlighted their energetic properties. Due to the chemically tailorable framework, synthetic accessibilities, and superior energetic characteristics, FOX-7 is subjected to intense and expansive research and is undoubtedly considered a promising precursor for developing new explosives, propellants, and pyrotechnics.

A series of multi-functionalized 4-nitro-1,2,3-triazole based C–N linked biheterocyclic energetic compounds were synthesized using CDI (1,1′-carbonyldiimidazole) induced dehydrative cyclization. Among these energetic analogues, the representative compounds 2 and 6 exhibit great potential as melt-castable explosive (2: Tm = 72 °C , Td = 231 °C) and high-performance insensitive energetic material (6: d = 1.82 g cm−3, D = 8688 m s−1, IS > 40 J), respectively. More importantly, employing THA (O-tosylhydroxylamine) and SDIC(sodium dichloroisocyanurate), functionalized N8-branched compound (F-N8B, (E)-1,2-bis(4,5′-dinitro-2′H-[2,4′-bi(1,2,3-triazol)]-2′-yl)diazene) was synthesized via N-amination and oxidative azo coupling. In comparison to previously reported N8 type of energetic compounds, F-N8B exhibits improved impact sensitivity and friction sensitivity (IS = 7 J, FS = 72 N).

The continuous need for energetic materials with increased performance and improved safety characteristics stimulates synthetic efforts as well as physical modification of existing compounds. The present study reports the fabrication of 1,3,5,7-tetranitro-1,3,5,7-tetrazoctane (HMX)-based composites with common commercial polymers, polymethyl acrylate (PMA), acrylonitrile butadiene styrene rubber (ABS), ethyl cellulose (EC), polylactide (PLA), and polyethylene terephthalate glycol (PETG). To precipitate the polymer on the HMX particles, the supercritical CO2-based anti-solvent method was employed. Surface state studies with various modes of scanning probe microscopy show that the polymers at less than 3 wt% content do not form a continuous layer but precipitate as globular islands. Nevertheless, the coating effectively absorbs the mechanical stress, resulting in a much lower sensitivity to impact and a considerable improvement of the HMX friction sensitivity. Specifically, for HMX@3PMA composite the impact and friction sensitivities are 54 J and 240 N, as compared to 7 J and 150 N for neat HMX. Additionally, the beneficial improvement of flowability is observed for the fabricated composites, and evidenced by small-scale flow cup studies. Importantly, the suggested procedure affords the safe and easy-to-handle energetic material powder containing only 1–3 wt% of the polymer additive.

Copper azide (CA), an environmentally compatible and highly energetic material, is considered a promising primary explosive for miniaturized explosive systems. Herein, an efficient in-situ synthetic strategy was developed for fabrication of CA chips. Utilizing a nanoporous copper (NPC) chip with interconnected pores and nanoparticles as precursors, a CA chip with a large density and enhanced initiation performance was subsequently fabricated in situ from high concentration gaseous HN3. The effect of reaction time on the azide reaction was investigated, and a possible mechanism was established for the first time to explain the formation of CA. The reaction between NPC and gaseous HN3 involved a complex series of processes and included three steps. Cu reacted first with gaseous HN3 to produce Cu(N3)2, and then the Cu(N3)2 was reduced by unreacted Cu to produce CuN3. These two reactions were very fast, and copper conversion reached 87.7% after 12 min. After that, CuN3 reacted slowly with gaseous HN3 to form Cu(N3)2. Increased reaction times were beneficial for the generation of Cu(N3)2 and had an obvious influence on initiation ability. The density of CA reached 2.38 g cm−3 after 26 h. Furthermore, the CA chip was further assembled into a micro-initiation device, which successfully detonated the HNS-IV explosive. The mass of CA was less than 0.75 mg, and the thickness was 0.4 mm under the preferred conditions. CA synthesized by this method achieved the same initiation performance as the charge size was reduced to the fullest extent possible, which offers more advantages in the application of miniaturized explosive systems.

As a novel energetic material, aluminum hydride (AlH3) has attracted much attention because of its high hydrogen storage capacity and rapid dehydrogenation at low temperatures, which can be used as a promising energetic additive in solid propellants or in some other areas such as catalysts, fuel cell, and reducing agents. In particular, AlH3 as a component of solid propellant may largely promote the specific impulse of rocket engines and effectively reducing the erosion of engine nozzles. This review focuses on the research results in synthesis/regeneration, thermal decomposition, oxidation, ignition and combustion characteristics, and stabilization of AlH3 over the past decades. In particular, the stabilizing of AlH3 is essential for the its application in solid propellants, where the most widely used strategies have been introduced and compared, based on which some suggestions regarding possible future research directions are proposed.

It is the main task and challenge to reach a fine balance between high energy density and good molecular stability in energetic material research. In this study, two series of energetic compounds, 3-amino-7,7′-azo-[1,2,4] triazolo[4,3–b][1,2,4]triazole and 3,6-diamino-7,7′-azo-[1,2,4]triazolo[4,3–b][1,2,4] triazole featuring the N4 [N-N=N-N] linkage and fused triazoles, are presented. Their structures were determined by single crystal X-ray diffraction, elemental analysis, NMR, and IR spectroscopy. Their properties were studied in terms of density, thermal stability, detonation performance, and mechanical sensitivity. The N4 [N-N=N-N] linkages accord these compounds with high heat of formation, thus increasing the detonation performance. All fused triazoles exhibit planar structures, which result in low mechanical sensitivity. Through careful investigation of crystal data, strong π-π stacking and extensive hydrogen-bonding interactions were observed between molecules, which gives positive impact on mechanical sensitivity and thermal stability. The properties between different cations (or ions) were carefully studied. Quantum chemistry calculations were performed to investigate the potential relationship between structures and properties. Among them, compound 5 possesses high thermal stability (Td: 275 °C), good detonation performance (D: 8677 m s−1; P: 36.1 GPa), and excellent insensitivity (IS: 40 J; FS: 360 N), which makes it a balanced and promising energetic material.

Achieving a balanced oxidant-to-fuel ratio remains a challenge in the field of energetic materials. Now, oxygen-rich acids, H5IO6/HIO3 were combined with three weakly basic energetics (btrz: 4,4′-bis-1,2,4-triazole; atrz: 4,4′-azo-1,2,4-triazole; ICM-102: 2,4,6-triamino-5-nitropyrimidine-1,3-dioxide) to form four cocrystals (1: H5IO6/btrz; 2: H5IO6/atrz; 3: 2HIO3/atrz; and 4: HIO3/ICM-102) through the close acid-base gap of two precursors. The oxygen balances of the four cocrystals increased significantly, especially cocrystal 3, where its available oxygen atoms provided by the two HIO3 molecules is 5. Simple preparation, 49.2% iodine content, and excellent detonation performance of cocrystal 3 makes it a promising energetic biocidal agent. Cocrystal 4 shows potential as both a biocidal agent and energetic material. This work provides a new route for preparing cocrystals and broadens application of oxidants for the development of well-balanced energetic materials.

A novel fused triazolo-pyrimidine energetic compound was synthesized by the two-step diazotization-nitrification method or one-step direct nitration reaction. The physical properties and detonation properties of intermediate 3H-[1,2,3]triazolo[4,5-d]pyrimidine-5,7-diamine (2) and N-(7-oxo-6,7-dihydro-2H-[1,2,3]triazolo[4,5-d]pyrimidin-5-yl)nitramide (3) were further explored. Compound 2 has a higher decomposition temperature (368 °C) than that of 2,4,6-trinitrotoluene (TNT, 295 °C). X-ray crystal-structure analysis shows that the density of compound 3 was 1.97 g cm−3 at 100 K. Not only the detonation performance of compound 3 (8845 m s−1, 32.54 GPa) was predicted to approach RDX (8795 m s−1, 34.9 GPa) but displays significantly good safety properties (36 J), which means that compound 3 may serve as a potential high energy insensitivity material (HEIM).

Development of advanced energetic materials with promising properties has been intensely-pursued over the past decades. However, traditional strategies for integrating fuel skeleton and oxidizing groups into an organic molecule are very difficult to balance the contradictory relationship between high energy and low sensitivity of energetic materials. In this work, we present a promising approach to develop advanced energetic materials through intermolecular assembly of nitrogen-rich triazine energetic compounds and high-energy oxidants. Under the direction of electrostatic potential and proton affinity calculations, a novel energetic compound 2,4,6-triamino-1,3,5-triazine-1,3-dioxide (TTDO) was rationally designed and synthesized. The easy and effective self-assembly of TTDO with high-energy oxidants afforded a series of novel advanced energetic materials with a good balance between energy and sensitivity. Among these self-assembled energetic materials, TTDOP (a self-assembled energetic material between TTDO and HClO4) showed a very high density (2.047 g cm−3 at 100 K), detonation properties (9284 m s−1 and 41 GPa) as high as that of HMX and better mechanical sensitivity (13 J and 144 N). Moreover, TTDOP exhibited great promise as a substitute for ammonium perchlorate (AP) in solid propellant formulations due to its high combustion and propulsion performances. This work opens a new avenue to develop intermolecular energetic materials with well balanced energy & sensitivity and versatile functionality.

The limited gas production of Al/metal oxide-based thermites due to lack of gas elements (e.g., C, H, and N) greatly hinders its practical application. By contrast, energetic coordination polymers (ECPs) are rich in gas elements from organic ligands and have the potential to rapidly decompose into corresponding metal oxides with a large amount of heat output. In this work, a novel high-performance energetic material based on Al/ECPs is presented. Al/ECPs binary energetic composites have enhanced heat release, pressure production, and combustion performance owing to the contribution of the “father” ECPs’ thermal decomposition reaction and the “son” metal oxide’s thermite reaction with nano-Al. [Mn(BTO)(H2O)2]n (BTO = 1H,1′H-[5,5′-bitetrazole]-1,1′-bis(olate)) is used as a typical ECP and composited with nano-Al. The exothermic peak of the thermite reaction between 520 °C and 730 °C on the differential scanning calorimetry curves contributes to the high heat output of the Al/[Mn(BTO)(H2O)2]n energetic composites, especially when the molar ratio of Al/Mn is 1.0 (2189.6 J/g). The peak pressure of this composite (3.6 MPa) is 1.5 times as high as that of traditional nanothermite (Al/CuO) with much longer high-pressure duration in the closed bomb experiments. It also exhibits very intense burning and long duration (around 300 ms) in opening burning experiments. These results prove that the father-son effect of ECPs is highly significant in developing new-concept Al/ECPs energetic materials for gas generation, heat release and combustion.

Interface regulating is considered as a promising approach for optimizing the energy and safety performance of energetic materials (EMs). Nevertheless, realizing effective promotion of safety performance meanwhile maintaining a high energy level is still a big challenge to energetic 1,3,5,7-tetranittro-1,3,5,7-tetrazocane (HMX). Herein, novel energetic composites proposed by introducing 2,4,6 trinitrobenzene-1,3,5-triamine (TATB) at the HMX interface (denoted as HMX/TATB co-particles, cp-HMX/TATB) have been achieved by a simple hydrothermal assembly. High HMX mass contents (90%) in co-particle ensure high energy levels. Experimental and molecular dynamics simulation suggested the coupling of nitro-group in HMX and amino-group in TATB is the main driving force for the strong interfacial contact along specific crystalline directions, endowing tightly interfacial contact and assembly with low porosity. Integrated cp-HMX/TATB demonstrated enhanced crystal density and fast decomposition kinetics. Moreover, resultant energetic cp-HMX/TATB deliver superior Bundesanstalt-fur-Materialforschung (BAM) sensitivities (impact: 65 J, friction: 288 N) amongst reported HMX-based EMs and much improved detonation velocity and pressure of 9173.35 m s−1 and 39.65 GPa, respectively, indicating a combination of efficient desensitization and high energy level. Detailed understanding of the interface properties in high-energy explosives generated by the interfacial engineering sheds lights on the design of efficient energetic material system with high energy and favorable safety.

The barrier in the development of energetic material is the material design and performance improvement based on it. Currently, creative design and preparation of novel nitrogen-rich compounds are significant for new generation of green energetic materials. At the present work, organic heterocyclic hybrid pyrazol-triazole was constructed, synthesized and applied as building blocks in the development of versatile thermally stable high-energy materials. All derivatives were fully characterized by vibrational infrared spectroscopy (IR), multinuclear NMR (1H, 13C) spectroscopy, elemental analysis, differential scanning calorimetry (DSC), impact and friction-sensitivity test. Additionally, the structures of 4–8 and 10–13 were further confirmed by single-crystal X-ray diffraction and their crystal packing characteristics were thoroughly analyzed. Compound 2 not only enchanced physical properties of its ionic derivatives obviously, but also showed good detonation performance (D: 9075 m s−1) exceeding that of RDX, excellent insensitivity (IS > 80 J, FS > 360 N) comparable to that of TATB and superior thermal stability (331 °C) to that of HNS. Its ionic salts (compounds 4–14) also exhibit reasonable properties, such as good experimental densities (1.75–2.10 g cm−3), high thermal stability (174289 °C), good safety properties, excellent detionation performance (Dv: 7745–8952 m s−1, P: 23.830.6 GPa), suggesting this new pyrazol-triazole hybrid is beneficial for improving their physical performance. This work is helpful for accelerating the discovery of insensitive, thermostable and high-energy green energetic materials.

Melamine–formaldehyde resins (MF resins) were selected for the fabrication of three typical nitramine explosives (cyclotrimethylenetrinitramine, RDX; cyclotetramethylenetetranitramine, HMX; and hexanitrohexaazaisowurtzitane, CL-20) based microcapsules, the polymer coating shell could be prepared via a facile in situ polymerization of melamine and formaldehyde on the surface of explosive crystals. Structural characterizations and thermal properties of the core–shell composites were systematically studied by scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), fourier-transform infrared (FT-IR) spectra and differential scanning calorimeter (DSC). The SEM and XPS results indicated that these three energetic cores were mostly well coated. XRD and FTIR analyses showed the combined characteristics of explosives and MF resins, and revealing that the polymorph of CL-20 maintained the optimal e form during the whole preparing process. After coating, the endothermic polymorphic phase transition as well as the exothermic thermal decomposition temperature of the explosives was visibly increased, attributing to the outstanding heat resistance of MF resin shell. The impact sensitivity of the resultant microcapsules could be reduced from 2 to 3 times, depending on energetic material, after coating by 3 wt% MF resins.

Although ammonium nitrate (AN) is a clean burning (chlorine free), non-corrosive, low-hazard, low-flame temperature, inexpensive, easily available energetic material and gives maximum gas horse power per unit weight, propellants incorporating AN suffer from three significant drawbacks: (1) polymorphic (phase) transition near ambient temperature, (2) caking and smoke generation upon burning, and (3) poor flowability for packing. The first two disadvantages could be minimized by forming non-hygroscopic, smokeless 1:1 co-crystals of ammonium nitrate–benzo-18-crown-6 (1:1 co-crystals of AN–B18C6) with a melting point of 125–129 °C, produced from the antisolvent precipitation method based on the systems of: ethanol–methyl-tert-butyl-ether (MTBE), methanol–ethyl acetate and methanol–MTBE. From the smoke test and burning characteristics, 1:1 co-crystals of AN–B18C6 is smokeless upon heating and exhibits a slower burning rate than the one of AN. Therefore, co-crystallization may become a solid-state modification method in the areas of propellants and explosives. The third drawback could further be eliminated by forming spherical agglomerates of 1:1 co-crystals of AN–B18C6 through the addition of water as a bridging liquid into the co-crystal slurry resulted at the end of the antisolvent precipitation method. Spherical agglomerates of 1:1 co-crystals of AN–B18C6 grown from Phase IV AN powders (0.32 mmol) and B18C6 crystals (0.32 mmol) in 0.64 mL methanol + 11.6 mL MTBE + 0.08 mL water gave relatively high yield of 87.3%, high population density of 20.6/cm3, high sphericity, of 0.86, high friability of 100 showing a greater strength, and low angle of repose of 25.2° indicating a good flowability.