High-performance Energetic Materials Research Articles

First Alliance of Pyrazole and Furoxan Leading to High-Performance Energetic Materials.

Nitrogen heterocyclic scaffolds retain their leading position as valuable building blocks in material science, particularly for the design of small-molecule energetic materials. However, the search for more balanced combinations of directly linked heterocyclic cores is far from being exhausted and aims to reach ideally balanced high-energy substances. Herein, we present the synthetic route to novel pyrazole-furoxan framework enriched with nitro groups and demonstrate a promising set of properties, viz., good thermal stability, acceptable mechanical sensitivity, and high detonation performance. In-depth crystal analysis showed that the isomers having lower-impact sensitivity values in both types of regioisomeric pairs are those with the exocyclic furoxan oxygen atom being closer to the pyrazole ring. Owing to the favorable combination of high crystal densities (1.83-1.93 g cm-3), positive oxygen balance to CO (up to +13.9%), and high enthalpies of formation (322-435 kJ mol-1), the synthesized compounds show high calculated detonation velocities (8.4-9.1 km s-1) and excellent metal accelerating abilities. The incorporation of the 3-nitrofuroxan moiety increases the thermal stability (by ca. 20 °C) and decreases the mechanical sensitivity of target hybrid materials in both types of regioisomeric pairs. Simultaneously, the detonation performance of 3-nitrofuroxans is almost identical to that of 4-nitrofuroxans, highlighting the potential of the regioisomeric tunability in the future design of energetic materials.

Construction of Nitrogen-Rich Energetic Isomers Containing Multiple Hydrogen Bond Networks.

Nitrogen-rich energetic materials have been the focus of a few studies on their isomers. Novel nitrogen-rich energetic compounds TZ, DTZ, and NTZ were synthesized through simple steps. The hydrogen bond networks significantly enhanced their properties (TZ, Td = 290 °C and Dv = 8370 m s-1; DTZ, Td = 282 °C and Dv = 8392 m s-1; and NTZ, Td = 272 °C and Dv = 8762 m s-1), which are superior to their isomers. This realized a balance between the energy and stability of polycyclic tetrazoles, providing insights for high-performance energetic materials.

Synthesis and Study of Steering of Azido-tetrazole Behavior in Tetrazolo[1,5-c]pyrimidin-5-amine-Based Energetic Materials.

Tetrazoles and their derivatives are essential for compound synthesis due to their versatility, effectiveness, stability in air, and cost-efficiency. This has stimulated interest in developing techniques for their production. In this work, four compounds, tetrazolo[1,5-c]pyrimidin-5-amine (1), N-(4-azidopyrimidin-2-yl)nitramide (2), tetrazolo[1,5-c]pyrimidin-5(6H)-one (3), and tetrazolo[1,5-a]pyrimidin-5-amine (4), were obtained from commercially available reagents and straightforward synthetic methodologies. These new compounds were characterized by infrared (IR), 13C, and 1H NMR spectroscopy, differential scanning calorimetry (DSC), and single-crystal X-ray diffraction. The solvent, temperature, and electron-donating group (EDG) factors that were responsible for the steering of azido-tetrazole equilibrium in all compounds were also studied. In addition, the detonation performance of the target compounds was calculated by using heats of formation (HOFs) and crystal densities. Hirshfeld surface analysis was used to examine the intermolecular interactions of the four synthesized compounds. The results show that the excellent properties of 1-4 are triggered by ionic bonds, hydrogen bonds, and π-π stacking interactions, indicating that these compounds have the potential to be used in the development of high-performance energetic materials. Additionally, DFT analysis is in support of experimental results, which proved the effect of different factors that can influence the azido-tetrazole equilibrium in the synthesized pyrimidine derivatives in the solution.

Cellulose Nitrates-Blended Composites from Bacterial and Plant-Based Celluloses.

Cellulose nitrates (CNs)-blended composites based on celluloses of bacterial origin (bacterial cellulose (BC)) and plant origin (oat-hull cellulose (OHC)) were synthesized in this study for the first time. Novel CNs-blended composites made of bacterial and plant-based celluloses with different BC-to-OHC mass ratios of 70/30, 50/50, and 30/70 were developed and fully characterized, and two methods were employed to nitrate the initial BC and OHC, and the three cellulose blends: the first method involved the use of sulfuric-nitric mixed acids (MAs), while the second method utilized concentrated nitric acid in the presence of methylene chloride (NA + MC). The CNs obtained using these two nitration methods were found to differ between each other, most notably, in viscosity: the samples nitrated with NA + MC had an extremely high viscosity of 927 mPa·s through to the formation of an immobile transparent acetonogel. Irrespective of the nitration method, the CN from BC (CN BC) was found to exhibit a higher nitrogen content than the CN from OHC (CN OHC), 12.20-12.32% vs. 11.58-11.60%, respectively. For the starting BC itself, all the cellulose blends of the starting celluloses and their CNs were detected using the SEM technique to have a reticulate fiber nanostructure. The cellulose samples and their CNs were detected using the IR spectroscopy to have basic functional groups. TGA/DTA analyses of the starting cellulose samples and the CNs therefrom demonstrated that the synthesized CN samples were of high purity and had high specific heats of decomposition at 6.14-7.13 kJ/g, corroborating their energy density. The CN BC is an excellent component with in-demand energetic performance; in particular, it has a higher nitrogen content while having a stable nanostructure. The CN BC was discovered to have a positive impact on the stability, structure, and energetic characteristics of the composites. The presence of CN OHC can make CNs-blended composites cheaper. These new CNs-blended composites made of bacterial and plant celluloses are much-needed in advanced, high-performance energetic materials.

Enhancing Conjugation Effect to Develop Nitrogen-Rich Energetic Materials with Higher Energy and Stability.

This work reports a strategy by enhancing conjugation effect and synthesizes a symmetrical and planar compound, 1,2-bis (4,5-di(1H-tetrazol-5-yl)-2H-1,2,3-triazol-2-yl)diazene (NL24). The incorporation of azo and 1,2,3-triazole moieties manifests a synergistic effect, amplifying the conjugation effect of the azo bridge and thereby elevating the stability of NL24 (Td: 263 °C, IS: 7 J). Notably, NL24, possessing a structural configuration comprising four tetrazoles harboring a total of 24 nitrogen atoms, exhibits excellent detonation performances (ΔHf: 6.06 kJ g-1, VD: 9002 m s-1). This strategy achieves the balance of energy and stability of polycyclic tetrazoles and provides a direction for high-performance energetic materials.

Zero-oxygen balanced fused 1,2,3,4-tetrazine (TNF) as a high-performance energetic material

A straightforward synthesis of 2,9-bis(trinitromethyl)bis([1,2,4]triazolo)[1,5-d:5′,1′-f][1,2,3,4]tetrazine(TNF), achieving an ideal zero oxygen balance in the tetrazine–triazole framework with excellent overall performance.

EM Database v1.0: A benchmark informatics platform for data-driven discovery of energetic materials

Large-scale data demonstrates great significance for the discovery of novel energetic materials (EMs). However, the open-source databases of EMs are not readily available. In pursuit of high-performance EMs before synthetic attempts in the laboratory, the theoretically predicted properties and experimental results that can be easily accessed are desired. Herein, a benchmark informatics platform of EMs, namely EM Database, has been developed for the purpose of data storage and sharing. EM Database v1.0 currently contains the properties of approximately 100000 unique compounds obtained through quantum chemistry (QC) calculations and the experimental results of about 10000 unique compounds extracted from literature. The QC data in the database were extracted via ground-state density functional calculations using the B3LYP/6-31G(d,p) method. These data include geometrical conformation, electronic structures, and predicted properties (i.e., crystal density, enthalpy of sublimation, molar heat of formation, detonation pressure, detonation velocity, detonation heat, and detonation volume) obtained using models of quantitative structure-property relationships. The experimental data were manually collected from literature and were then doubly curated by our project team members. These data include the physicochemical, thermal, combustion, detonation, spectra, and sensitivity properties. In this paper, we also discuss the techniques for constructing the EM Database and present the fundamental features of the database. The EM Database is expected to serve as an effective benchmark informatics platform for forthcoming research on EMs.

Deep Potential Molecular Dynamics Study of Chapman-Jouguet Detonation Events of Energetic Materials.

Detonation of energetic materials (EMs) is of great importance for military applications, while the understanding of detailed events and mechanisms for the detonation process is scarce. In this study, the first deep neural network potential NNP_Shock for molecular dynamics (MD) simulation of shock-induced detonation of EMs was generated based on a deep potential model, providing DFT accuracy but 106 times the computational efficiency. On this basis, we employ our deep potential to perform MD simulations of shock-induced detonation of high-performance EM material 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20, C6H6N12O12) and obtain the theoretical Chapman-Jouguet (C-J) detonation velocities and pressures directly by multiscale shock technique (MSST) for the first time, which are in good agreement with experiment. In addition, the Hugoniot curves and initial reaction mechanisms were successfully obtained. Therefore, the NNP_Shock potential is competent in research of the detonation performance and shock sensitivity of CL-20, and the method can also be transplanted to studies of other EMs.

Hybrid Composites Based on Al/CuO Nanothermites and Tetraamminecopper Perchlorate for High-Performance Energetic Materials

Hybrid Composites Based on Al/CuO Nanothermites and Tetraamminecopper Perchlorate for High-Performance Energetic Materials

Linear furoxan assemblies incorporating nitrobifuroxan scaffold: En route to new high-performance energetic materials

Energetic materials science is undergoing a global renaissance aiming to reach an ideal combination between reliable synthetic strategies, high performance and acceptable molecular stabilities. In this work, design and synthesis of novel energetic non-hydrogen furoxan assemblies has been successfully realized. Fine tunability of molecular composition in a series of furoxan-based materials was achieved by the variation of a number of heterocyclic rings and employing N-oxide regioisomerism strategy. Using this approach, advanced energetic regioisomeric azo-bridged bifuroxan assemblies 6 and 7 as well as 3,4′-dinitro-3′,4-bifuroxan 8 with the excellent overall performance were synthesized. Calculations of Hirshfeld surfaces and molecular electrostatic potentials were conducted to better understand the relationship between the molecular structure and mechanical sensitivity in the synthesized series of energetic materials. It was found, that the supramolecular aggregation of 3,4′-dinitro-3′,4-bifuroxan 8 molecules in crystal is more anisotropic that is commonly believed to be more favorable pattern for the low sensitive substances. All target materials have high densities (1.88–1.95 g cm−3), acceptable thermal stabilities (up to 165 °C), high enthalpies of formation (1.6–2.4 kJ g−1) and positive oxygen balance to CO (up to + 25%). As a result, these compounds exhibit high detonation velocities (9.1–9.5 km s−1), excellent heats of explosion (6.6–7.2 kJ g−1) and combustion performance (Isp = 269–281 s). Therefore, these furoxan-based advanced energetic materials unveil new opportunities in search of next-generation functional organic materials for various applications.

Promising Energetic Melt-Castable Material with Balanced Properties.

As one of the most widely used energetic materials to date, trinitrotoluene (TNT) suffers from several generally known drawbacks such as high toxicity, oil permeability, and poor mechanical properties, which are driving researchers to explore new high-performance energetic melt-castable materials for replacing TNT. However, it still remains a great challenge to discover a promising TNT alternative due to the multidimensional requirements for practical applications. Herein, we reported a new promising energetic melt-castable molecule, 4-methoxy-1-methyl-3,5-dinitro-1H-pyrazole (named as DMDNP). Besides a reasonable melting point (Tm: 94.8 °C), good thermostability (Td: 293.2 °C), and excellent chemical compatibility, DMDNP exhibits some obvious advantages over TNT including more environmentally friendly synthesis, high yield, low toxicity, low volume shrinkage, low mechanical and electrostatic sensitivities, etc., demonstrating well-balanced properties and great promise as a TNT replacement.

Constructing energetic covalent organic frameworks with high stability and low sensitivity

Developing new functional explosives that display high stability, good energy performance, and low sensitivity are one of the key directions of energetic materials research. In this work, two-dimensional (2D) Schiff-based energetic covalent organic frameworks (COFs) are prepared based on triaminoguanidine salts with different anions as building blocks. Benefiting from the robust covalent bond in 2D extended polygons and strong π-π interactions in the eclipsed interlayers, the synthesized energetic COFs showed higher thermal stability and lower mechanical sensitivity than their precursor salts. More importantly, incorporating triaminoguanidine salts into COFs effectively increase the corrosion resistance to metal under high humidity conditions, which is due to the imine moieties in COFs functioning as π acceptors and offering strong bonding with metallic ions. This work provides a new pathway for the development of high-performance energetic materials.

Challenging the Limitations of Tetranitro Biimidazole through Introducing a gem-Dinitromethyl Scaffold

A gem-dinitromethyl group was successfully introduced into the TNBI·2H2O structure (TNBI: 4,4',5,5'-tetranitro-2,2'-bi-1H-imidazole) to obtain 1-(dinitromethyl)-4,4',5,5'-tetranitro-1H,1'H-2,2'-biimidazole (DNM-TNBI). Benefiting from the transformation of an N-H proton into a gem-dinitromethyl group, the current limitations of TNBI were well solved. More importantly, DNM-TNBI has high density (1.92 g·cm-3, 298 K), good oxygen balance (15.3%), and excellent detonation properties (Dv = 9102 m·s-1, P = 37.6 GPa), suggesting that it has great potential as an oxidizer or a high-performance energetic material.

Preparation and Combustion Mechanism of Boron-Based High-Energy Fuels

Due to the characteristics of high energy density and a high calorific value, boron has become a high-energy fuel and shows great potential to be a high-performance candidate for propellants. However, the wide applications of boron are still limited by the characteristics of easy oxidization, ignition difficulty, a long combustion duration, and combustion products that readily adhere to the surface and inhibit full combustion. Therefore, how to overcome the shortcomings and improve the combustion efficiencies of boron-based fuels have become the highlights in exploring novel high-performance energetic materials. In this paper, the prevalent preparation methods and the corresponding combustion mechanisms of boron-based energetic materials are briefly summarized. The results showed that the boron-based energetic materials can be prepared by surface coating, mechanical milling, and ultrasonic mixing methods. At the same time, the corresponding ignition delay and combustion efficiency were also analyzed according to different combustion tests. The results showed that the boron-based composites with different additives had different combustion characteristics. The combustion of boron-based energetic materials can be optimized by removing surface oxide layers, providing extra heat, inhibiting the formation of or the rapid removal of the combustion intermediates, and increasing the diffusion rate of oxygen. With the improvement of the combustion efficiency of boron-based energetic materials, boron-based high-energy fuels will become more and more widely adopted in the future.

An advanced zwitterionic compound based on dinitropyrazole and 1,3,4-oxadiazole: Combining the high detonation performances and low sensitivities

The development of energetic materials with high detonation performances and low sensitivities is a continuous pursuit for researchers. Here, the zwitterionic compound 2 (4-(2-amino-1,3,4-oxadiazol-3-ium-5-yl)-3,5-dinitropyrazol-1-ide) was synthesized, which combined high density with low sensitivity. Compared with its isomer 5-(3,4-dinitro-1H-pyrazol-5-yl)-1,3,4-oxadiazol-2-amine (iso-2), the overall properties of 2 are obviously improved. Significantly, the highly increased crystal density of 2 (2: 1.957 g cm−3 at 193 K; iso-2: 1.719 g cm−3 at 170 K) reveals that zwitterionic compound has a more compact packing model, which positively impacts the detonation properties (2: Dv = 9003 m s−1, P = 36.7 GPa; iso-2: Dv = 8035 m s−1, P = 26.9 GPa). Moreover, the thermostability of 2 (Td = 272 °C) is better than that of iso-2 (Td = 240 °C). Particularly, the mechanical sensitivities of 2 (IS = 40 J, FS = 360 N) are apparently superior to that of traditional high-performance energetic material HMX (IS = 7 J, FS = 120 N), while the detonation performances of 2 still maintain a high level close to HMX (Dv = 9144 m s−1, P = 39.2 GPa). Moreover, the nitroamino compound 3 and azo compound 4 were further developed to improve the detonation properties of 2. Unusually, the detonation properties of 3 (Dv = 8895 m s−1, P = 34.9 GPa) and 4 (Dv = 8887 m s−1, P = 34.8 GPa) were not getting better compared with 2 probably due to their lower densities. Therefore, the advantages of zwitterionic structure can be highlighted. Overall, the synthesis of zwitterionic energetic compounds have broad application prospects in the development of high-performance compounds with low sensitivities.

Synthesis, characterization and properties of halogen-substituted 1,1-diamino-2-nitro-2-(1-amino-1H-tetrazol-5-yl) ethene derivatives as energetic materials

Azo-bridged FOX-7 derivatives with ultra-high theoretical detonation performance were seen as potential high-performance energetic materials. So far, most of the researches were focused on the diverse oxidation reactions involving 1,1-diamino-2,2-dinitroethene (FOX-7) as a starting material, which usually results in undesirable products. In this paper, by replacing the starting substrate from FOX-7 to its analogous 1,1-diamino-2-nitro-2-(1-amino-1H-tetrazol-5-yl) ethene (1), three unexpected halogenated-substituted compounds (2-4) were obtained rather than the anticipated azo-bridged products. The crystal structures of 2-4 were fully determined by single-crystal X-ray diffraction. The reaction mechanism and physicochemical properties to them were deeply investigated. 4 shows good detonation performance (Dv = 7554 m/s, P = 24.3 GPa), which are superior to these of TNT (Dv = 6881 m/s, P = 19.5 GPa). The methodology may be helpful for the exploration of azo-bridged FOX-7 compounds in the future.

High-strength and energetic Al2Ti6Zr2Nb3Ta3 high entropy alloy containing a cuboidal BCC/B2 coherent microstructure

The present work developed a novel high-strength and energetic Al 2 Ti 6 Zr 2 Nb 3 Ta 3 high entropy alloy (HEA) containing a BCC/B2 coherent microstructure. The microstructural evolution of BCC/B2 with both the aging temperature (873 ~ 1073 K) and aging time (up to 200 h) was investigated, from which it was found that the cuboidal BCC nanoparticles are coherently-precipitated into the B2 matrix in 873 K-aged state due to a moderate lattice misfit ( ε ~ - 0.76%). The increase of aging temperature could destroy the BCC/B2 coherency and accelerate the formation of brittle Zr 5 Al 3 phase. Especially, the BCC/B2 microstructure exhibits an excellent thermal stability, as evidenced by the fact that these cuboidal BCC nanoprecipitates were not coarsened obviously at 873 K with the particle size from r ~ 10 nm in 24 h-aged state to r ~ 20 nm in 200 h-aged state. This alloy possesses prominent mechanical properties with high yield strength at both room temperature ( σ YS = 1193 MPa) and elevated temperatures (1060 MPa at 873 K and 106 MPa at 1273 K), where the high strength was discussed in light of the precipitation strengthening mechanism. Importantly, the current alloy has an ultrahigh combustion calorific capacity with a value of 10240 J·g -1 , showing a great potential to be used as novel high-performance energetic structural materials. • A high-strength and energetic HEA was developed with the cluster formula approach. • High-strength of alloy was realized by forming a BCC/B2 coherent microstructure. • The BCC/B2 coherent microstructure exhibits a higher thermal stability at 873 K. • The alloy has an ultrahigh combustion calorific value of 10240 J·g -1 .

Imparting high polymorph transition resistance to cyclotetramethylene-tetranitramine via spherulitic aggregation enabled crystal shape constraint

The high melting explosive (HMX), i.e., cyclotetramethylene-tetranitramine, is plagued by issues such as structural instability, increased sensitivity, and unwanted deflagration at elevated temperatures, which are strongly linked to the microstructural damage generated by its β → δ polymorphic transition around 160–185 °C. An extension of the β form thermal stability is therefore desired. Herein, a new strategy to regulate such β → δ transition via particle-level aggregation is demonstrated. Using polyvinyl pyrrolidone as a growth additive, this study shows that single-crystalline β-HMX can evolve into a unique spherulitic morphology with fine control over particle sizes and compactness. The phase transition is then found sensitive to the spherulitic aggregation while highly correlating with the decrease in particle size. Remarkably, the β-HMX spherulites exhibit an onset transition temperature of up to 205 °C, corresponding to a maximum 20 °C increment as compared with the highest value achieved by its single crystalline counterpart. Mechanistic investigation reveals that the suppressed β → δ transition origins from the restricting of anisotropic expansion of the subunit crystallites in spherulitic aggregates, induced by their unusual radial packing mode. The proposed strategy is expected to be translated to other polymorphic explosives, hence bringing a fresh perspective to future high-performance energetic materials development.

Searching for high performance asymmetrically substituted teterazine energetic materials based on 3-hydrazino-6-(1H-1,2,3,4-tetrazol-5-ylimino)-s-tetrazine

Tetrazine compounds are promising candidates of high performance energetic materials (EMs). For the purpose of exploring high performance asymmetrically substituted teterazine explosives, 3-hydrazino-6-(1H-1,2,3,4-tetrazol-5-ylimino)-s-tetrazine was selected as the precursor and a series of teterazine EMs were prepared based on three synthetic strategies. All the obtained compounds were fully characterized and the crystal structures of seven compounds were further confirmed by single crystal X-ray diffraction. The thermal dynamics and thermal safety parameters, the detonation properties and impact sensitivities were also obtained. The results revealed that compounds 15–17 show excellent energetic properties (detonation velocities > 9000 m·s−1, detonation pressures > 30 GPa) and have impact sensitivities (8–12 J) that comparable or lower than RDX. Compounds 9–13 are insensitive to impact and have detonation velocities range from 8452 to 8775 m·s−1. These compounds can be good candidates of high performance secondary explosives or insensitive EMs.

Predicting impact sensitivity of energetic materials: insights from energy transfer of carriers

The impact sensitivity to external stimuli is a critical parameter to evaluate and design high-performance energetic materials (EMs). Investigating factors that affect sensitivity and further revealing the sensitivity mechanism are still huge challenges. In the present study, a physical model is established to assess impact sensitivity of 16 energetic compounds based on the energy transfer of carriers using first-principles calculation. The results show that the empirical parameter ψ obtained by considering the band gap, the density of states, and the ability of electronic migration has a remarkable correlation with experimental drop energy E50. This is in favor of the basic assumption that the energetic material would be less sensitive if the electrons transfer energies quickly to other molecules, making it harder to form a hot spot.