Advanced Energetic Materials Research Articles

Multi-Level Structural Design Strategy toward Low-Sensitivity Energetic Materials: From Planar Molecule to Layered Packing Crystal

Layered packing structures have been of great interest in the field of energetic materials (EMs) due to their excellent balances between energy and safety. Nevertheless, the present advanced layered EMs and rational design approaches are still lacking. In this work, we proposed a multi-level structural design strategy for layered EMs, from molecular to crystal level. Inspired by the experimentally known energetic crystals with the specific NH2···NO2 intermolecular motifs, we established a set of guidelines for designing and screening potential target molecules based on the H2N–C–C–NO2 moiety via a systematic analysis of structure/composition–performance relationships. Subsequently, the possible crystal packing structures were searched accurately by the evolutionary algorithm USPEX coupled with a recently developed energetic molecule-specific polarizable force field. The theoretical results show that B1 (4,4′-diamino-3,3′-dinitro-[5,5′-biisoxazole] 2,2′-dioxide) and C2 [(E)-3,3′-(diazene-1,2-diyl) bis (4-amino-5-nitroisoxazole 2-oxide)] are promising candidates of advanced layered EMs with good mechanical sensitivities (better than TNT) and detonation performances (superior to FOX-7). Hopefully, our multi-level design procedure can accelerate the discovery of novel layered EMs with advanced properties.

Regioselective Introducing N-Oxide Groups Onto 6-Trifluoromethyl-1,2,4,5- Tetrazine-3-Amine for Obtaining Advanced Energetic Materials

Regioselective Introducing N-Oxide Groups Onto 6-Trifluoromethyl-1,2,4,5- Tetrazine-3-Amine for Obtaining Advanced Energetic Materials

Rheological kinetics of ferrocenylsilane functionalized polyurethanes based on 4,4'‐methylenediphenyl diisocyanate for advanced energetic materials

Abstract4,4′‐Methylenediphenyl diisocyanate (4,4'‐MDI) is a symmetric aromatic isocyanate commonly used as a curing agent in the production of polyurethanes (PUs). The chemorheology and kinetics of its reaction with a metallocenic‐prepolymer derivative from hydroxyl‐terminated polybutadiene (HTPB) is studied in bulk and under isothermal conditions at 50–80°C by means of rheological measurements. The viscosity of the initial part of the PU formation, the pregel stage governed by viscous behavior, is modeled through the Arrhenius rheokinetic model. This thermoplastic elastomer undergoes gelation, a transition that is analyzed in depth together with predictions according to percolation theory. The gel point (tgel) is determined from the intersection in tan δ versus curing time for different shear frequencies. From the viscoelastic properties, like the elastic storage modulus (G'), the conversion degree is determined, and the entire polymerization process is modeled through the Kamal‐Sourour and Sato kinetic expressions. Significant variation in the reaction orders and the activation energies might reveal a change in the process mechanism, depending on the temperature. This work demonstrates that an indirect method makes it possible to gain relevant knowledge about the chemistry of these thermoplastic PUs during curing, which is essential for their manufacturing. This study merits attention for the development of a new generation of high‐performance binders with great potential in aerospace propulsion.

Nitroxy- and azidomethyl azofurazans as advanced energetic materials

Progress in the rocket industry is only possible on the basis of new, higher performance and more environmentally friendly materials compared to up-to-date propellant ingredients for liquid, solid, gelled and hybrid propellant systems. In this work, synthetic methods have been developed for the preparation of new energetic azofurazans bearing nitroxymethyl or azidomethyl groups. All prepared compounds were fully characterized by multinuclear NMR and IR spectroscopies, as well as elemental analyses. An analysis of the structural features based on the X-ray single-crystal diffraction made it possible to discuss their influence on the densities of the azofurazans of this study. Thermal decomposition and combustion of nitroxymethyl and azidomethyl azofurazans were studied using a number of complementary experimental techniques, namely thermogravimetry, differential scanning calorimetry, manometry, microthermocouple measurements in the combustion wave. The structural and physical characteristics of these new energetic analogues illustrate the extent to which the nature of the explosophoric groups can be used to tune the performace of the azofurazan framework. These azofurazans possess positive calculated enthalpy of formation and are promising candidates for new environmentally friendly energetic materials.

Intramolecular integration of multiple heterocyclic skeletons for energetic materials with enhanced energy & safety

The research for new generations of high explosives with the remarkable overall performance has always been a challenging task. Currently, the research priority of energetic materials is to explore new design strategies to balance and/or break the energy-safety limits. In this study, an intramolecular integration of various heterocyclic skeletons based on the unique superiority of each heterocycle was developed. By employing this approach, an advanced energetic molecule integrating 1,2,5-oxadiazole, 1,2,4-oxadiaozle and pyrazole skeletons, 5-(3,4-dinitro-1H-pyrazol-5-yl)-3-(4-nitro-1,2,5-oxadiazol-3-yl)-1,2,4-oxadiazole (6), was designed and prepared. The energy level (e.g., detonation velocity: 9094 m s−1) of 6 is approaching that of the extensively used high explosive, RDX (8801 m s−1), while its safety (impact sensitivity: IS = 24 J; thermal stability: Tdec = 265 °C) are obviously superior to that of RDX (IS = 7.4 J; Tdec = 204 °C). These favorable energetic properties demonstrate the outstanding overall performance of 6. Moreover, the variation of sensitivities and thermal stabilities were further investigated through the quantum chemistry methods based on the single-crystal data. Our study is anticipated to attract more in-depth study on the promising intramolecular integration approach and accelerate the development of the advanced energetic materials.

Functionalized Tetrazole Energetics: A Route to Enhanced Performance

AbstractTetrazoles are a class of heterocyclic compounds. Many tetrazole derivatives have been studied extensively as potential high energy materials. Compared with other nitrogen‐rich heterocycles, most tetrazole‐based heterocycles demonstrate superior properties due to the higher density and heat of formation levels. A large variety of advanced energetic materials have been achieved based on the combination of tetrazole moieties with a collection of bridges. This review is an overview of the recent developments of energetic tetrazole structures, and where possible, information such as the synthetic methods, and physical and detonation properties are provided. Given the synthetic opportunities and outstanding properties, energetic materials based on tetrazole structures are undoubtedly promising candidates for the development of highly energetic materials for civilian or military applications.

Review on Advanced Energetic Materials for Insensitive Munition Formulations

Insensitive munitions are munitions that are chemically stable enough to withstand thermal, mechanical, or electrical stimuli during storage and transportation, and can still explode as intended to defeat their targets. Extensive programmes have evolved worldwide for the development and introduction of insensitive munitions (IMs). The use of insensitive energetic materials significantly improves the protection of modern nuclear warheads and increases the survivability of conventional munitions in hustle environment. The most basic level to obtain insensitive munitions is the use of intrinsic insensitive energetic materials, either by synthesizing new, less sensitive crystalline materials or by improving the physical properties of existing sensitive materials. In light of the growing importance of insensitive munitions, this review paper brings out some potential insensitive energetic materials and plasticizers emphasizing their significant role in the development of futuristic IM formulations. This review also concisely brings out the recent work carried out globally, including India, on the development of advanced energetic materials and their insensitive energetic formulations.

Construction of an Unusual Two-Dimensional Layered Structure for Fused-Ring Energetic Materials with High Energy and Good Stability

Abstract The creation of high-performance energetic materials with good mechanical sensitivities has been a great challenge over the past decades, since such materials have huge amounts of energy and are thus essentially unstable. Here, we report on a promising fused-ring energetic material with an unusual two-dimensional (2D) structure, 4-nitro-7-azido-pyrazol-[3,4-d]-1,2,3-triazine-2-oxide (NAPTO), whose unique 2D structure has been confirmed by single-crystal X-ray diffraction. Experimental studies show that this novel energetic compound has remarkably high energy (detonation velocity D = 9.12 km·s−1; detonation pressure P = 35.1 GPa), excellent sensitivities toward external stimuli (impact sensitivity IS = 18 J; friction sensitivity FS = 325 N; electrostatic discharge sensitivity EDS = 0.32 J) and a high thermal decomposition temperature (203.2 °C), thus possessing the dual advantages of high energy and low mechanical sensitivities. To our knowledge, NAPTO is the first fused-ring energetic material with 2D layered crystal stacking. The stabilization mechanism toward external stimuli were investigated using molecular simulations, and the theoretical calculation results demonstrate that the ultraflat 2D layered structure can buffer external mechanical stimuli more effectively than other structures by converting the mechanical energy acting on the material into layer sliding and compression. Our study reveals the great promise of the fused-ring 2D layered structure for creating advanced energetic materials.

Melamine N-oxide based self-assembled energetic materials with balanced energy & sensitivity and enhanced combustion behavior

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.

Energetic azide-based coordination polymers: Sensitivity tuning through diverse structural motifs

Energetic coordination polymers (ECPs), as a new class of energetic materials (EMs), have attracted extensive attention in recent years. However, controllable modulation of mechanical sensitivities and the establishment of structure-function theoretical models of ECPs to meet different applications remain great challenges. Herein, we designed and synthesized four azide-based ECPs, [Cd2(N3)2(datz)2]n1 (Hdatz = 3,5-diamino-1,2,4-triazole), [Cd(N3)2(brt)2]n2 (brt = 4,4′-bi-1,2,4-triazole), [Cd(N3)2(btzp)]n3 (btzp = 1,3-di(tetrazol-1-yl)propane), and [Cd2(N3)4(btzb)]n4 (btzb = 1,4-bis(tetrazol-1-yl)butane). Because of the existence of consolidated network structures, high-energy linkers, and diverse structural motifs, compounds 1–4 exhibit reliable thermal stabilities, tunable mechanical sensitivities, and considerable heats of detonation (ΔHdet) with the ΔHdet values of 3.390, 3.412, 3.947 and 4.504 kJ·g−1, respectively, which are two times higher than those of commercial LA (lead azide) and the reported AgMtta (AgMtta = [Ag(Mtta)]n, HMtta = 5-methyl-1H-tetrazole). The sensitivity measurements demonstrate that the sensitivity toward impact of 1–4 displays in the following order: 1 (>40 J) ≪ 2 (8 J) < 3 (2.5 J) < 4 (2 J). In particular, compound 1 features scarce insensitivity compared with sensitive 2, 3, 4 and most of known azide-based EMs. Furthermore, theoretical calculations, structural analyses, and experimental results revealed that the different sensitivities of the four ECPs are mainly dependent on two different structure models for the first time. The insensitive 1 is “body frame structure” model, while the sensitive 2–4 belong to “non-body frame structure” model. Our study enlightens new insights into structures behind mechanical sensitivities for optimizing advanced EMs.

Energetic materials based on poly furazan and furoxan structures

Furazan and furoxan represent fascinating explosophoric units with intriguing structures and unique properties. Compared with other nitrogen-rich heterocycles, most poly furazan and furoxan-based heterocycles demonstrate superior energetic performances due to the higher enthalpy of formation and density levels. A large variety of advanced energetic materials have been achieved based on the combination of furazan and furoxan moieties with different kinds of linkers and this review provides an overview of the development of energetic poly furazan and furoxan structures during the past decades, with their physical properties and detonation characteristics summarized and compared with traditional energetic materials. Various synthetic strategies towards these compact energetic structures are highlighted by covering the most important cyclization methods for construction of the hetercyclic scaffolds and the following modifications such as nitrations and oxidations. Given the synthetic availabilities and outstanding properties, energetic materials based on poly furazan and furoxan structures are undoubtedly listed as a promising candidate for the development of new-generation explosives, propellants and pyrotechnics.

Review on Advanced Energetic Materials for Insensitive Munition Formulations

Review on Advanced Energetic Materials for Insensitive Munition Formulations

Insight into the roles of small molecules in CL-20 based host–guest crystals: a comparative DFT-D study

The host–guest inclusion strategy has emerged as a promising method for developing advanced energetic materials and has been successfully applied to a CL-20 crystal.

Synthesis, Characterization and Performance of Promising Energetic Materials Based on 1,3-Oxazinane.

1,3-oxazinane is an ideal framework for advanced energetic materials because of its compact skeleton and the presence of several modifiable sites. However, investigations on characterization and performance of 1,3-oxazinane energetic compounds are extremely limited. Two heterocyclic 1,3-oxazinane molecules were synthesized under different Mannich condensation processes and further reacted to form nitro- and azide-substituted energetic compounds 3,5,5-trinitro-1,3-oxazinane (TNTON) and 5-azido-3,5-dinitro-1,3-oxazinane (ADTON), in good yields. Interestingly, the two energetic molecules showed distinct physical properties. ADTON shows an impressive glass transition temperature (Tg) as low as -46 °C with high density, which is highly suitable for rate-accelerating materials. TNTON exhibits good thermal stabilities (melting point of 89 °C and a decomposition point of 231 °C) and highly insensitive behavior (38 J, 360 N). The theoretical detonation pressure of TNTON is ca. 63 % higher than that of TNT, indicating broad application prospects in melt-cast explosives.

New Strategy for Enhancing Energetic Properties by Regulating Trifuroxan Configuration: 3,4-Bis(3-nitrofuroxan-4-yl)furoxan

It is of current development to construct high–performance energetic compounds by aggregation of energetic groups with dense arrangement. In this study, a hydrogen-free high-density energetic 3,4-bis(3-nitrofuroxan-4-yl)furoxan (BNTFO-I) was designed and synthesized in a simple, and straightforward manner. Its isomer, 3,4-bis(4-nitrofuroxan-3-yl)furoxan (BNTFO-IV), was also obtained by isomerization. The structures of BNTFO-I and BNTFO-IV were confirmed by single-crystal X-ray analysis for the first time. Surprisingly, BNTFO-I has a remarkable calculated crystal density of 1983 g cm−3 at 296 K, which is distinctly higher than BNTFO-IV (1.936 g cm−3, 296 K), and ranks highest among azole-based CNO compounds yet reported. It is noteworthy that BNTFO-I exhibits excellent calculated detonation properties (vD, 9867 m s−1, P, 45.0 GPa). The interesting configuration differences of BNTFO-I and BNTFO-IV provide insight into the design of new advanced energetic materials.

Structure–Property Relationship in Energetic Cationic Metal–Organic Frameworks: New Insight for Design of Advanced Energetic Materials

Understanding the structure–property relationship in a material is of great importance in materials science. To study the effect of ligand backbones and anionic groups on the properties of energeti...

Highly scalable discrete-particle simulations with novel coarse-graining: accessing the microscale

ABSTRACTSimulating energetic materials with complex microstructure is a grand challenge, where until recently, an inherent gap in computational capabilities had existed in modelling grain-scale effects at the microscale. We have enabled a critical capability in modelling the multiscale nature of the energy release and propagation mechanisms in advanced energetic materials by implementing, in the widely used LAMMPS molecular dynamics (MD) package, several novel coarse-graining techniques that also treat chemical reactivity. Our innovative algorithmic developments rooted within the dissipative particle dynamics framework, along with performance optimisations and application of acceleration technologies, have enabled extensions in both the length and time scales far beyond those ever realised by atomistic reactive MD simulations. In this paper, we demonstrate these advances by modelling a shockwave propagating through a microstructured material and comparing performance with the state-of-the-art in atomistic reactive MD techniques. As a result of this work, unparalleled explorations in energetic materials research are now possible.

Pushing the Limits of Oxygen Balance in 1,3,4-Oxadiazoles.

Gem-trinitromethyl groups were introduced into a 1,3,4-oxadiazole ring to give the first example of a bifunctionalized single five-membered ring with six nitro groups. 2,5-Bis(trinitromethyl)-1,3,4-oxadiazole (12) has a high calculated crystal density of 2.007 g cm-3 at 150 K (1.941 g cm-3 at 293 K) and a very high positive oxygen balance (39.12%), which makes it a strong candidate as a high energy dense oxidizer. The dihydroxylammonium and dihydrazinium salts of bis(trinitromethyl)-1,3,4-oxadiazole (5 and 6) exhibit excellent calculated detonation properties (5, vD = 9266 m s-1, P = 38.9 GPa; 6, vD = 8900 m s-1, P = 36.3 GPa) and acceptable impact sensitivities (5 20 J, 6 19 J), which are superior to those of RDX (7.4 J) and HMX (7.4 J). Such attractive features support the application potential of the gem-polynitromethyl group in the design of advanced energetic materials. Surprisingly, 2,5-bis(trinitromethyl)-1,3,4-oxadiazole (12) is more thermally stable and less sensitive than its bis(dinitromethyl) analogue, 8.

The Impacting Dynamic Response of Energetic Materials PTFE/Al

PTFE/Al is the most representative of a new class of advanced energetic materials. In order to study the dynamics response under impact, carrying out numerical simulation for the pressure changes and plastic deformation which were generated from PTFE/Al with a metal shell penetrating aluminum alloy target by using LSDYNA. By analyzing the pressure on the observation point, flash and unit deformation characteristic, summarizing Energetic Materials PTFE/Al impact dynamic response. Combining the literature experimental results verify that the simulation is reasonable.

Comparative Study of Various Pyrazole-based Anions: A Promising Family of Ionic Derivatives as Insensitive Energetic Materials.

In the design of advanced energetic materials, high-density explosophores play a pivotal role because of their remarkable enhancement of both density and molecular stability. Using diversified functionalization strategies, a comparative study involving various nitropyrazole anions shows that these are crucially important in determining performance and stability. A promising family of pyrazole-based energetic ionic derivatives were synthesized and characterized by NMR and IR spectroscopies, and elemental analysis. Among them, 7, 8, 11-13 exhibit favorable overall performance as energetic materials.