Traditional Energetic Materials Research Articles

Insensitive energetic azide-based metal-organic frameworks: Highly stable frameworks constructed by nitrogen-rich and rigid ligands

The design and development of azide-based energetic metal–organic frameworks (EMOFs) with high energy and reliable stabilities for energetic materials still remains significant challenges. Herein, we utilized two rigid triazole-based polydentate ligands to design and synthesize two stable azide-based EMOFs [Cd(N3)(TRZ)]n1 (HTRZ = 1,2,4-triazole) and [Cd(N3)(ATRT)(H2O)]n2 (HATRT = 5-amino-3-(4H-1,2,4-triazol-4-yl)-1H-1,2,4-triazole). Structural analysis reveals that 1 displays a unique 3D inserted 3D framework, and 2 presents a rigid 2D network with strong π-π packing interactions. Compounds 1 and 2 feature rarely insensitive to mechanical stimulation and exhibit excellent thermal stabilities reaching up to 371 and 366 °C, respectively. The calculated heats of detonation (ΔHdet) of 2 is 5.315 kJ·g−1, which is much higher than that of the traditional explosive 2,4,6-trinitrotoluene (TNT, ΔHdet = 3.72 kJ·g−1). The experimental results and theoretical calculations demonstrate that the specific 3D inserted 3D structure of 1 and the rigid 2D network of 2 produce high mechanical strength. This study not only provides two azide-based EMOFs with reliable stabilities as potential replacements for traditional energetic materials, but also illustrates a new insight into building stable structural models of azide-based EMOFs.

Searching new cocrystal structures of CL-20 and HMX via evolutionary algorithm and machine learning potential

In this work, we report the discovery of energy cocrystals using an efficient iterative workflow combining an evolutionary algorithm and a machine learning potential (MLP). The compound 2,4,6,8,10,12-Hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) has attracted significant attention owing to its higher energy density than traditional energetic materials. However, the higher sensitivity has limited its applications. An important way to reduce its sensitivity involves cocrystal engineering with traditional explosives. Many cocrystal structures are expected to be composed of these two components. We developed an efficient iterative workflow to explore the phase space of CL-20 and 1,3,5,7-tetranitro-1,3,5,7-tetraazacyclooctane (HMX) cocrystals using an evolutionary algorithm and an MLP. The algorithm was based on the Universal Structure Predictor: Evolutionary Xtallography (USPEX) software, and the MLP was the reactive force field with neural networks (ReaxFF-nn ) model. A set of high-density cocrystal structures was produced through this workflow; these structures were further checked via first-principles geometry optimizations. After careful screening, we identified several high-density cocrystal structures with densities of up to 1.937 g/cm3 and HMX: CL-20 ratios of 1:1 and 1:2. The influence of hydrogen bonds on the formation of high-density cocrystals was also discussed, and a roughly linear relationship was found between energy and density.

Theoretical study of a series of 1,2-diazete based trinitromethyl derivatives as potential energetic compounds.

Explosive properties of novel potential high energy density materials of a series of 1,2-diazete-based molecules with trinitromethyl functional group were investigated computationally. All the sixty seven molecules were optimised to obtain their molecular geometries and electronic structures. Electrostatic potential analysis was also carried out in the determination of different parameters. The calculations indicate that the majority of the compounds have high positive heat of formations, high density and good detonation performance greater than that of traditional energetic materials like RDX and HMX. They are also having comparable values of impact sensitivity. These features promise their potential to be used as energetic materials for future applications. Most of the designed molecules are having high positive oxygen balance values so that the study of these molecules can also be extended as potential candidates for oxidisers in solid propellants. Optimisation and vibrational frequency analysis of the studied molecules were done with density functional theory using B3LYP/aug-cc-pVDZ as the basis set to zero imaginary frequencies using Gaussian 09. Electrostatic potential analysis were carried using the Multiwfn program.

Structural and decomposition analysis of TKX-50 with vacancy defects: insights from DFT and AIMD simulations.

Vacancy defects are commonly present in crystals of energetic materials, and significantly influence the structural stability and decomposition mechanisms. However, there is a lack of profound understanding regarding the introduction of vacancy defects in energetic ionic salt, dihydroxylammonium 5,5'-bitetrazole-1,1'-dioxide (TKX-50). Due to the 1 : 2 ratio of anions to cations, TKX-50 possesses a more complex distribution of vacancy defects compared to traditional energetic materials. Based on the density functional theory method, the relatively favorable thermodynamic formation of vacancy defect distributions was revealed. The noncovalent interactions within the system, as well as the planarity of the anions, were investigated to understand the structural stability of TKX-50. Through ab initio molecular dynamics simulations, we discovered that vacancy defects can expedite the proton transfer during the initial decomposition stage of TKX-50 and affect the pathways of proton transfer. In the subsequent decomposition process, introduction of vacancy defects in the TKX-50 crystal leads to an earlier onset of ring-opening reactions and accelerates the appearance of decomposition products. The findings have the potential to provide insights into modeling vacancy defects in energetic ionic salts and reveal the impact of such defects on the structural stability and decomposition mechanisms of these materials.

Persistence of 2,4,6-triamino-1,3,5-trinitrobenzene in the environment

2,4,6-triamino-1,3,5-trinitrobenzene (TATB) is an Insensitive High Explosive (IHE) that is increasingly being used as a safer alternative to traditional energetic materials. However, the high thermal stability of TATB poses challenges for its disposal, particularly through existing open burning methods and its ability to remain in the environment for long period of time. Therefore, this study investigated the persistence of TATB in the environment by conducting small-scale experiments which were designed to examine the resistance of TATB to open burning and to assess unburnt residues. To evaluate the fate and transport of the unburnt materials in soil, laboratory-scale soil column transport studies were conducted to gauge the movement of TATB through soil. The results indicate that TATB exhibits a high resistance to burning, leaving unburnt materials that can persist in soil. The study emphasizes the importance of efficient disposal methods for explosives and highlights the need for further research to understand the environmental impact and toxicity of TATB.

Emulsion Explosives: A Tutorial Review and Highlight of Recent Progress.

Emulsion explosives (EE) have been commercially available in various forms for over 50 years. Over this period, the popularity and production technology of this class of energetic materials have been developing constantly. Despite this rapid rise to prominence and, in some applications, prevalence over traditional energetic materials, remarkably little information is available on the physicochemical and energetic properties of these materials and factors affecting those properties. This work is dedicated to presenting the fundamental information relevant to the features, properties and applications of EEs, while highlighting the most significant recent progress pertaining to those materials. Particular emphasis has been given to providing information about the types, composition, modifications and detonation parameters of EEs, as well as to highlighting the less obvious, emerging applications of EEs.

Synthesis, characterization and properties of amphoteric heat-resistant explosive materials: Fused [1,2,5]oxadiazolo [3′,4′:5,6]pyrido[4,3-d][1,2,3]triazines

• The tricyclic triazine oxide was synthesized as the first fused amphoteric energetic molecule. • These compounds exhibited high decomposition temperatures (310–344 °C). • All the non-metallic compounds have better detonation properties than HNS and PYX and low sensitivities. • The perchlorate salt is a potential candidate for heat-resistant explosive. Fused cyclic energetic compounds are a unique class of large conjugated structures containing two or more rings, and have been identified as promising competitors for traditional energetic materials. In the present work, we investigated 5-amino-6-oxo-4,6-dihydro-[1,2,5]oxadiazolo[3′,4′:5,6]pyrido[4,3- d ][1,2,3]triazine 8-oxide ( 3 ) in detail as a fused amphoteric energetic molecule that can be protonated and deprotonated by acids and bases to obtain its cationic ( 11 – 13 ) and anionic ( 4 – 10 ) salts. All the new compounds were thoroughly characterized by infrared and multinuclear NMR ( 1 H and 13 C) spectroscopy, and elemental analysis. The structural features of 3 – 6 , 9 , 10 , 12 , and 13 were investigated by single-crystal X-ray diffractions and different theoretical techniques (Hirshfeld surfaces analyses, and noncovalent interactions). The aromaticity of compound 3 was studied via localized orbital locator- π and iso -chemical shielding surfaces (ICSS). Their thermal decomposition temperatures were investigated by differential scanning calorimetry and thermogravimetry to be 310–344 °C (onset). In addition, impact and friction tests revealed that these compounds were insensitive. Densities, heats of formation and detonation properties were measured by a gas pycnometer, calculated using the Born-Haber energy cycle and EXPLO5 v6.05.04 program, respectively. The neutral compound 3 and all its non-metallic salts have better detonation properties than HNS and PYX and lower sensitivities. In particular, salt 11 (N + O: 61.74 %, T d : 330 °C, Δ H f : 1.68 kJ g −1 , D : 8.795 km s −1 , P : 36.0 GPa, IS: > 40 J, FS: > 360 N) is a potential candidate for heat-resistant explosives.

Theoretical research on cage-like furazan-based energetic compounds and its derivatives.

In this manuscript, we reported the design and prediction of two furazan-based cage-like molecules and their derivatives using density function theory (DFT). The heat formation and detonation properties were calculated using Hess's law and Kamlet-Jacobs equations with the B3PW91 method. The molecular stability and geometry were analyzed using the M06-2X method, and molecular crystal structures were predicted based on Monte Carlo simulation, while chemical reactive sites were judged using the PBE0 method based on Fukui function. The theoretical calculation result proved that the designed molecules exhibit ideal symmetric cage-like geometry and show superior physicochemical and detonation properties. Compared with traditional energetic materials, the designed molecules display more positive solid heat formation and lower sensitivity. The designed molecules could be considered promising high energy density material candidates with potential synthesis and application value. Two designed molecules display superior detonation performance and ideal completely symmetric cage-like geometry, which were proved theoretically as a promising HEDM candidate. A series of derivatives also exhibited excellent crystal density and physicochemical properties, while with more stable structure.

Clustering rooting for the high heat resistance of some CHNO energetic materials

Highly thermostable energetic materials (EMs) are highly desired for deep underground and space exploration, and therefore have attracted much attention. This work employs four typical traditional EMs composed of C, H, N and O atoms as example to clarify the origin of high heat resistance, by means of molecular dynamics simulations with the molecular reactive forcefield of ReaxFF. These EMs include 3,5-dinitro-N,N´-bis(2,4,6-trinitrophenyl)pyridine-2,6-diamine (PYX), 1,3,5-diamino-2,4,6-trinitrobenzene (TATB) and 2,2´,4,4´,6,6´-hexanitrostilbene (HNS), which are highly thermostable with decomposition temperature peaks > 600 K, and a less one of pentaerythritol tetranitrate (PETN) for comparison. It is found that the clustering in the decomposition of PYX, TATB and HNS retards the extraction of small product molecules from clusters, as well as heat release, and thereby roots for their high heat resistance; while, the clustering in the PETN decay is negligible and heat release and fragmentation proceed rapidly, facilitating to fast decomposition. Combining this finding with the well-known molecular stability, this work presents a perspective on the high heat resistance of traditional EMs. Based on it, a highly negative oxygen balance, a high C content and a high molecular stability are proposed as a strategy for designing and constructing new highly heat-resistant EMs.

Theoretical studies on oxadiazole-based layer stacking nitrogen-rich high-performance insensitive energetic materials.

A series of energetic compounds derived from substituted oxadiazole molecules which were theoretically proved to have π-π stacking crystal structure using NIC method and QTAIM theory were designed and investigated theoretically as novel high-performance insensitive energetic materials. The heats of formation (HOFs) and detonation parameters were predicted based on Kamlet-Jacobs equations and Born-Haber cycle. All energetic compounds and derivatives were calculated at DFT-B3PW91/6-31G++(d,p) level and exhibited ideal oxygen balance (OB%) (- 19.50~15.68), positive heats of formation (424.0~957.4kJ/mol), and pleasant crystal density (1.707~1.901g/cm3). The predicted results revealed that detonation performances of some designed molecules are equal to traditional energetic materials while they are more stable and insensitive that can be considered to have potential synthesis and application value. Graphical abstract BRIEFS Three energetic molecules that proved may have a π-π stacking crystal structure and its derivatives were designed and investigated theoretical as novel high-performance insensitive energetic materials. The most of compounds exhibited positive solid phase heat of formation, idea oxygen balance and structural stability.

The Summary of Synthesis and Theoretical Research into Cocrystal Explosives

With the complexity of the using environment, traditional energetic materials can no longer meet the requirements, and it is urgent to synthesize new energetic materials. As a new type of explosive modification technology, cocrystallization is utilized widely in the field of energetic materials. The researchers mainly employ solvent method to synthesize different kinds of cocrystal explosives and utilise molecular dynamics simulation method to study the properties of different cocrystal explosives. In this paper, the theoretical research and experimental preparation of cocrystal explosives are summarized, and the application of cocrystal technology in energetic materials is analyzed. Both theoretically and experimentally, the results show that cocrystallization can improve the properties of explosives and provide a new and effective way for the modification of explosives.

Constructing Strategies and Applications of Nitrogen-Rich Energetic Metal–Organic Framework Materials

The synthesis of energetic metal–organic frameworks (EMOFs) with one-dimensional, two-dimensional and three-dimensional structures is an effective strategy for developing new-generation high-energy-density and insensitive materials. The basic properties, models, synthetic strategies and applications of EMOF materials with nitrogen-rich energetic groups as ligands are reviewed. In contrast with traditional energetic materials, EMOFs exhibit some interesting characteristics, like tunable structure, diverse pores, high-density, high-detonation heat and so on. The traditional strategies to design EMOF materials with ideal properties are just to change the types and the size of energetic ligands and to select different metal ions. Recently, some new design concepts have come forth to produce more EMOFs materials with excellent properties, by modifying the energetic groups on the ligands and introducing highly energetic anion into skeleton, encapsulating metastable anions, introducing templates and so on. The paper points out that appropriate constructing strategy should be adopted according to the inherent characteristics of different EMOFs, by combining with functional requirements and considering the difficulties and the cost of production. To promote the development and application of EMOF materials, the more accurate and comprehensive synthesis, systematic performance measurement methods, theoretical calculation and structure simulation should be reinforced.

Theoretical investigation of nitrogen-rich high-energy-density materials based on furazan substituted s-triazine.

A series of furazan substituted s-triazine derivatives were designed and investigated theoretically as potential nitrogen-rich high-energy-density materials in this work. Density functional theory (DFT) methods were used to predict the heats of formation (HOFs) and compounds structure was optimized at B3PW91/6-31G++ (d,p) level. The explosive detonation parameters were calculated based on Kamlet-Jacobs equations and Born-Haber cycle. The presence of the -NO2 and - NH2 groups in the same structure were found to be helpful in improving structural stability through intramolecular weak interactions. Most of the designed compounds were characterized by high HOFs (solid-phase heat of information 71.01-518.20kJ/mol) and crystal density values (1.74-1.90g/cm3). In the analysis of frontier molecular orbital that some designed compounds chemical activity similar with TATB, but show better detonation performance. The predicted results reveal that some designed nitrogen-rich compounds outperform traditional energetic materials and may be considered as potential candidates for high-energy materials. Graphical Abstract BRIEFS A series of furazan substituted s-triazine derivatives were designed and investigated theoretically as potential nitrogen-rich high-energy-density materials and most of the compounds exhibit high solid phase heat of information and fascinating detonation properties.

Polymorphic Transition in Traditional Energetic Materials: Influencing Factors and Effects on Structure, Property, and Performance

Polymorphism is universal in energetic materials, and polymorphic transformation (PT) causes variations in the structure, properties, and performance. This article reviews the polymorphs of six tra...

Compatibility study of NaN5 with traditional energetic materials and HTPB propellant components

ABSTRACT Nitrogen-rich and poly-nitrogen energetic materials have the advantages of high density, high formation enthalpy, and environmentally friendly as new energetic materials. Among them, cyclo-N5 − is one of the most representative ionic nitrogen compounds. However, at present, the studies are mainly in the field of synthesis. This study mainly explores the compatibility of NaN5 with traditional energetic materials, hydroxy-terminated polybutadiene (HTPB), and ammonium perchlorate (AP). The compatibility is an important parameter to evaluate the safety and reliability of propellants. Therefore, AP, cyclotetramethylenetetranitramine (HMX), cyclotrimethylenetrinitramine (RDX), hexanitrohexazaisowurtzitane (CL-20), HTPB were selected to study the compatibility of NaN5 in the means of differential scanning calorimetry (DSC). The results show that NaN5/AP, NaN5/HMX, NaN5/RDX, NaN5/CL-20 have good compatibility, whereas NaN5/HTPB exhibits moderate compatibility.

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.

Hydrogen Bonding in CHON-Containing Energetic Crystals: A Review

Hydrogen bonding (HB) universally exists in CHON-containing energetic materials (EMs) and significantly influences their structures, properties, and performances. As time proceeds, some new types of EMs such as energetic cocrystals (ECCs) and energetic ionic salts (EISs) are thriving currently and richening insight into the HB of EMs, and these are reviewed in this article as well. The intramolecular HB mostly exists in stable molecules while seldom in less stable molecules; weak and abundant HBs dominate intermolecular interactions and consolidate crystal packing. For ECCs with neutral heterogeneous molecules, intermolecular HBs serve as one of the strategies for crystal design. In comparison, the HBs in EISs are greatly strengthened as their polarity significantly increases with ionization. A strong intramolecular HB usually enhances molecular stability with large π-bonds and packing coefficients and facilitates reversible H transfer, which is advantageous for low mechanical sensitivity. The intermolecular HB-aided π–π stacking that favors low mechanical sensitivity is observed in all three kinds of EMs, including traditional EMs with neutral homogeneous molecules, ECCs with neutral heterogeneous molecules, and EISs. However, a strong intermolecular HB in an EM causes a ready intermolecular H transfer, thereby worsening thermal stability. Thus, the influence of HBs on the stability of EMs can go both ways, and there should be a balance when new HB-containing EMs are designed.

Ignition and combustion characteristics of aluminum/manganese iodate/nitrocellulose biocidal nanothermites

The traditional energetic materials are insufficient to sterilize the deleterious microorganisms carried by biological weapons completely. Three kinds of biocidal energetic composites were investigated herein: (1) aluminum/manganese iodate/nitrocellulose (Al/Mn(IO3)2/NC) composite microspheres prepared by electrospray, (2) Al/Mn(IO3)2/NC nanocomposites prepared by physical mixing, and (3) Al/Mn(IO3)2 nanothermites prepared by physical mixing. The thermal decomposition process of Mn(IO3)2 was studied by thermogravimetry–differential scanning calorimetry-mass spectrometry (TG/DSC-MS) at a low heating rate of 5 °C min−1, and T-jump/time-of-light mass spectrometry (T-jump/TOFMS) at a high heating rate of ~ 5×105 °C s−1. The ignition temperatures of three energetic composites were measured in a T-jump gas chamber (Ar, 1 atm) by a high-speed camera. The combustion performance of three energetic composites was investigated in a constant-volume combustion cell. The results show that Al/Mn(IO3)2/NC composite microspheres prepared by electrospray have a better ignition (lower ignition temperature) and combustion (higher pressurization rate and peak pressure) performances than the other two prepared composites. The thermal performances of these composite microspheres also overshadow the documented energetic composites such as Al/AgIO3, Al/KIO4, and Al/NaIO4 nanothermites. The MS results at high heating rates demonstrate the production of I2 from the thermite reaction, potentiating Al/Mn(IO3)2/NC as an energetic formulation for biocidal applications.

Preparation and characterization of ethane-1,2-diaminium trinitromethanide as a novel energetic ionic liquid

In the present research, ethane-1,2-diaminium trinitromethanide ([NH3C2H4NH3][C(NO2)3]2) as a novel energetic dicationic ionic liquid (EDIL) was synthesized in a simple manner. The synthesized [NH3C2H4NH3][C(NO2)3]2 was characterized using FT-IR, Mass, 1H NMR, 13C NMR and DSC analysis. [NH3C2H4NH3][C(NO2)3]2 showed good thermal stability and decomposition enthalpy, which is significant compared to traditional energetic materials such as 1,3,5-Trinitro-1,3,5-triazinane (RDX) and 1,3,5,7-Tetranitro-1,3,5,7-tetrazocane (HMX). Also, a number of computational approaches such as electrostatic maps, electron density properties, enthalpy of formation and volumetric for [NH3C2H4NH3][C(NO2)3]2 were explored. The interaction energy and structural parameters of the prepared DIL is estimated at M06-2X/6–311++G (2d,2p) level of theory.

Crystal Engineering for Creating Low Sensitivity and Highly Energetic Materials

Energy and safety are the two most important concerns of energetic materials (EMs), while they usually contradict each other: the high energy typically goes together with low safety. Low sensitivity and highly energetic materials (LSHEMs) balance well the energy and safety and thus are highly desired for extensive applications. Nevertheless, on the whole, the energy–safety contradiction, the energy and component limits, and insufficient knowledge about the relationships among components, structures, and properties and performances of EMs have made the development of LSHEMs, or even the entire group of EMs, evolve slowly. This Perspective focuses upon the current progress in the clarifications of the energy–safety contradiction and the crystal packing–impact sensitivity relationship of EMs. Also, we propose strategies for creating new LSHEMs or desensitized EMs through crystal engineering, covering traditional EMs composed of neutral single-component molecules, energetic cocrystals, and energetic ionic sal...