Properties Of Energetic Materials Research Articles

Study of the relationship between pressure and sensitivity of energetic materials based on first-principles calculation.

In order to study the relationship between the sensitivity and pressure of energetic materials, six kinds of energetic materials were selected as the research object. The crystal structure, electronic, and phonon properties under hydrostatic pressure of 0 ~ 45 GPa were calculated by first principles. The calculation results show that the lattice parameters and band gap values of these six energetic materials decrease with the increase of pressure. The peak of the density of states decreases and moves to the low energy direction, and the electrons become more active. Meanwhile, the effect of pressure on the sensitivity of the energetic materials is analyzed based on the multi-phonon up-pumping theory. The number of doorway modes and integral of projected phonon density of states under high pressure is calculated. The results show that both of them increase with the increase of pressure. And the smaller the value of the band gap, the larger the number of doorway modes and integral of projected phonon density of states, and the more sensitive the energetic material is. All calculations are performed using the Materials Studio software based on density functional theory. The Perdew-Burke-Ernzerhof (PBE) functional of the generalized gradient approximation (GGA) is used to calculate the exchange correlation function, and the Grimme dispersion correction method is used to deal with the weak intermolecular interaction. The structure of the compound was optimized by BFGS algorithm. The linear response is used to calculate the phonon properties of energetic materials. The plane wave cutoff energy was set to 830eV. The K-point grids of TATB, FOX-7, TNX, RDX, TNT, and HMX were chosen as 2 × 2 × 2, 2 × 2 × 1, 2 × 1 × 1, 1 × 1 × 1, 1 × 2 × 1, and 2 × 1 × 2.

A new crystal form of Hx2TNBI·2H2O through solvent-induced crystallization

Polymorphism is universal in energetic materials (EMs), which is originated from the differences of molecular conformers and stacking mode. The polymorphic transition may lead to the change of crystal structure and properties of EMs. In this work, β-Hx2TNBI·2H2O (β-1) was successfully synthesized through solvent-induced conformational transition of Hx2TNBI·2H2O. From the perspective of quantum chemistry and molecular dynamics, the crystal stacking changes caused by different molecular conformations are discussed in detail, which leads to the properties difference of EMs. The results show that β-1 featured wave-like crystal stacking, making it less sensitive to external mechanical stimuli than α-Hx2TNBI·2H2O (α-1) (α-1: IS > 6 J, FS > 288 N; β-1: IS > 20 J, FS > 360 N). α-1 featured better the aromaticity, which gives it higher thermal stability than β-1 (α-1: Td = 186 °C; β-1: Td = 146 °C). Simultaneously, compared with β-1, α-1 has higher crystal density and detonation performance. This work provides a new and effective way to change the safety of EMs.

Methodology for Studying Combustion of Solid Rocket Propellants using Artificial Neural Networks

The combustion properties of energetic materials have been extensively studied in the scientific literature. With the rapid advancement of data science and artificial intelligence techniques, predicting the performance of solid rocket propellants (SRPs) has become a key focus for researchers globally. Understanding and forecasting the characteristics of SRPs are crucial for analyzing and modeling combustion mechanisms, leading to the development of cutting-edge energetic materials. This study presents a methodology utilizing artificial neural networks (ANN) to create multifactor computational models (MCM) for predicting the burning rate of solid propellants. These models, based on existing burning rate data, can solve direct and inverse tasks, as well as conduct virtual experiments. The objective functions of the models focus on burning rate (direct tasks) and pressure (inverse tasks). This research lays the foundation for developing generalized combustion models to forecast the effects of various catalysts on a range of SRPs. Furthermore, this work represents a new direction in combustion science, contributing to the creation of a High-Energetic Materials Genome that accelerates the development of advanced propellants.

Recent application of porous materials in explosives: A mini-review

Nowadays, porous structures have exhibited many novel characteristics in the microstructure design of energetic materials, which possesses a unique impact on the macroscopic properties of energetic materials, and thus have exhibited a wide range of application prospects. In this review, several typical porous structures were introduced from the aspects of synthesis, performance and structure, and the main research progress of porous structures applied to the design of energetic materials in recent years was reviewed. Specifically, this article discussed the impact of nanopores, ordered structures and high specific surface areas on the safety and energy release of typical energetic materials, and focused on research area including the explosive adsorption and detection, new host-guest explosives, and new porous energetic materials. At the end of the review, an outlook and discussion were provided on the development trend of the combination of porous structure and explosives.

Bio-inspired design of PTFE/B energetic materials with high reactivity and flexibility

Although new-type energetic materials have been investigated extensively, there is a challenge on how to integrate energy density and mechanical properties of energetic materials simultaneously. Herein, a versatile approach was proposed to design energetic materials with high energy density, reactivity, and flexibility based on a bio-inspired strategy. By mimicking the “brick-and-mortar” structure within a natural nacre, the energetic film with alternative layers of polytetrafluoroethylene (PTFE) and boron (B) was successfully fabricated. The nacre-mimetic PTFE/B energetic film exhibited excellent reaction heat (4413.9 J g−1) and bright combustion flame, which may originate from the exothermic reaction mechanism between fluorine (F) and B. Even more remarkably, such PTFE/B energetic film revealed prominent mechanical flexibility reported for the first time. These findings indicate that the nacre-mimetic strategy provides an effective route to engineer energetic materials with high energy density, reactivity, and flexibility.

Modification of an N-Methyl Group toward a New Energetic Melt-Castable Material with a Good Energy-Stability Balance

AbstractThe energy and stability properties of energetic materials are often contradictory to each other (e.g., high energy vs low thermal stability). There is no doubt that it is still challenging to explore the effective balance between energetic performance and molecular stability, especially for melt-castable materials. In this study, we selected the 4-methoxy-3,5-dinitropyrazole framework and a stable nitro group to design a new energetic melt-castable compound, namely 4-methoxy-3,5-dinitro-1-(nitromethyl)-1H-pyrazole (MDNNMP). Compared with the N-methylation product DMDNP and the nitrato-substituted derivative MC-7, MDNNMP exhibits a better balanced performance, including good thermal stability (Td : 203.7 °C), detonation velocity (Dv : 8099 m s–1) and impact sensitivity (20 J). The favorable balanced performance of MDNNMP suggests that it is a suitable candidate as a high-performance melt-castable material. Additionally, compared with the nitratomethyl group, the nitromethyl group demonstrates superior advantages in performance regulation.

Azo-linked four-heterocyclic energetic molecule and its complexes: Exploring the important influence of conjugated planar structure on their crystal arrangement and stability

Using two routes, this study designed and synthesized a novel azo-linked four-heterocyclic compound, 1,2-bis(5-(1H-tetrazol-5-yl)-4H-1,2,4-triazol-3-yl) diazene (3, H4BTTD), with high yields. It corroborated that large conjugated planar energetic molecules in energetic compounds, exemplified by H4BTTD, contribute to the formation of layered crystal stacking based on abundant hydrogen bonds and interlayer π-π interactions. This markedly diminishes the mechanical sensitivities of energetic compounds. Single-crystal X-ray diffraction (XRD) experiments revealed the presence of layered structures in H4BTTD hydrate, as well as its magnesium-based complex [Mg2(BTTD)(H2O)8] (4) and calcium salt [Ca(H2O)7] (H3BTTD)2(5). Based on these structural data, this study analyzed the causes of these layered structures. Furthermore, this study systematically characterized the compounds’ physical and chemical properties, including mechanical sensitivities (IS ≥ 20 J, FS > 360 N), thermal stability (Td = 253.7–287.8 °C), and detonation performance (D = 6808–8253 m⋅s−1), confirming the influence of molecular structures on the macroscopic properties of energetic materials through crystal stacking. Additionally, pyrotechnic formulas based on compounds 3 and 5 exhibited the most intense light emission within a wavelength range of 658.6–689.8 nm, underscoring the potential application of both compounds as promising candidates in preparing high-purity red pyrotechnic formulation.

Pressure‐assisted binder jetting for additive manufacturing of mock energetic composites

AbstractAdditive manufacturing (AM) has emerged as a promising approach to achieve energetic materials (EMs) with intricate geometries and controlled microstructures, which are crucial for safety and performance optimization. However, current AM methods still face limitations such as limited densities and inadequate solids loading. To overcome these limitations, we have developed a pressure‐assisted binder jet (PBJ) process that has the potential to allow for the fabrication of intricate EMs while preserving their desired properties. This study aims to investigate the effects of printing parameters on the microstructures and properties of EMs, including density, solids loading, mechanical properties, and heterogeneity. Our results demonstrate that the PBJ process achieves exceptional properties in EMs, including densities up to 83.4 % and solids loading up to 95.4 %, surpassing those achieved by existing AM processes. Furthermore, the mechanical properties of the fabricated EMs are comparable to those achieved using conventional fabrication techniques, including a compressive strength of 3.32 MPa, a Young's modulus of 16.68 MPa, a Poisson's ratio of 0.45, a shear modulus of 5.73 MPa, and a bulk modulus of 21.01 GPa. Various test cases were printed to showcase the ability of the PBJ process to create EMs with complex structures and exceptional properties. Micro‐computed tomography was employed to analyze the influence of printing parameters on the internal composition and microstructures of the printed specimens.

Effects of oxidant molecules on the thermal decomposition of 4,7‐diaminopyridazino[4,5‐c]furanoxane crystal: Ab initio molecular dynamics simulations

AbstractInserting oxidant molecules into the crystal voids to form oxidant cocrystal can greatly enhance the detonation properties of energetic materials. Therefore, oxidant cocrystals are regarded as one type of potential candidates of high energy density materials. The effects of the oxidants (HNO3 and HClO4) on the thermal decomposition mechanisms of two oxidant cocrystals (DPF(4,7‐diaminopyridazino[4,5‐c] furanoxane):HNO3 and DPF:HClO4) were investigated by ab initio molecular dynamics (AIMD). AIMD simulations are performed using a NVT ensemble. The temperature was controlled by a Nosé thermostat. First, we performed 5 ps simulations at 298.15 K to get an equilibrium system. Then, the simulations were performed at 3000 K with a time step of 1 fs and a total time of 15 ps. The initial degradation pathways of the two cocrystals have the same and involve the cleavage of the N–H and N–O bonds. Five different decay pathways were found in the subsequent reactions: intermolecular H transfer, N–O bond cleavage, N–N bond cleavage, and C–C bond formation and cleavage. Both HNO3 and HClO4 can promote the formation of N2, H2O and CO2, but only have a certain effect. Different oxidant molecules hardly affect the initial and subsequent decomposition paths of DPFH.

Machine learning-based prediction and interpretation of decomposition temperatures of energetic materials

Exploring the application of machine learning (ML) in energetic materials (EMs) has been a hot research topic. Accordingly, the prediction of the detonation properties of EMs using ML methods has attracted much attention. However, the predictive models for the thermal decomposition temperatures (Td) of EMs have been scarcely reported. Furthermore, the small datasets used in these reports lead to a weak generalization ability of the predictive models. This study created a dataset containing 1022 energetic molecules with Td values of 38–425 ​°C and determined an optimal predictive model through training. The gradient boost machine for regression (GBR) model yielded a coefficient of determination (R2) of 0.65 and a mean absolute error (MAE) of 27.7 for the test set. This study further explored critical features, determining that the prediction accuracy of the models was significantly influenced by descriptors representing molecular bond stability (i.e., the BCUT metrics) and atomic composition (i.e., the Molecular ID). Finally, the analysis of the outlier structure indicated that the model accuracy can be further improved by incorporating features related to molecular interactions. The results of this study help gain a deep understanding of the application of ML in the prediction of EM properties, particularly in dataset construction and feature selection.

Comparative study on the unimolecular decompositions of energetic regioisomers: BFTF-1 and BFTF-2

Regioisomeric energetic materials displayed different properties and performances. Understanding the regioisomerism in energetic materials and how it impacts the properties of energetic materials could provide insights into their improvements and designs. The present study explored the electrostatic properties for two regioisomers of energetic material, 3,4-bis(3-fluorodinitromethylfuroxan-4-yl)furoxan (BFTF-1) and 3,4-bis(4-fluorodinitromethylfuroxan-3-yl)furoxan (BFTF-2), which differ in the orientations of N-oxides in the furoxan rings on both sides. The strengths for corresponding covalent bonds in both isomers appeared to be similar, while the intramolecular interactions were distinctively different due to regioisomerism. The proposed decomposition pathways predicted from quantum mechanics (QM) calculations showed that BFTF-1 and BFTF-2 shared similar decompositions of nitro moieties in fluorodinitromethyl groups and furoxan ring openings followed by CC bond breakage. Both isomers also displayed different furoxan ring opening involving neighboring groups due to regioisomerism. The reactive molecular dynamics simulations confirmed that NO2 would be the initial products for both isomers and the species of molecules in their final products are similar. The present study provided insights into understanding the regioisomerism affecting the thermal decompositions of isomeric energetic materials and laid the ground for further improvements and designs.

Theoretical Kinetic Studies on Thermal Decomposition of Glycerol Trinitrate and Trimethylolethane Trinitrate in the Gas and Liquid Phases.

Glycerol trinitrate (NG) and trimethylolethane trinitrate (TMETN), as typical nitrate esters, are important energetic plasticizers in solid propellants. With the aid of high-precision quantum chemical calculations, the Rice-Ramsperger-Kassel-Marcus (RRKM)/master equation theory and the transition state theory have been employed to investigate the decomposition kinetics of NG and TMETN in the gas phase (over the temperature range of 300-1000 K and pressure range of 0.01-100 atm) and liquid phase (using water as the solvent). The continuum solvation model based on solute electron density (SMD) was used to describe the solvent effect. The thermal decomposition mechanism is closely relevant to the combustion properties of energetic materials. The results show that the RO-NO2 dissociation channel overwhelmingly favors other reaction pathways, including HONO elimination for the decomposition of NG and TMETN in both the gas phase and liquid phase. At 500 K and 1 atm, the rate coefficient of gas phase decomposition of TMETN is 5 times higher than that of NG. Nevertheless, the liquid phase decomposition of TMETN is a factor of 5835 slower than that of NG at 500 K. The solvation effect caused by vapor pressure and solubility can be used to justify such contradictions. Our calculations provide detailed mechanistic evidence for the initial kinetics of nitrate ester decomposition in both the gas phase and liquid phase, which is particularly valuable for understanding the multiphase decomposition behavior and building detailed kinetic models for nitrate ester.

Desensitization of CL‐20/HMX Co‐Crystal by Functionalized Graphene Oxide

AbstractInterface interaction has always been considered a major challenge in the field of desensitization. Co‐crystal explosives can balance the properties of energetic materials, but their limited desensitization effect limits their further practical applications. Based on this, we proposed the desensitization of CL‐20/HMX co‐crystal by three functionalized graphene oxide (NH2‐GO, Am‐GO and M550‐GO). The sensitivity results indicate that the M550‐GO has the best desensitization. To further explore the reasons for the better desensitization effect of M550, molecular dynamics was used to simulate the binding energy and mechanical properties of different systems. The results showed that the electrostatic interaction between functionalized graphene oxide and CL‐20/HMX co‐crystal can enhance the interfacial interaction more than van der Waals force. In a word, this work provides new ideas and insights for enhancing the interface interaction of coating materials and popularizing the practical application of co‐crystal explosives.

Thermal Properties of Energetic Materials—What Are the Sources of Discrepancies?

Thermal analysis is widely used to investigate the properties of a variety of energetic materials, including the mutual compatibility of components of energetic material mixtures. Although thermal analysis methods are a valuable source of information about energetic materials, their use requires careful consideration of the employed methodology, as well as an understanding of the thermally induced processes taking place within energetic materials. Several case studies involving the study of energetic materials are presented, in order to highlight some of the most relevant issues in the application of thermal analysis methods. Some recommendations about the application of thermal analysis methods and accompanying methodologies for estimating other properties of energetic materials are also included.

Modulation of Crystal Growth of an Energetic Metal–Organic Framework on the Surfaces of Graphene Derivatives for Improved Detonation Performance

Energetic materials are a special class of energy materials composed of C, H, O, and N. Their safety always deteriorates with increasing energy. Regulating the properties of energetic materials to meet application requirements is one of the focuses of research in this field. Energetic metal-organic frameworks (EMOFs) are good candidates as primary explosives to replace lead azide (LA) and other explosives containing toxic metal elements. However, safety remains the biggest concern in applications. In this paper, crystal morphology modulation of EMOF was carried out by stepwise coordination of metal ions and energetic ligands on surfaces of graphene oxide (GO) and amino-functionalized graphene oxide (AGO). Two energetic composite materials, Cu-AFTO@GO and Cu-AFTO@AGO, were successfully synthesized and also the EMOF (Cu-AFTO). The structures and morphologies of these materials were fully characterized. The thermal decomposition behaviors, mechanical sensitivity, and electrostatic discharge sensitivity were investigated in detail. The electric ignition ability of EMOF and two composite materials was tested. This study shows that it is possible to reduce the diameter of EMOF crystals from hundreds of microns to tens of nanometers by a stepwise coordination method. The high electrical conductivity and sensitivity-reducing effect of GO and/or AGO allow the nanosized EMOF crystals to have a lower ignition threshold and lower sensitivity.

Highly Selective Nitroamino Isomerization Guided by Proton Transport Dynamics: Full-Nitroamino Imidazole[4,5-d]pyridazine Fused-Ring System.

Due to the advantage of the hydrogen bond system formed by nitroamino isomerization, by the calculations of hydrogen transfer in reported nitroamino explosives, the proton transport dynamics was first proposed to predict the nitroamino isomerization of energetic materials. With the calculated results of zero-point energy, the full-nitroamino fused energetic materials, 2,4-nitroamino-7-nitroimino-1,5-dihydro-4H-imidazolo[4,5-d]pyridazine (FNPI-1) and 2,2',7,7'-tetranitromino-4,4'-azo-imidazolo[4,5-d]pyridazine (FNPI-2) were designed and successfully synthesized. The highly selective nitroamino isomerization of neutral compound FNPI-1 is shown by X-ray diffraction. After the hydrogen transfer occurs, the intermolecular hydrogen bonds will greatly promote tight stacking, which enhances the density and thus a series of comprehensive properties of energetic materials. The theoretical calculations of zero-point energy explain perfectly the selectivity of hydrogen transfer between the nitroamino groups and the fused-ring skeleton for FNPI-1. The hydrogen atom transfer and selective isomerization of nitroamino energetic materials can be accurately predicted following proton transport dynamics, which provides computational bases and new ideas for the efficient design of fully nitroamino-based explosives.

Amino‐group excites vitality in nitrogen‐rich energetic salts of triazolium

AbstractIncorporating amino groups is an efficient strategy for the tuning properties of energetic materials. However, there is no unanimous conclusion on the effect of the number of amino groups (−NH2) on performance. Therefore, in this study, different number of −NH2 of four energetic salts of triazolium based on oxadiazole and triazole were designed and synthesized. The structure features of energetic salts 4–6 were then investigated by single‐crystal X‐ray diffractions and Hirshfeld surfaces analyses. Afterward, the effects of −NH2 were evaluated by thermal stability, impact sensitivity and detonation performance. All these energetic salts were insensitive to mechanical stimulation (IS >40 J), but the thermal decomposition temperatures of energetic salt 5–7 with −NH2 are 24 °C to 54 °C higher than energetic salt 4 without −NH2. Moreover, energetic salt 5 with one −NH2 has the highest theoretical detonation properties compared to those without −NH2 (4) and with two −NH2 (6, 7). These observations revealed that appropriate amount of −NH2 can lead to desirable increase in the energetic properties, and this work can offer guidance for the design and synthesis of further energetic salts.

Editorial

Editorial

Effects of oxidizing molecules on the thermal decomposition of TTDO by ab initio molecular dynamics simulations

Oxidizing molecules play a very important role in improving the comprehensive properties of energetic materials. Recently, a series of energetic cocrystals containing 2,4,6-triamino-1,3,5-triazine-1,3-dioxide (TTDO) and oxidizing molecule have been successfully prepared. Therefore, ab initio molecular dynamics were used to simulate the thermal decomposition process of TTDO, TTDO:H2O2, TTDO:HNO3, and TTDO:HClO4 crystals at 3000 K to study the role of oxidizing molecules during the thermal decomposition of TTDO. The initial decomposition paths of the TTDO crystal include N–H bond breaking, C–N bond breaking, and intramolecular and intermolecular H transfers. The formation mechanisms of H2O, N2, and CO2 in the four crystals are completely different. The key formation mechanism of H2O is the combination of O with OH, that of N2 is the formation of the -N-N- structure, and that of CO2 is to form the intermediate CO-R with carbonyl structure that form the fragment with the -O-C-O- structure. All the oxidizers H2O2, HNO3, and HClO4 involve in the formation of H2O, N2, and CO2. The formation mechanisms of urea during the decomposition process of the four crystals are completely different, but the key step is to produce the structure of -N–CO–N-. An analysis of Nx shows that H2O2, HNO3 and HClO4 affect not only the types of Nx, but also its formation mechanisms. Among them, HNO3 has the greatest influence on Nx.

Constructing Planar C–N Bond-Linked Bi-Triazole High-Energy Explosives via the Formation of Salts

Abstract Energy and safety are the two most concerning properties of energetic materials (EMs). Design and synthesis of planar molecules is considered to be an effective way to obtain high-energy low-sensitivity EMs. In this study, a new C–N bond-linked energetic bi-triazole compound, 3,4′,5-triamine-1,3′-bi(1,2,4-triazole) (1), and its nitrate (1a) and perchlorate salt (1b), as well as a nitrification product, 5-amino-3,4′-dinitramide-1,3′-bi(1,2,4-triazole) (2), and corresponding sodium (2a) and potassium salt (2b) were designed and synthesized. All compounds were fully characterized. The molecular structures of 1, 1a, 1b, 2a, and 2b were confirmed by single-crystal X-ray structure analyses. It was found that 1 exhibits non-planar loose molecular stacking, while 1a, 1b, and 2b exhibit compact face-to-face layered molecular packing structures, and salt 2a exhibits compact wave-like stacking. The physicochemical properties of all compounds, such as density, thermal stability, and mechanical sensitivity, were studied. 1, 1a, 1b, 2a, and 2b have low impact and friction sensitivity and good thermal stability. In addition, Hirshfeld surfaces (HS), independent gradient model (IGM) analyses combined with single-crystal analyses revealed intermolecular interactions in 1, 1a, 1b, 2a, and 2b and clarified the relationship between the structures and molecular properties. The sophisticated hydrogen bonds between the bi-triazole molecules and nitrate/perchlorate ions are the driving force of formation of planar structures. Detonation properties calculated with the professional software package EXPLO5 showed that nitrate 1a (D = 8872 m·s−1, P = 34.8 GPa) and perchlorate 1b (D = 8956 m·s−1, P = 35.1 GPa) exhibit good detonation performance.