Advances in science and technology of modern energetic materials: an overview

Relationship between Energetic Performance and Clustering Effects on Incremental Nitramine Groups: A Theoretical Perspective

Nitramine compounds are typical high-energy-density materials (HEDMs) and are widely used as explosives because of their superior explosive performance over conventional energetic materials. In this work, the thermal properties of 1-nitropiperidine (NPIP), 1,4-dinitropiperazine (DNP), and 1,3,5-trinitro-1,3,5-triazinane (RDX) were investigated from quantum mechanics (QM) and reactive force field (ReaxFF) molecular dynamics simulations. We found that the bond dissociation energy of the N-NO₂ bond, heat of formation, released energy, produced fragments, and oxygen balance are closely related to the incremental nitramine group. The nitramine group has a significant effect on the energetic performance of these nitramine compounds. In addition, the increase of the nitramine group will improve thermal decomposition activity, promote the generation of small molecules, and restrain the formation of carbon clusters. We hope that this work can shed new light on the design of energetic materials.

From BTO2− to HBTO− insensitive energetic salt: a route to boost energy

A promising strategy was utilized to boost the detonation performance of insensitive energetic salts.

Revisiting the reactive chemistry of FOX-7: cyclization of FOX-7 affords the fused-ring polynitro compounds

A new FOX-7 derivatization strategy was developed to synthesize fused-ring and cyclic polynitro compounds, which enriches the unpredictable reactive chemistry of FOX-7.

Fe(ii)-Catalyzed azidation of polybutadienes using the Zhdankin reagent

Phenyl-terminated polybutadienes (PtPBs) are efficiently converted to azidated PtPBs using the Zhdankin reagent generated in situ from iodosobenzoic acid and TMSN₃ with an iron catalyst.

Preparation of CL-20/TFAZ cocrystals under aqueous conditions: balancing high performance and low sensitivity

CL-20/TFAZ cocrystal explosives were prepared by a self-assembly method under aqueous conditions with both low sensitivity and high detonation performances.

Organic chelate-free and azido-rich metal clusters and coordination polymers from the use of Me3SiN3: a new synthetic route to complexes with beautiful structures and diverse magnetic properties

A new synthetic route to structurally novel and magnetically interesting 3d-metal azido clusters and coordination polymers is presented; the key reagent for the preparation of solely azido-bridged molecule-based species is the organic azide precursor Me₃SiN₃.

Synthesis, characterization and properties of a novel energetic ionic salt: dicarbohydrazide bis[3-(5-nitroimino-1,2,4-triazole)]

DCBNT, a new compound, exhibits low friction and impact sensitivities, good thermal stability, and promising detonation pressure and detonation velocity.

Toward reliable characterization of energetic materials: interplay of theory and thermal analysis in the study of the thermal stability of tetranitroacetimidic acid (TNAA)

The thermal stability of energetic materials, being of the utmost importance for safety issues, is often considered in terms of kinetics, e.g., the Arrhenius parameters of the decomposition rate constant. The latter, in turn, are commonly determined using conventional thermoanalytical procedures with the use of simple Kissinger or Ozawa methods for kinetic data processing. However, thermal decomposition of energetic materials typically occurs via numerous exo- and endothermal processes including fast parallel reactions, phase transitions, autocatalysis, etc. This leads to numerous drawbacks of simple approaches. In this paper, we proposed a new methodology for characterization of the thermochemistry and thermal stability of melt-cast energetic materials, which is comprised of a complementary set of experimental and theoretical techniques in conjunction with a suitable kinetic model. With the aid of the proposed methodology, we studied in detail a novel green oxidizer, tetranitroacetimidic acid (TNAA). The experimental mass loss kinetics in the melt was perfectly fitted with a model comprised of zero-order reaction (sublimation or evaporation) and first-order thermal decomposition of TNAA with the effective Arrhenius parameters Ea = 41.0 ± 0.2 kcal mol-1 and log(A/s-1) = 20.2 ± 0.1. We rationalized the experimental findings on the basis of highly accurate CCSD(T)-F12 quantum chemical calculations. Computations predict that thermolysis of TNAA involves an intricate interplay of multiple decomposition channels of the three tautomers, which are equilibrated via either monomolecular reactions or concerted double hydrogen atom transfer in the H-bonded dimers; the calculated Arrhenius parameters of the effective rate constant coincide well with experiment. Most importantly, calculations provide detailed mechanistic evidence missing in the thermoanalytical experiment and explain formation of the experimentally observed primary products N2O and NO2. Along with the kinetics and mechanism of decomposition, the proposed approach yields accurate thermochemistry and phase change data of TNAA.

Preparation of a superfine RDX/Al composite as an energetic material by mechanical ball-milling method and the study of its thermal properties

To research the influence of aluminum (Al) on the decomposition of 1,3,5-trimethylene trinitramine (RDX), a type of superfine RDX/Al composite as an energetic material with a mass ratio of 70/30 was successfully prepared by mechanical ball-milling method. The morphology and structure of the superfine RDX/Al composite were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The thermal decomposition properties were analyzed by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC), and thermal-infrared spectrometry (DSC-FTIR) online. The results showed that the as-prepared material was a type of a novel superfine composite with the superfine RDX particles coated on the surface of Al flakes. XPS analysis indicated that a new Al-N bond was formed in the superfine RDX/Al composite and both physical and chemical absorptions existed between RDX and Al at the same time. The thermal decomposition temperature of RDX in the superfine RDX/Al composite had a shift of about 50 °C towards the lower temperature range compared with that of the neat superfine RDX when tested at four heating rates of 5, 15, 25 and 35 °C min-1. Its activation energy value also decreased to 70.8 kJ mol-1 compared with that of the neat superfine RDX (119.6 kJ mol-1). Moreover, thermal sensitivity of the superfine RDX/Al composite increased. DSC-FTIR analysis showed that the main decomposition products of the superfine RDX/Al composite were N2O and CO2 with nearly no NO and NO2 detected. The formation of Al-N bond and reactive Al atoms are the main reasons for the notably advanced decomposition of RDX in the superfine RDX/Al composite.

Simulation of GAP/HTPB phase behaviors in plasticizers and its application in composite solid propellant

Dissipative particle dynamics and molecular simulations were carried out to investigate the phase behaviors of glycidyl azide polymer (GAP)/hydroxyl-terminated polybutadiene (HTPB) polymer blend in dioctyl sebacate (DOS), and mixture of DOS and bis(2,2-dinitropropyl)formal/acetal (A3), respectively. The rheology of GAP/HTPB propellant slurry plasticized by A3/DOS was studied. First, single-phase aggregations of GAP and HTPB appear slightly in A3/DOS whereas it is conspicuous in DOS, which results from the small surface tension between the GAP/HTPB plasticized by A3/DOS and the weak thermal diffusion of this blend. Furthermore, with the plasticizing ratio (po/pl) increasing to 1.2, the GAP/HTPB propellant slurry plasticized by A3/DOS exhibits small viscosity and yield stress, and the Newtonian-like behavior of slurry improves its manufacturability. Finally, integral GAP/HTPB-based propellant can be obtained using A3/DOS as plasticizers.

Comparative studies on structure, sensitivity and mechanical properties of CL-20/DNDAP cocrystal and composite by molecular dynamics simulation

Molecular dynamics simulation was performed on 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), 2,4-dinitro-2,4-diazapentane (DNDAP), and CL-20/DNDAP cocrystal and composite under COMPASS force field at different temperatures. The binding energy (E_bind), radial distribution function (RDF), trigger bond length, cohesive energy density (CED) and mechanical properties were studied and compared. The results show that the binding energy of the cocrystal is evidently higher than that of the composite at the same temperature. RDF analysis reveals that hydrogen bonds and vdW forces between CL-20 and DNDAP exist in both CL-20/DNDAP cocrystal and composite, and the interactions in the cocrystal are stronger than those in the composite. The maximum trigger bond length decreases in the order ε-CL-20 > CL-20/DNDAP composite > CL-20/DNDAP cocrystal. Moreover, the rigidity and stiffness of the cocrystal and composite decrease compared to that of CL-20, while the ductility and elasticity are better than that of the two pure components. These results demonstrate that CL-20/DNDAP cocrystal might be very promising in explosive applications.

This work proves that cocrystallization is a more effective modification method than mixing and elucidated the underlying mechanism.

High-Energy Nitramine Explosives: A Design Strategy from Linear to Cyclic to Caged Molecules

After carefully analyzing the Kamlet-Jacobs (K-J) equations and the structural traits of well-known explosives, hexahydro-1,3,5-trinitro-1,3,5-triazin (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), and hexanitrohexaazaisowurtizitane (CL-20), diverse nitramine explosives including linear (Models IAn, IBn, and ICn), cyclic (Model IIn), and caged (Models IIIAn and IIIBn) molecules were designed by incorporating various number (n) of -CH2NNO2- structural unit and studied using the B3LYP/6-31G* and B3PW91/6-31G** methods of the density functional theory. Computational results show that all of the energetic parameters, that is, density (ρ), detonation velocity (D), and detonation pressure (P), follow the order of IIIBn > IIIAn > IIn > IAn > IBn > ICn. With the increasing n, the D and P of linear nitramines eventually keep stable. This clearly indicates that elongating the chain length (e.g., polymerization) brings little or even negative benefit in boosting the explosive properties. The oxygen balance and the K-J equation parameter ϕ both have a significant influence on the detonation properties. Caged compound IIIA2 has not only comparable energetic properties but also better sensitivity and thermal stability than CL-20.

A nitrogen-rich ligand as a scaffold for slow magnetic relaxation in dysprosium-based 0D and 1D architectures

A recently designed nitrogen-rich ligand is successfully applied as a scaffold for lanthanide ions to show that the intricate chemistry of energetic materials can be combined with other fields of research, including that of molecular magnetism. Herein, we report the synthesis of two different types of molecular architectures using a single ligand template, in which the discrete monomer exhibits single-molecule magnet-like behaviour along with two well-isolated modes of magnetic relaxation.

A Critical Review on Advances in the Multicomponent Synthesis of Pyrroles

Nitrogen containing heterocyclic compounds are biologically significant molecules. This is especially true for pyrrole a five membered nitrogen containing aromatic molecule, which is present as a key structural motif in a large number of drugs and lead molecules. This review aims to provide an overview of the multi-component reaction (MCR) based methodologies used for the synthesis of pyrrole and its derivatives, focusing particularly on eco-friendly methods that avoid the use of hazardous reagents, solvents and catalysts are deemed especially relevant to the disciplines of medicinal chemistry and drug discovery.

Synthesis, crystal structure and thermal properties of an unsymmetrical 1,2,4,5-tetrazine energetic derivative

A new unsymmetrical s-tetrazine derivative, namely 4-({2-[6-(3,5-dimethyl-1H-pyrazol-1-yl)-1,2,4,5-tetrazin-3-yl]hydrazin-1-ylidene}methyl)phenol (DPHM), C₁₄H₁₄N₈O, was synthesized based on 3-(3,5-dimethylpyrazol-1-yl)-6-hydrazinyl-s-tetrazine (DPHT). The structure was characterized by elemental analysis and single-crystal X-ray diffraction. Crystal structure determination shows that DPHM crystallizes in the monoclinic P2₁/c space group with high coplanarity and a zigzag layered structure. In addition, its thermal behaviour was investigated by DSC and TG-DTG methods. The thermal safety of DPHM was evaluated by self-accelerating decomposition temperature (T_SADT), critical temperature of thermal explosion (T_b), entropy of activation (ΔS⁼), enthalpy of activation (ΔH⁼) and free energy of activation (ΔG⁼). Meanwhile, the kinetic parameters and specific heat capacity of DPHM were also determined. The results show that DPHM has better stability and detonation properties than 3-(2-benzylidenehydrazin-1-yl)-6-(3,5-dimethylpyrazol-1-yl)-s-tetrazine (DAHBTz), due to the introduction of a hydroxy group, which increases the number of hydrogen-bond interactions and improves the stability and density of DPHM. This study demonstrates that the performance of an explosive can be optimized through structural modification.

Surface-promoted hydrolysis of 2,4,6-trinitrotoluene and 2,4-dinitroanisole on pyrogenic carbonaceous matter

This study investigates the fate of sorbed nitroaromatics on the surface of pyrogenic carbonaceous matter (PCM) to assess the feasibility of a PCM-promoted hydrolysis. The degradation of two nitroaromatic compounds, 2,4,6-trinitrotoluene (TNT) and 2,4-dinitroanisole, was observed at pH 7 in the presence of graphite powder, a model PCM. By contrast, no decay occurred without graphite. Using TNT as a model compound, our results suggest that TNT decay demonstrated a strong pH dependence, with no reaction at pH 3-5 but rapid degradation at pH 6-10. Moreover, by fitting TNT decay at different pH conditions along with its sorption kinetics to the Langmuir Kinetic Model, our results suggest that the base-catalyzed hydrolysis was important. The activation energy for TNT decay was obtained by measuring reaction rates at different temperatures with or without graphite and no significant difference was observed. However, the addition of tetramethylammonium cation was able to promote TNT decay possibly due to its ability to attract more OH^- from the aqueous solution, leading to an increase in the sorbed OH^- concentrations. Nitrite and a Meisenheimer complex were identified as degradation products for TNT. Other PCM, such as biochar, also demonstrated a comparable ability in promoting TNT decay at pH 7. Furthermore, a rapid degradation of TNT at pH 7 was observed when biochar was used as a soil amendment (4% by weight). Our results suggest that PCM can facilitate TNT and 2,4-dinitroanisole decay via a surface-promoted hydrolysis at neutral pH conditions, suggesting a promising alternative for in situ soil remediation.

Predicted detonation properties at the Chapman-Jouguet state for proposed energetic materials (MTO and MTO3N) from combined ReaxFF and quantum mechanics reactive dynamics

The development of new energetic materials (EMs) with improved detonation performance but low sensitivity and environmental impact is of considerable importance for applications in civilian and military fields. Often new designs are difficult to synthesize so predictions of performance in advance is most valuable. Examples include MTO (2,4,6-triamino-1,3,5-triazine-1,3,5-trioxide) and MTO3N (2,4,6-trinitro-1,3,5-triazine-1,3,5-trioxide) suggested by Klapötke as candidate EMs but not yet successfully synthesized. We propose and apply to these materials a new approach, RxMD(cQM), in which ReaxFF Reactive Molecular Dynamics (RxMD) is first used to predict the reaction products and thermochemical properties at the Chapman Jouguet (CJ) state for which the system is fully reacted and at chemical equilibrium. Quantum mechanics dynamics (QMD) is then applied to refine the pressure of the ReaxFF predicted CJ state to predict a more accurate final CJ point, leading to a very practical calculation that includes accurate long range vdW interactions needed for accurate pressure. For MTO, this RxMD(cQM) method predicts a detonation pressure of P_CJ = 40.5 GPa and a detonation velocity of D_CJ = 8.8 km s^-1, while for MTO3N it predicts P_CJ = 39.9 GPa and D_CJ = 8.4 km s^-1, making them comparable to HMX (P_CJ = 39.5 GPa, D_CJ = 9.1 km s^-1) and worth synthesizing. This first-principles-based RxMD(cQM) methodology provides an excellent compromise between computational cost and accuracy including the formation of clusters that burn too slowly, providing a practical mean of assessing detonation performances for novel candidate EMs. This RxMD(cQM) method that links first principles atomistic molecular dynamics simulations with macroscopic properties to promote in silico design of new EMs should also be of general applicability to materials synthesis and processing.

Facile preparation of rGO/MFe2O4(M = Cu, Co, Ni) nanohybrids and its catalytic performance during the thermal decomposition of ammonium perchlorate

Reduced graphene oxide/metal ferrite (rGO/MFe₂O₄, M = Cu, Co, Ni) nanohybrids are successfully prepared through a simple, one-step hydrothermal method. The rGO/MFe₂O₄ nanohybrids are characterized by XRD, TEM, FT-IR, XPS, Raman and BET surface area measurements. The rGO/MFe₂O₄ nanohybrids demonstrate amazing catalytic activities on the thermal decomposition of ammonium perchlorate (AP). DSC results indicate that rGO/MFe₂O₄ nanohybrids (3 wt%), could decrease the decomposition temperature of pure AP from 424.7 °C to 329.1 °C, 338.3 °C, and 364.8 °C, respectively. This enhanced catalytic performance is mainly attributed to the synergistic effect of NPs and rGO. The activation energy (E_a) of AP mixed with nanohybrids is investigated by two isoconversion methods, Flynne–Walle–Ozawa (FWO) and Kissinger–Akahira–Sunose (KAS), on a conversion degree (α) range from 0.05 to 0.95. The values of E_a calculated from the above two methods matched with each other. A strong dependence of E_a on α is observed, indicating a complex decomposition process.

The rGO/MFe₂O₄ (M = Cu, Co, Ni) nanohybrids show amazing catalytic activity in the thermal decomposition process of AP.

Synthesis and thermal behavior of a fused, tricyclic pyridine-based energetic material: 4-amino-5-nitro-[1,2,5]oxadiazolo[3,4-e]tetra-zolo[1,5-a]pyridine-3-oxide

Combination of nitro, amino, tetrazole, and furoxano with pyridine gave a novel fused, tricyclic energetic material with good detonation properties.

A novel cocrystal composed of CL-20 and an energetic ionic salt

A novel nitroamine/energetic ionic salt cocrystal explosive composed of CL-20 and 1-AMTN in a 1 : 1 molar ratio was discovered and characterized. It shows an appropriate explosive power and good mechanical sensitivity relative to RDX currently in use.

Self-assembled energetic 3D metal–organic framework [Na8(N5)8(H2O)3]n based on cyclo-N5–

A new 3D zeolite-like MOF [Na₈(N₅)₈(H₂O)₃]_n with an enhanced stability has been successfully synthesized by the self-assembly of Na⁺ with cyclo-N₅⁻ ligands.

Carbon-free energetic materials: computational study on nitro-substituted BN-cage molecules with high heat of detonation and stability

A new series of high-energy density materials (HEDMs) B₆N₆H_6−n(NO₂)_n (n = 1–6) are studied at the M06-2X/6-311++G**, ωB97XD/6-311++G** and B3LYP/6-311++G** levels. Analysis of the structural changes caused by substituting the NO₂ and the electronic structures, such as electron localization function (ELF), Wiberg bond index (WBI), charge transfer and bond dissociation energies (BDE), provide important insights into the essence of the chemical characteristics and stability. Moreover, the Born–Oppenheimer molecular dynamic (BOMD) simulation is performed to verify their stability, which suggests that only the BN-cage derivatives with one and two nitro groups bonding with boron atoms (NO₂-1-1 and NO₂-2-1) can remain stable under ambient conditions. To predict the detonation performance and sensitivity of these two stable BN-cage energetic molecules accurately, the density, gas phase enthalpy of formation, enthalpy of sublimation, detonation performance, impact sensitivity and BDE are calculated systematically. The calculation results show that both NO₂-1-1 and NO₂-2-1 have a higher heat of detonation, higher value of h₅₀, and larger BDE of trigger bonds than CL-20.

A new series of high-energy density materials were created by replacing the H atoms in the BN-cage with nitro groups.

Direct insight into the formation driving force, sensitivity and detonation performance of the observed CL-20-based energetic cocrystals

This work elucidated the underlying mechanism of the dramatic and divergent physicochemical properties of CL-20-based energetic cocrystals.

A highly stable and tightly packed 3D energetic coordination polymer assembled from nitrogen-rich tetrazole derivatives

A tightly packed 3D energetic cadmium(ii) coordination polymer was synthesized with high stability and remarkable energetic performance.

Dendritic Polynitrato Energetic Motifs: Development and Exploration of Physicochemical Behavior through Theoretical and Experimental Approach

Considering the fundamental and most desirable characteristics of energetic materials, a series of 1,2,3-triazole-based heterocyclic energetic motifs nicely tuned with nitrato (-ONO₂) functionality were synthesized by a microwave-assisted environmental friendly synthetic approach with good yields. Thermal stability and the nature of evolved gases on decomposition of structurally characterized energetic motifs were analyzed by thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) analysis and Fourier transform infrared coupled with TGA-DSC. The explosiveness of these motifs was explored by calculation of enthalpy of formation and density employing density functional theory, and the detonation performances (detonation pressure and velocity) were explored using EXPLO5_V6.03. All of these compounds were calculated to have better oxygen balance (-36 to -52%) as compared to that of trinitrotoluene (-74%). Most of the nitrate ester derivatives were found to exhibit low impact sensitivities, high densities, good thermal stabilities, and promising detonation properties, and PN ₃ was observed to be a superior candidate in terms of its energetic characteristics. Hence, the experimental and theoretical outcomes strongly reflect that the present approach of developing dendritic high energetic materials bearing green explosive characteristics might be a potential pathway for designing and synthesizing green explosives with desired characteristics.

A Heat-Resistant and Energetic Metal-Organic Framework Assembled by Chelating Ligand

Heat-resistant explosives with high performance and insensitivity to external stimulus or thermal are indispensable in both the military and civilian worlds especially when utilized under harsh conditions. We designed and synthesized a new heat-resistant three-dimensional chelating energetic metal-organic framework (CEMOF-1) by employing 4-amino-4H-1,2,4-triazole-3,5-diol (ATDO) as a ligand. Because of its chelating 3D structural feature, good oxygen balance (-29.58%), and high crystal density (2.234 g cm^-3), CEMOF-1 demonstrates high decomposition temperature (445 °C), insensitivity to stimulation, and excellent detonation velocity (10.05 km s^-1) and detonation pressure (49.36 GPa). The advantages of facile synthesis, thermal stability, and powerful explosive performance make CEMOF-1 as a promising candidate for heat-resistant explosives in future applications.

Detection and Quantification of Inorganic and Organic Anions in Natural, Potable, and Wastewaters in Northern New York Using Capillary Zone Electrophoresis and Indirect UV Detection

Capillary zone electrophoresis (CZE) is a sensitive and rapid technique used for determining traces of inorganic and organic anions in potable, natural, and wastewaters. Here, CZE with indirect UV-diode array detection (CZE-DAD) was employed with a background electrolyte system comprising of an Agilent Technologies proprietary basic anion buffer at pH 12.0 and a forensic anion detection method. The limits of detection (LOD) for this method ranged between 3 and 5 ppm and involved hydrodynamic injection of 50 mbar for 6 s with a negative polarity separation voltage of −30 kV at 30°C, a detection wavelength of 350 nm and indirect reference of 275 nm. Fourteen different anions were checked for in the water samples that were examined and included bromide, chloride, thiosulfate, nitrate, nitrite, sulfate, azide, carbonate, fluoride, arsenate, phosphate, acetate, lactate, and silicate. The water samples were collected from Northern New York towns and the Raquette River water system, the third longest river in New York State and the largest watershed of the central and western Adirondacks. The concentrations detected for these anions ranged from <5.0 ppm to 260 ppm.

Explosives in the Cage: Metal-Organic Frameworks for High-Energy Materials Sensing and Desensitization

An overview of the current status of coordination polymers and metal-organic frameworks (MOFs) pertaining to the field of energetic materials is provided. The explosive applications of MOFs are discussed from two aspects: one for detection of explosives, and the other for explosive desensitization. By virtue of their adjustable pore/cage sizes, high surface area, tunable functional sites, and rich host-guest chemistry, MOFs have emerged as promising candidates for both explosive sensing and desensitization. The challenges and perspectives in these two areas are thoroughly discussed, and the processing methods for practical applications are also discussed briefly.