High Energy Density Compounds Research Articles

Exploring the Correlation between Azido-Tetrazolo Tautomerizations and Isomer Structures: Electron Density of Bonding N Atoms and N-N Bond Polarity.

Azido-tetrazolo tautomerizations between azido N-heteroaromatic compounds and tetrazole-fused energetic materials can produce a new generation of high-energy density compounds. Density functional theory (DFT) computations are performed to explore the relationship between reaction barriers and electron densities of bonding N atoms, i.e., the terminal N1 and heterocyclic N2 atoms, for six reported tautomerizations. The results reveal four linear correlations between reverse reaction barriers (Gr) and the electron densities of N1 and N2 atoms in the product. N1 electron density (ρN1) and N-N bond polarity, as measured by the difference between the electron densities on the two N atoms (ΔρN = ρN1 - ρN2) in products, are inversely proportional to the reverse reaction barriers. They are also proportional to the energy barrier differences between the forward and reverse reactions (ΔG = Gf - Gr). Polar solvents, including DMSO, water, and acetone, can effectively increase the reverse reaction barriers (Gr) by improving the stability of products. This regularity is further confirmed by its application to four additional tautomerizations and can be used to screen out unfavorable azido-tetrazolo tautomerization reactions and increase the success rate of such synthesis.

Theoretical exploration of the stabilities and detonation parameters of nitro-substituted 1H-benzotriazole.

The nitro group was introduced into the nitrogen heterocycle of 1H-benzotriazole to design a total of 31 derivatives. To estimate the thermal stability of these derivatives, the heat of formation (HOF) is calculated based on the isodesmic reaction. The bond dissociation energy (BDE) was also predicted based on the homolytic reaction to further evaluate the dynamic stability. To evaluate the possibility of utilizing as high energy density compounds (HEDCs), the detonation parameters including the detonation pressure (P), detonation velocity (D), and explosive heat (Q) are predicted by taking advantage of the Kamlet-Jacobs empirical equation. To measure the sensitivity to impact, both the characteristic height (H50) and free space in crystal (∆V) are considered in this paper. Based on our calculations, D-series and E are found to be the candidates for HEDCs. The Gaussian 09 software package was used in this paper. The B3PW91 hybrid function with the 6-311 + G(d,p) basis set was chosen to perform the structural optimization, frequency analysis, heat of formation, and bond dissociation energy. The detonation parameters were calculated following the Kamlet-Jacobs equation.

Theoretical study about the thermal stability and detonation performance of the nitro-substituted derivatives of 4-(1H-1,2,4-triazol-1-yl) pyrimidine

The nitro groups are introduced into 4-(1H-1,2,4-triazol-1-yl) pyrimidine to substitute the hydrogen atoms successively, through which a total of 31 derivatives are constructed to look for high energy density compounds (HEDCs). To probe the thermal stabilities, the heats of formation (HOFs) are calculated by using the G3MP2 method. To explore the dynamic stability, the natural bond orbital (NBO) analysis is performed to confirm the trigger bond, for which the bond dissociation energy is calculated using the B3PW91 method with the 6-311 + G(d,p) basis set. Furthermore, the detonation velocity (D), the detonation pressure (P), the molecular density (ρ), the explosive heat (Q), and character height (H50) are also predicted. Based on our calculation, it is confirmed that D1, D2, D5, and E are potential high-energy-density compounds with sufficient stability and excellent detonation performance.

Detonation properties and sensitivities of a series of -NHNH-/-N = N- bridged tetrazole-based energetic materials

To obtain novel high-energy density compounds with superior detonation properties and sensitivity to those of RDX, a series of furazan/tetrazole/tetrazine-tetrazole-N = N-tetrazole-furazan/tetrazole/tetrazine and furazan/tetrazole/tetrazine-tetrazole-NHNH-tetrazole-furazan/tetrazole/tetrazine-based energetic materials were designed. Their structures were optimised by Gaussian software with density functional theory at B3LYP/6-311G (d,p) level. Based on the optimised structures, their frontier orbital energies, heats of formation and detonation properties were calculated. The results indicate that the compound with tetrazole-tetrazole-N = N-tetrazole-tetrazole parent structure and -N3 energetic group has the highest value of heat of formation while the compound with tetrazine-tetrazole-NHNH-tetrazole-tetrazine parent structure and -C(NO2)3 energetic group possess the highest values of detonation velocity and detonation pressure. Most of the designed compounds have higher values of h 50 than those of RDX (28 cm) and HMX (32 cm), and series E had higher average values of impact sensitivity. Finally, taking detonation properties and impact sensitivity into consideration, six compounds (A2, A8, C8, D2, F7 and F8) were selected as potential candidate materials for high-energy density materials, and their electronic and physicochemical properties were investigated.

The intramolecular integration of carbonyl and N-nitroamino groups to effectively balance the energy and sensitivity of N-nitroamino-functionalized bisazoles

In this study, employing an innovative method by introducing the N-nitroamino groups into bis(1,2,4-oxadiazoles) skeleton for the first time, a fine balance between high detonation properties and mechanical stability of N-nitroamino-functionalized bisazoles was achieved. A novel compound N,N'-(5,5′-dioxo-[3,3′-bi(1,2,4-oxadiazole)]-4,4′(5H,5′H)-diyl)dinitramide (3) was synthesized using straightforward three-step synthetic routes. Compound 3 not only has a high crystal density of 1.932 g cm−3 at 296 K, but also competes well in impact and friction sensitivities of 10 J and 160 N among all reported energetic N-nitroamine analogues. Meanwhile, the energy level (detonation velocity: VD = 9106 m s−1; detonation pressure: P = 36.6 GPa) of 3 is much superior to that of benchmark explosive 1,3,5-trinitro-1,3,5-triazacyclohexane (RDX, VD = 8801 m s−1; P = 33.6 GPa) and approaches 1,3,5,7-tetranitro-1,3,5,7-tetrazocane (HMX, VD = 9144 m s−1; P = 39.2 GPa). Additionally, with a striking high density of 1.929 g cm−3, hydroxylammonium salt 8 (VD = 9507 m s−1; P = 40.1 GPa) exhibits a prominent detonation performance comparable to the ε-2,4,6.8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (ε-CL-20, VD = 9455 m s−1; P = 46.7 GPa). This work may give new insight into improving the mechanical stability of energetic materials and is beneficial for developing novel high-energy–density compounds with excellent overall performance.

Theoretical Prediction on Properties of 3,4-Bisnitrofurazanfuroxan (DNTF) Crystal and its Polymer Bonded Explosives (PBXs) Through Molecular Dynamics (MD) Simulation

3,4-Bisnitrofurazanfuroxan (DNTF) is a typical high energy density compound (HEDC), it has high crystal density and detonation parameters, but also high mechanical sensitivity. To decrease its mechanical sensitivity, the DNTF based polymer bonded explosives (PBXs) was designed. The pure DNTF crystal and PBXs models were established. The stability, sensitivity, detonation performance and mechanical properties of DNTF crystal and PBXs models were predicted. Results show that PBXs models containing fluorine rubber (F2311) and fluorine resin (F2314) have higher binding energy, meaning that DNTF/F2311 and DNTF/F2314 is relatively more stable. PBXs models have higher value of cohesive energy density (CED) than pure DNTF crystal, DNTF/F2311 and DNTF/F2314 have the highest value of CED, implying that the sensitivity of PBXs is effectively decreased, DNTF/F2311 and DNTF/F2314 is more insensitive. PBXs have lower crystal density and detonation parameters than DNTF, the energy density is declined, DNTF/F2314 has higher energetic performance than other PBXs. Compared with pure DNTF crystal, engineering moduli (tensile modulus, shear modulus, bulk modulus) of PBXs models are obviously decreased, but Cauchy pressure is increased, implying that the mechanical properties of PBXs is superior to pure DNTF component, the PBXs containing F2311 or F2314 have more preferable mechanical properties. Consequently, DNTF/F2311 and DNTF/F2314 have the best comprehensive properties and is more attractive among the designed PBXs, indicating that F2311 and F2314 are more advantageous and promising in ameliorating properties of DNTF. The properties of DNTF crystal and PBXs models were predicted through molecular dynamics (MD) method under Materials Studio 7.0 package. The MD simulation was performed with isothermal-constant volume (NVT) ensemble, and the force field was chosen as COMPASS force field. The temperature was set as 295K, the time step was 1fs and the total MD simulation time was 2ns.

Design of derivatives of FOX-7-based new four-member heterocyclic insensitive high energy density molecules: a theoretical prospectives

Theoretical analysis of the novel, insensitive and high-energy density compounds based on the 1,1-dinitro-2,2-diamino-ethylene (FOX-7) moiety is presented here. In order to better serve as a prospective insensitive, high-energy molecule, a few novel heterocyclic four-member compounds were developed. The atoms in molecule (AIM) calculations have been used to estimate the stability of the C-NO2 bond as well as the covalent nature of the bonds. Using the Gaussian-16 quantum chemistry software, the electronic structure computations have been retrieved at the B3LYP level of theory with an aug-ccpVDZ basis set. It was discussed the impact sensitivity, thermal stability, detonation characteristics, harmonic vibrational frequency calculations, natural bond orbital calculations, the optimised structure of these molecules and more. The crystal density, activation energy for the nitro (C-NO2) to nitrito (C-ONO) transformation during the first stage of thermal breakdown, and the C-NO2 bond dissociation energy with BSSE correction of these molecules have been comprehensively investigated. These newly modelled compounds have been discovered to exhibit comparable detonation characteristics to those of FOX-7, which implies that they should be synthesised in a lab by experienced experimentalists.

Oxygen vacancies in Ru/TiO2 - drivers of low-temperature CO2 methanation assessed by multimodal operando spectroscopy

SummaryHydrogenation of CO2 is very attractive for transforming this greenhouse gas into valuable high energy density compounds. In this work, we developed a highly active and stable Ru/TiO2 catalyst for CO2 methanation prepared by a solgel method that revealed much higher activity in methanation of CO2 (ca. 4–14 times higher turnover frequencies at 140–210°C) than state-of-the-art Ru/TiO2 catalysts and a control sample prepared by wetness impregnation. This is attributed to a high concentration of O-vacancies, inherent to the solgel methodology, which play a dual role for 1) activation of CO2 and 2) transfer of electrons to interfacial Ru sites as evident from operando DRIFTS and in situ EPR investigations. These results suggest that charge transfer from O-vacancies to interfacial Ru sites and subsequent electron donation from filled metal d-orbitals to antibonding orbitals of adsorbed CO are decisive factors in boosting the CO2 methanation activity.

A theoretical library of N1s core binding energies of polynitrogen molecules and ions in the gas phase.

Polynitrogen molecules and ions are important building blocks of high energy density compounds (HEDCs). High energy bonds formed at the N sites can be effectively probed by X-ray photoelectron spectroscopy (XPS) at the N K-edge. In this work, with the density functional theory and the ΔKohn-Sham scheme, we simulated the N1s ionic potentials (IPs) of 72 common polynitrogen molecules [tetrazoles, pentazole (N5H), diazines, triazines, tetrazines, furazans, oxazoles and oxadiazoles], ions [pentazolate anion (cyclo-N5-), pentazenium cation (N5+), etc.], and molecular (NH3⋯N5H, H2O⋯N5H) and ionic (NH4+⋯N5-, H3O+⋯N5-) pairs, as well as mononitrogen relatives. These constitute a small theoretical database for absolute N1s IPs with an average accuracy of ca. 0.3 eV. To understand the structure-IP relationship within this family, effects of side substituent and bridging groups, local bonding types (amine or imine N), charge and protonation states, and vibronic coupling were analyzed based on selected systems. This study in the gas phase collects inherent chemical shifts of nitrogen in high-energy NN and NC bonds, which provides an essential reference into XPS interpretations of more complex HEDCs in the solid state. We especially highlight the evident N1s chemical shifts induced by protonation for nitrogen in the five-membered ring (N5H versus cyclo-N5-, ca. 7 eV; NH3⋯N5H versus NH4+⋯N5-, ca. 3 eV; H2O⋯N5H versus H3O+⋯N5-, ca. 2 eV), and suggest XPS as a sensitive tool in determining the hydrogen positions in pentanitrogen-based HEDCs.

Conception and optimization of an ammonia synthesis superstructure for energy storage

Ammonia has a potential as carbon-free and high-energy density compound for chemical storage of renewable energies and its synthesis from green H2 requires to be as energetically efficient as possible. In this work, a superstructure optimization methodology for process synthesis is proposed and applied to an ammonia production process. The approach covers three different scales: process, equipment, and molecules. Process scale refers to finding the optimal process structure, while the equipment scale is related to the best set of operating conditions, and the molecular scale studies two catalysts (Fe and Ru) with their respective kinetic rates. The optimization intends to minimize the Levelized Cost of Ammonia (LCOA) and maximize the energy efficiency. The best trade-off is found with the Ru catalyst, with an LCOA of 766€/tNH3 and 57.2% of energy efficiency. In comparison with reference cases, the LCOA decreases 0.6% and the energy efficiency increases 1.5%. The main improvement is found in the pressure, 75bar, reduced in 25%. The production of 11.6tNH3/day equals to 2.5MW of stored power from 3MW supplied as H2 to the process, with a total energy consumption of 10.67kWh/kgNH3, including prior H2 and N2 production processes.

Computational Design of High Energy RDX-Based Derivatives: Property Prediction, Intermolecular Interactions, and Decomposition Mechanisms.

A series of new high-energy insensitive compounds were designed based on 1,3,5-trinitro-1,3,5-triazinane (RDX) skeleton through incorporating -N(NO2)-CH2-N(NO2)-, -N(NH2)-, -N(NO2)-, and -O- linkages. Then, their electronic structures, heats of formation, detonation properties, and impact sensitivities were analyzed and predicted using DFT. The types of intermolecular interactions between their bimolecular assemble were analyzed. The thermal decomposition of one compound with excellent performance was studied through ab initio molecular dynamics simulations. All the designed compounds exhibit excellent detonation properties superior to 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), and lower impact sensitivity than CL-20. Thus, they may be viewed as promising candidates for high energy density compounds. Overall, our design strategy that the construction of bicyclic or cage compounds based on the RDX framework through incorporating the intermolecular linkages is very beneficial for developing novel energetic compounds with excellent detonation performance and low sensitivity.

Design and properties of a new family of wing-like and propeller-like multi-tetrazole molecules as potential high-energy density compounds.

Density functional theory (DFT) methods were employed to design a new family of wing-like and propeller-like multi-tetrazole molecules based on the combination of N-center multi-tetrazole and various energetic groups. The optimized geometry, electronic properties, and thermodynamics were calculated for investigating the molecular stability and chemical reactivity. Their energetic parameters including density, heats of formation, detonation properties, and impact sensitivity were extensively evaluated, and the effects of energetic groups were investigated as well. These newly designed wing-like and propeller-like multi-tetrazole molecules exhibit acceptable oxygen balance, moderate impact sensitivities, high density, excellent heats of formation, and good detonation performance. Especially, B3, B4, B5, and B6 are very helpful for enhancing their detonation performance (D ≥ 9500m·s-1, P ≥ 41 GPa) are promising candidates for new environmentally friendly HEDMs.

Chemical study of fused ring tetrazine derivatives as possible high energy density materials (HEDMs).

Using density functional theory (DFT), enthalpy of formation (HOF), thermodynamic properties, and detonation properties of a series of tetrazine fused ring derivatives are calculated. The results show that the introduction of coordinated oxygen is beneficial to increase the HOF value. The effects of different substituents on HOF are as follows: -C(NO2)3 > -N3 > -CH(NO2)2 > -NHNO2 > -NO2 > -NHNH2 > -H > -OH. Introduction of -H, -NH2, and -NHNH2 on the parent is not conducive to improving the detonation performance, while the introduction of -C(NO2)3 is conducive to improving the detonation performance of the designed compound. The explosion velocity of the newly designed compounds varies between 8.96 and 10.48km·s-1. The explosion pressure varies between 35.97 and 51.80 GPa, and the density varies between 1.83 and 2.00g·cm-3. Considering the thermal stability, density, and detonation properties, most of these compounds designed this time can be used as potential candidates for high energy density compounds.

Theoretical design on a series of new cage‐shaped high energy density compounds

AbstractA series of new cage compounds with high energy and low sensitivity by introducing –C(R2)–, –N(R)–, and –O– were designed. Then their properties including electronic structures, heats of formation, densities, detonation performances, thermal stability, and impact sensitivity were investigated using density functional theory. The results show that most of the designed compounds show excellent performance comparable with CL‐20, indicating that designing novel cage compounds is a very effective way to obtain potential energetic compounds with outstanding detonation properties. Taking both the detonation performance and stability into consideration, six compounds may be selected as attractive potential candidates of high energy density compounds. It may be expected that our results would contribute to the theoretical design of new‐generation energetic explosives.

Butterfly wing fans the fire: High efficient combustion of CWs/CL-20/AP nanocomposite for light ignited micro thruster using multi-channeled hierarchical porous structure from butterfly wing scales

To meet the requirement of miniaturization and integration of the micro thrusters based on the chemical fuels, high-energy density compound is an emerging material as the chemical fuel. However, it is still challenging to realize the high-efficiency, stable and self-sustaining microcombustion of the high-energy density chemical fuels. Herein, we report the high-performance microcombustion of CWs/AP/CL-20 composite with nanoscale 2,4,6,8,10,12-(hexanitrohexaaza)cyclododecane (CL-20) and oxidizer ammonium perchlorate (AP) confined in a self-standing carbonized butterfly wing scales (CWs) matrix. CWs with multi-channeled hierarchical porous structure provide a model architecture for loading of AP and CL-20. CL-20 is designed to serve as heat/pressure loss compensate agent due to its high-energy density, fast energy release rate and large amounts of gas release during combustion process. The combustion of CWs/AP/CL-20 is greatly enhanced due to the enhanced heat and mass transfer originating from the multi-channeled hierarchical porous structure and synergistic reactions between components at nanoscales, which is demonstrated as promising solid-propellant for the micro thruster. It is found that the sample with oxygen balance close to zero, which can be conveniently regulated by adjusting the mass ratio of CL-20 and AP, has the best microcombustion performance, resulting in a specific impulse of 383.5 N·s/kg.

New Potential High Energy Density Compounds: 7-Amino-6-nitro-[1,2,5]oxadiazolo[3,4-b]pyridine-1-oxide Derivatives

New Potential High Energy Density Compounds: 7-Amino-6-nitro-[1,2,5]oxadiazolo[3,4-b]pyridine-1-oxide Derivatives

Theoretical investigations on the density, detonation performance and stability of fluorinated hexanitroadamantanes

Cage compounds such as hexanitroadamantane (HNA) and hexanitrohexaazaisowurtzitane (HNIW, CL-20) constitute an important category of energetic compounds owing to the strained compact cage structure. Introduction of energetic substituents on the cage skeleton can further improve their energetic performance. In this paper, 24 substituted derivatives of fluorine-containing energetic groups of HNA are studied at the M06-2X/6-31G* level of density functional theory. The densities close to the experimental values are obtained by using the fitting equation. Based on the calculated densities and heats of formation, detonation properties are predicted using the modified Kamlet-Jacobs equations according to the largest exothermic principle. The contribution to detonation performance of various groups has the order of –C(NO2)2NF2 > –SF5 > –C(NO2)2F > –NF2 > –OCF3 > –CF3 > –F > –SCF3. As more fluorine-containing groups being introduced, detonation velocities and pressures increase quickly. Thermal stability has been discussed by the bond dissociation energies. The C-NO2 bond is the trigger bond of all the studied compounds. According to the energetics and stability criteria as a high energy density compound (HEDC), B2, B3, B7, C2, and C7 are the good candidates. The influences of the fluorine-containing groups found in this study will be beneficial to design of new fluorinated HEDCs by modifying structure.

Theoretical predictions on pentaerythritol tetranitrate‐based high energy density compounds

AbstractA novel family of pentaerythritol tetranitrate (PETN) derivatives based parent PETN skeleton were designed by introducing two energetic groups –NF2 and –NO2. Their electronic structure, heats of formation, detonation properties, impact sensitivity, and thermal stability were investigated by using density functional theory. The findings reveal that most of the title compounds have good detonation performance. The –NF2 group played an important role in improving the densities, heats of detonation, and detonation properties of the designed molecules. The values of h50 for almost all the PETN derivatives are higher than that of octahydro‐1,3,5,7‐tetranitro‐1,3,5,7‐tetrazocine. An analysis of bond dissociation energy suggests that the N‐NO2 bond tends to be a trigger bond in thermal decomposition. Taking both detonation properties and thermal stabilities into consideration, the three compounds may be selected as potential high‐energy‐density compounds.

Bis-3,5-Diamino-1,2,4-Triazolyl-1,2,4,5-Tetrazine: From Insensitive High Energy Density Materials to Small Molecule Organic Semiconductors

Besides the well-known pyrotechnic applications of insensitive high energy compounds such as s-tetrazine, they are promising materials for relevant applications (e.g., electrochemical energy storage, photocatalysis). Bis-3,5-diamino-1,2,4-triazolyl-1,2,4,5-tetrazine (BDTT) is a nitrogen-rich conjugated heterocyclic compound (nitrogen ≈ 71 wt %), inert to ignition and mechanical stimuli and thermally stable up to 370 °C. The solvent-free crystalline structure of this high energy density compound (named IEF-12 for IMDEA energy framework) is reported here for the first time using the high resolution powder X-ray diffraction (PXRD) and 1H, 13C, and 15N solid state nuclear magnetic resonance (NMR) spectroscopy. We demonstrate that IEF-12 has features of a small molecule organic semiconductor, namely, lamellar π-stacked crystal packing in the solid state, a low energy optical bandgap Egopt = 2.27 eV, and a relatively high value of dielectric constant εr = 4.86. Overall, we demonstrated on IEF-12 that insensitive high energy density materials (HEDM) may open an avenue for nonclassically structured organic semiconductors, paving the way for optoelectronic and photovoltaic applications.

Computer-aided design and property prediction of novel insensitive high-energy heterocycle-substituted derivatives of cage NNNAHP

A series of new derivatives of cage 2,4,6,8,10,12,13,14,15-nanonitro-2,4,6,8,10,12,13,14, 15-nanoazaheptacyclo[5.5.1.13,11,15,9] pentadecane (NNNAHP) were designed by incorporating combination of heterocyclic and non-heterocyclic substituents and studied by using density functional theory. The results indicate that the -tetrazine and -N(NO2)2 are very beneficial structural fragments to increase their heat of formation. The introduction of different heterocyclic and non-heterocyclic groups can produce different effects on different properties: large densities (1.88-2.06gcm-3), high detonation velocities (8.17-9.83kms-1), excellent detonation pressures (30.55-46.02GPa), and outstanding heat of detonations (1169.80-1637.19calg-1). The analysis of bond dissociation energy values show that the N(cage)-NO2 is the weakest bond, and it may turn into a trigger bond during detonation. Almost all the derivatives are thermally more stable than the parent compound. All the substituted derivatives are insensitive as compared with the parent compound. According to excellent detonation properties, high thermal stability, and good insensitivity, 10 compounds may be chosen as potential high-energy density compounds.