Improved corrosion resistance and thermal stability of insensitive NTO explosives by MXene modification in the presence of non-covalent bonds

Strong corrosiveness to metals is the main factor restricting the widespread application of the insensitive explosive 3-nitro-1,2,4-triazole-5-one (NTO).

CL-20-Based Cocrystal Energetic Materials: Simulation, Preparation and Performance

The cocrystallization of high-energy explosives has attracted great interests since it can alleviate to a certain extent the power-safety contradiction. 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaaza-isowurtzitane (CL-20), one of the most powerful explosives, has attracted much attention for researchers worldwide. However, the disadvantage of CL-20 has increased sensitivity to mechanical stimuli and cocrystallization of CL-20 with other compounds may provide a way to decrease its sensitivity. The intermolecular interaction of five types of CL-20-based cocrystal (CL-20/TNT, CL-20/HMX, CL-20/FOX-7, CL-20/TKX-50 and CL-20/DNB) by using molecular dynamic simulation was reviewed. The preparation methods and thermal decomposition properties of CL-20-based cocrystal are emphatically analyzed. Special emphasis is focused on the improved mechanical performances of CL-20-based cocrystal, which are compared with those of CL-20. The existing problems and challenges for the future work on CL-20-based cocrystal are discussed.

Theoretical Study on CL-20-Based Cocrystal Energetic Compounds in an External Electric Field

An external electric field has great effects on the sensitivity of cocrystal energetic materials. In order to find out the relationship between the external electric field and sensitivity of cocrystals 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane/benzotrifuroxan (CL-20/BTF), 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane/3,4-dinitropyrazole (CL-20/DNP), and 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane/1-methyl-3,5-dinitro-1,2,4-triazole (CL-20/MDNT), density functional theory at B3LYP-D3/6-311+G(d,p) and M062X-D3/ma-def2 TZVPP levels was employed to calculate frontier molecular orbitals, atoms in molecules (AIM) electron density values, bond dissociation energies (BDEs) of the N-NO2 bond, impact sensitivity (H 50), electrostatic potentials (ESPs), and nitro group charges (Q NO2 ) in this work. The results show that a smaller highest occupied molecular orbital-lowest unoccupied molecular orbital gap and the BDEs, as well as H 50, tend to have a larger sensitivity along with the positive directions in the external electric field. Moreover, a smaller local positive ESP (V s max) leads to better stability in the negative electric field. The sensitivity of cocrystal molecules decreases gradually in the negative external electric field with the increase of negative nitro group charges. Finally, the change in the bond lengths, AIM electron density values, and nitro group charges correlate well with the external electric field strengths.

Comparative investigation on the thermostability, sensitivity, and mechanical performance of RDX/HMX energetic cocrystal and its mixture

Molecular mechanics (MM) and molecular dynamics (MD) simulation method were applied to explore the impact of temperature (220-380 K) on the thermostability, sensitivity, and mechanical performance of RDX (1,3,5-trinitro-1,3,5-triazacyco-hexane)/HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane) energetic cocrystal and mixture models. The mechanical property, the maximum trigger bond length ([Formula: see text]), binding energy, and cohesive energy density (CED) of the pure RDX, β-HMX crystal, the cocrystal, and mixture models were acquired and compared. The results manifest that temperature has an important impact on the binding capacity between the components of the cocrystal and mixture. The binding energies decrease as the temperature rises, and the cocrystal has larger values than those of mixture. For all the models, the [Formula: see text] increases and the CEDs decrease with the rising temperature, implying that the sensitivity of the explosives increases, while the [Formula: see text] values of the cocrystal are smaller than those of HMX and the CED values are between those of RDX and β-HMX, indicating that the sensitivity has been enhanced through co-crystallization. As the temperature increases, the shear modulus (G), bulk modulus (K), and tensile modulus (E) values of all models have an evident downtrend. Simultaneously, G, K, and E values of the cocrystal model are less than those of RDX and β-HMX, while the K/G ratio and Cauchy pressure (C₁₂-C₄₄) are larger, signifying that co-crystallization can weaken the brittleness and enhance the ductility of the pure crystals. Compared with the mixture, the cocrystal has better ductility and stability.

Strategies for Achieving Balance between Detonation Performance and Crystal Stability of High-Energy-Density Materials

Performance-stability contradiction of high-energy-density materials (HEDMs) is a long-standing puzzle in the field of chemistry and material science. Bridging the gap that exists between detonation performance of new HEDMs and their stability remains a formidable challenge. Achieving optimal balance between the two contradictory factors is of a significant demand for deep-well oil and gas drilling, space exploration, and other civil and defense applications. Herein, supercomputers and latest quantitative computational strategies were employed and high-throughput quantum calculations were conducted for 67 reported HEDMs. Based on statistical analysis of large amounts of physico-chemical data, in-crystal interspecies interactions were identified to be the one that provokes the performance-stability contradiction of HEDMs. To design new HEDMs with both good detonation performance and high stability, the proposed systematic and comprehensive strategies must be satisfied, which could promote the development of crystal engineering of HEDMs to an era of theory-guided rational design of materials.

Theoretical studies on the structure and properties of DAT/BTNAT cocrystal under high pressure

The structural, electronic, and absorption properties of 3,5-diamino-1H-1,2,4-triazole (DAT) and 5,5′-bis(trinitromethyl)-3,3′-azo-1H-1,2,4-triazole (BTNAT) cocrystal under hydrostatic compression of 0–100 GPa were investigated by using periodic density functional theory with dispersion correction (DFT-D). The results indicate that a structural transformation occurred at 25 GPa. The structural transformation makes the positions of the molecules rearrange in the cocrystal and improves the stability and planarity. An analysis of the band gap and density of states indicates that the DAT/BTNAT cocrystal becomes more sensitive under compression. The absorption spectra illustrate that the DAT/BTNAT cocrystal has relatively high optical activity with the increasing pressure. Our work may offer some valuable information for understanding the behavior of energetic cocrystals under high pressure.

Modulating energetic performance through decorating nitrogen-rich ligands in high-energy MOFs

In the presence of different nitrogen-rich ligands, two energetic MOFs with formulas [Ag(tza)]_n (1) and [Ag(atza)]_n (2) (Htza = tetrazole-1-acetic acid and Hatza = (5-amino-1H-tetrazole-1-yl) acetic acid) were successfully synthesized and characterized. X-ray single crystal structure analysis shows that both 1 and 2 have 2D layer-like topologies. The experimental and theoretical evaluations reveal the promising properties of both energetic compounds, such as prominent heats of detonation, high thermal stabilities, good sensitivities and excellent detonation performances. In contrast to 1, interestingly, the introduction of the amino group in 2 leads to various coordination modes of the ligands and different stacking patterns of the frameworks, resulting in the observation of the shorter Ag-O, Ag-Ag, C-N, N-N, and N[double bond, length as m-dash]N bond lengths in 2. Consequently, 2 features superior heats of detonation and thermostability compared to 1. The nonisothermal thermokinetic parameters are obtained by using the Kissinger and Ozawa methods, while the standard molar enthalpies of formation are calculated from the determination of constant volume combustion energies. In addition, both compounds were explored as practical additives to promote the thermal decomposition of ammonium perchlorate (AP). This work may provide an effective approach for manipulating the energetic properties and thermostability of high-energy compounds via the perturbation of energetic groups.

Theoretical calculation into the effect of molar ratio on the structures, stability, mechanical properties and detonation performance of 1,3,5,7-tetranitro-1,3,5,7-tetrazocane/ 1,3,5-trinitro-1,3,5-triazacyco-hexane cocrystal

Molecular dynamics (MD) simulation was conducted to research the effect of molar ratio on the thermal stability, mechanical properties, and detonation performance of HMX (1,3,5,7-tetranitro-1,3,5,7-tetrazocane)/RDX (1,3,5-trinitro-1,3,5-triazacyco-hexane) cocrystal explosive at ambient condition. The binding energy, mechanical properties, and the detonation parameters of the pure β-HMX, RDX crystal, and the cocrystal models were got and contrasted. The results demonstrate that molar ratio has a great influence on the properties of the cocrystal system. The binding energy of the cocrystals has the maximum values at the 1:1 molar ratio, indicating that the stability of HMX/RDX(1:1) cocrystal is the best and HMX and RDX may prefer to cocrystallizing at 1:1 molar ratio. What's more, the tensile modulus (E) and shear modulus (G) of the HMX/RDX(1:1) cocrystals have the minimum value, while the C₁₂-C₄₄ and K/G have the maximum value, implying that the cocrystal at 1:1 molar ratio has the best mechanical properties. Simultaneously, the E, K, and G of the cocrystals are all smaller than those of β-HMX's and generally larger than those RDX's, while the Cauchy pressure (C₁₂-C₄₄) and K/G ratio were greater, demonstrating that cocrystallizing can improve the brittleness and enhance the ductility. The detonation velocity (D) and detonation pressure (P) decrease with the rising RDX content, while the properties are still superior to the pure RDX crystal; thus, the energy properties of the cocrystal are still excellent. In a word, HMX/RDX cocrystal at 1:1 molar ratio has the best thermal stability, mechanical properties, and the excellent energetic performance.

Novel strategies for synthesizing energetic materials based on BTO with improved performances

The layer-by-layer assembly of molecules is ubiquitous in nature. Highly ordered structures formed in this manner often exhibit fascinating material properties. A layer hydrogen bonding pairing approach allows the development of tunable energetic materials with targeted properties. A series of unusual energetic compounds based on 1H,1'H-5,5'-bistetrazole-1,1'-diolate (1), such as the salts of 3-amino-1,2,4-triazolium (2), aminoguanidinium (3), and hydrazinium (4), and the cocrystals of 4-amino-1H-pyrazole (5), 2-methylimidazole (6), and imidazole (7), were synthesized using this strategy. The structures of the obtained products 2-7 were fully characterized by elemental analysis, IR spectroscopy, ¹H NMR and ¹³C NMR spectroscopy, and single-crystal X-ray analysis. Their thermal decomposition behavior was studied by differential scanning calorimetry and thermogravimetry. Their mechanical sensitivities and detonation performances were also analyzed in detail. Results show that products 2-7 exhibit higher density, better detonation performances, and more excellent sensitivities than those of the same species of cation salts previously reported.

Theoretical investigations on structures, stability, energetic performance, sensitivity, and mechanical properties of CL-20/TNT/HMX cocrystal explosives by molecular dynamics simulation

In this article, the CL-20, TNT, HMX, CL-20/TNT, CL-20/HMX and different CL-20/TNT/HMX cocrystal models were established. Molecular dynamics method was selected to optimize the structures, predict the stability, sensitivity, energetic performance, and mechanical properties of cocrystal models. The binding energy, trigger bond length, trigger bond energy, cohesive energy density, detonation parameters, and mechanical properties of each crystal model were obtained. The influences of co-crystallization and molar ratios on performances of cocrystal explosives were investigated and evaluated. The results show that the CL-20/TNT/HMX cocrystal explosive with a molar ratio of 3:1:2 or 3:1:3 had larger binding energy and better stability, i.e., CL-20/TNT/HMX cocrystal explosive was more likely to be formed with these molar ratios. The cocrystal explosive had shorter maximal trigger bond length, but larger trigger bond energy and cohesive energy density than CL-20, namely, the cocrystal explosive had lower mechanical sensitivity and better safety than CL-20 and the safety of cocrystal model was effectively improved. The cocrystal model with a molar ratio of 3:1:2 had the best safety. The energetic performance of the cocrystal explosive with a molar ratio of 3:1:1, 3:1:2, or 3:1:3 was the best. These CL-20/TNT/HMX cocrystal models exhibited better and more desirable mechanical properties. In a word, the cocrystal model with molar ratio of 3:1:2 exhibited the most superior properties and was a novel and potential high-energy-density compound. This paper could provide practical helpful guidance and theoretical support to better understand co-crystallization mechanisms and design novel energetic cocrystal explosives.

Periodic DFT study of structural transformations of cocrystal NTO/TZTN under high pressure

Density functional theory (DFT) periodic calculations were performed to study the geometrical and electronic structures of energetic cocrystal NTO/TZTN under pressures ranging from 0 to 80 GPa. The optimized crystal structure by the GGA/PW91 (Perdew-Wang-91) and dispersion corrections corresponds well with the experimental values under ambient pressure. With the pressure increasing, the lattice constants, unit cell volumes, interatomic distances, H-bond energies, atomic charges, and bond populations of cocrystal NTO/TZTN change gradually. At pressures of 4, 8, and 23 GPa, three structural transformations occurred, shown by the results. The cyclization plays an important role in stabilizing the systems. The increasing pressure contributes to the increase of interaction force gradually. At 4 GPa, a new hydrogen bond O3⋯H5 is formed. At 8 GPa, the formation of eight membered rings is because of the existence of a covalent bond O1-H3 between two NTO molecules. In addition, a covalent interaction is formed between N2 and H4 atoms with the biggest H-bond energy compared to the others. As the pressure reaches 23 GPa, another new hydrogen bond forms between N8 and H5 atoms, which contributes to the formation of a five membered ring between NTO and TZTN. The electrons can move freely according to the results of the density of states between the valence and conduction bands when the pressure is high. This work will provide useful information in understanding the high-pressure effect on the structural transformation.

High-density HNIW/TNT cocrystal synthesized using a green chemical method

The main challenge for achieving better energetic materials is to increase their density. In this paper, cocrystals of HNIW (2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane, often referred to as CL-20) with TNT (2,4,6-trinitrotoluene) were synthesized using ethanol in a green chemical method. The cocrystal was formulated as C13H11N15O18 and possesses a higher density (1.934 g cm-3) than published previously (1.846 g cm-3). This high-density cocrystal possesses a new structure, which can be substantiated by the different types of hydrogen bonds. The predominant driving forces that connect HNIW with TNT in the new cocrystal were studied at ambient conditions using single-crystal X-ray diffraction, powder X-ray diffraction, Fourier transform-infrared spectroscopy and Raman spectroscopy. The results reveal that the structure of the new HNIW/TNT cocrystals consists of three one-dimensional hydrogen-bonded chains exploiting the familiar HNIW-TNT multi-component supramolecular structure, in which two hydrogen-bonded chains are between -NO2 (HNIW) and -CH (TNT), and one hydrogen-bonded chain is between -CH (HNIW) and -NO2 (TNT). The changes to the electron binding energy and type of element in the new cocrystal were traced using X-ray photoelectron spectroscopy. Meanwhile, the physicochemical characteristics alter after cocrystallization due to the hydrogen bonding. It was found that the new HNIW/TNT cocrystal is more thermodynamically stable than HNIW. Thermodynamic aspects of new cocrystal decomposition are investigated in order to explain this observation. The detonation velocity of new HNIW/TNT cocrystals is 8631 m s-1, close to that of HNIW, whereas the mechanical sensitivity is lower than HNIW.

Theoretical investigations on the structures and properties of CL-20/TNT cocrystal and its defective models by molecular dynamics simulation

"Perfect" and defective models of CL-20/TNT cocrystal explosive were established. Molecular dynamics methods were introduced to determine the structures and predict the comprehensive performances, including stabilities, sensitivity, energy density and mechanical properties, of the different models. The influences of crystal defects on the properties of these explosives were investigated and evaluated. The results show that, compared with the "perfect" model, the rigidity and toughness of defective models are decreased, while the ductility, tenacity and plastic properties are enhanced. The binding energies, interaction energy of the trigger bond, and the cohesive energy density of defective crystals declined, thus implying that stabilities are weakened, the explosive molecule is activated, trigger bond strength is diminished and safety is worsened. Detonation performance showed that, owing to the influence of crystal defects, the density is lessened, detonation pressure and detonation velocity are also declined, i.e., the power of defective explosive is decreased. In a word, the crystal defects may have a favorable effect on the mechanical properties, but have a disadvantageous influence on sensitivity, stability and energy density of CL-20/TNT cocrystal explosive. The results could provide theoretical guidance and practical instructions to estimate the properties of defective crystal models.

Theoretical investigation of the structures and properties of CL-20/DNB cocrystal and associated PBXs by molecular dynamics simulation

In this work, a CL-20/DNB cocrystal explosive model was established and six different kinds of fluoropolymers, i.e., PVDF, PCTFE, F₂₃₁₁, F₂₃₁₂, F₂₃₁₃ and F₂₃₁₄ were added into the (1 0 0), (0 1 0), (0 0 1) crystal orientations to obtain the corresponding polymer bonded explosives (PBXs). The influence of fluoropolymers on PBX properties (energetic property, stability and mechanical properties) was investigated and evaluated using molecular dynamics (MD) methods. The results reveal a decrease in engineering moduli, an increase in Cauchy pressure (i.e., rigidity and stiffness is lessened), and an increase in plastic properties and ductility, thus indicating that the fluoropolymers have a beneficial influence on the mechanical properties of PBXs. Of all the PBXs models tested, the mechanical properties of CL-20/DNB/F₂₃₁₁ were the best. Binding energies show that CL-20/DNB/F₂₃₁₁ has the highest intermolecular interaction energy and best compatibility and stability. Therefore, F₂₃₁₁ is the most suitable fluoropolymer for PBXs. The mechanical properties and binding energies of the three crystal orientations vary in the order (0 1 0) > (0 0 1) > (1 0 0), i.e., the mechanical properties of the (0 1 0) crystal orientation are best, and this is the most stable crystal orientation. Detonation performance results show that the density and detonation parameters of PBXs are lower than those of the pure CL-20 and CL-20/DNB cocrystal explosive. The power and energetic performance of PBXs are thus weakened; however, these PBXs still have excellent detonation performance and are very promising. The results and conclusions provide some helpful guidance and novel instructions for the design and manufacture of PBXs.

From intermolecular interactions to structures and properties of a novel cocrystal explosive: a first-principles study

By employing a first-principles method, we conducted a thorough study on a novel cocrystal explosive 1 : 1 NTO : TZTN and gained insight into the interaction-structure-property interrelationship. Mulliken bond orders, Hirshfeld surfaces, intermolecular binding energies, packing coefficients, and oxygen balance were calculated to analyze the intermolecular interactions and structures of the cocrystal explosive. The cocrystallization of NTO and TZTN molecules enhances the intermolecular binding force, which drives the synthesis of the cocrystal. However, the cocrystallization decreases the molecular packing density along the closest packed directions, which reduces the density by 10.5% and deteriorates the oxygen balance. All of these lead to a reduction in the detonation performance compared to NTO explosives. We have also proposed a new method to evaluate the impact sensitivity according to the lattice dynamics calculation. The cocrystal explosive has a lower impact sensitivity than TZTN but higher than NTO, which agrees well with experiments.

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.

Preparation of CL-20/DNDAP cocrystals by a rapid and continuous spray drying method: an alternative to cocrystal formation

A CL-20/DNDAP cocrystal explosive prepared by a spray drying method exhibited a small particle size with a narrow size distribution and good comprehensive performance.

Novel insensitive energetic-cocrystal-based BTO with good comprehensive properties

Combining a layer construction strategy with cocrystallization techniques, we designed and prepared a structurally unusual 1H,1′H-5,5′-bistetrazole-1,1′-diolate (BTO) based energetic cocrystal, which we also confirmed by single-crystal X-ray diffraction and powder-crystal X-ray diffraction. The obtained cocrystal crystallizes in a triclinic system, P-1 space group, with a density of 1.72 g cm⁻³. The properties including the thermal stability, sensitivity and detonation performance of the cocrystal were analyzed in detail. In addition, the thermal decomposition behavior of the cocrystal was studied by differential calorimetry and thermogravimetry tandem infrared spectroscopy. The results indicated that the cocrystal exhibits strong resistance to thermal decomposition up to 535.6 K. The cocrystal also demonstrates a sensitivity of >50 J. Moreover, its formation enthalpy was estimated to be 2312.0 kJ mol⁻¹, whereas its detonation velocity and detonation pressure were predicted to be 8.213 km s⁻¹ and 29.1 GPa, respectively, by applying K–J equations. Therefore, as expected, the obtained cocrystal shows a good comprehensive performance, which proves that a high degree of layer-by-layer stacking is essential for the structural density, thermal stability and sensitivity.

Combining a layer construction strategy with cocrystallization techniques, we designed and prepared an unusual energetic cocrystal, which confirmed by single-crystal X-ray diffraction.

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.

Molecular dynamics calculation on structures, stabilities, mechanical properties, and energy density of CL-20/FOX-7 cocrystal explosives

In this article, different CL-20/FOX-7 cocrystal models were established by the substitution method based on the molar ratios of CL-20:FOX-7. The structures and comprehensive properties, including mechanical properties, stabilities, and energy density, of different cocrystal models were obtained and compared with each other. The main aim was to estimate the influence of molar ratios on properties of cocrystal explosives. The molecular dynamics (MD) simulation results show that the cocrystal model with molar ratio 1:1 has the best mechanical properties and highest binding energy, so the CL-20/FOX-7 cocrystal model is more likely to form in 1:1 M ratio. The detonation parameters show that the cocrystal explosive exhibited preferable energy density and excellent detonation performance. In a word, the 1:1 cocrystal model has the best comprehensive properties, is very promising, and worth more theoretical investigations and experimental tests. This paper gives some original theories to better understand the cocrystal mechanism and provides some helpful guidance and useful instructions to help design CL-20 cocrystal explosives.

Theoretical investigation of the effects of the molar ratio and solvent on the formation of the pyrazole-nitroamine cocrystal explosive 3,4-dinitropyrazole (DNP)/2,4,6,8,10,12-hexanitrohexaazaisowurtzitane (CL-20)

The effects of the molar ratio, temperature, and solvent on the formation of the cocrystal explosive DNP/CL-20 were investigated using molecular dynamics (MD) simulation. The cocrystal structure was predicted through Monte Carlo (MC) simulation and using first-principles methods. The results showed that the DNP/CL-20 cocrystal might be more stable in the molar ratio 1:1 near to 318 K, and the most probable cocrystal crystallizes in the triclinic crystal system with the space group P[Formula: see text]. Cocrystallization was more likely to occur in methanol and ethanol at 308 K as a result of solvent effects. The optimized structure and the reduced density gradient (RDG) of the DNP/CL-20 complex confirmed that the main driving forces for cocrystallization were a series of hydrogen bonds and van der Waals forces. Analyses of the trigger bonds, the charges on the nitro groups, the electrostatic surface potential (ESP), and the free space per molecule in the cocrystal lattice were carried out to further explore their influences on the sensitivity of CL-20. The results indicated that the DNP/CL-20 complex tended to be more stable and insensitive than pure CL-20. Moreover, an investigation of the detonation performance of the DNP/CL-20 cocrystal indicated that it possesses high power. Graphical abstract DNP/CL-20 cocrystal models with different molar ratios were investigated at different temperatures using molecular dynamics (MD) simulation methods. Binding energies and mechanical properties were probed to determine the stability and performance of each cocrystal model. Solvated DNP/CL-20 models were established by adding solvent molecules to the cocrystal surface. The binding energies of the models in various solvents were calculated in order to identify the most suitable solvent and temperature for preparing the cocrystal explosive DNP/CL-20.

Comparative studies on structures, mechanical properties, sensitivity, stabilities and detonation performance of CL-20/TNT cocrystal and composite explosives by molecular dynamics simulation

To investigate and compare the differences of structures and properties of CL-20/TNT cocrystal and composite explosives, the CL-20/TNT cocrystal and composite models were established. Molecular dynamics simulations were performed to investigate the structures, mechanical properties, sensitivity, stabilities and detonation performance of cocrystal and composite models with COMPASS force field in NPT ensemble. The lattice parameters, mechanical properties, binding energies, interaction energy of trigger bond, cohesive energy density and detonation parameters were determined and compared. The results show that, compared with pure CL-20, the rigidity and stiffness of cocrystal and composite models decreased, while plastic properties and ductility increased, so mechanical properties can be effectively improved by adding TNT into CL-20 and the cocrystal model has better mechanical properties. The interaction energy of the trigger bond and the cohesive energy density is in the order of CL-20/TNT cocrystal > CL-20/TNT composite > pure CL-20, i.e., cocrystal model is less sensitive than CL-20 and the composite model, and has the best safety parameters. Binding energies show that the cocrystal model has higher intermolecular interaction energy values than the composite model, thus illustrating the better stability of the cocrystal model. Detonation parameters vary as CL-20 > cocrystal > composite, namely, the energy density and power of cocrystal and composite model are weakened; however, the CL-20/TNT cocrystal explosive still has desirable energy density and detonation performance. This results presented in this paper help offer some helpful guidance to better understand the mechanism of CL-20/TNT cocrystal explosives and provide some theoretical assistance for cocrystal explosive design.

Theoretical insights into the effects of molar ratios on stabilities, mechanical properties, and detonation performance of CL-20/HMX cocrystal explosives by molecular dynamics simulation

To research and estimate the effects of molar ratios on structures, stabilities, mechanical properties, and detonation properties of CL-20/HMX cocrystal explosive, the CL-20/HMX cocrystal explosive models with different molar ratios were established in Materials Studio (MS). The crystal parameters, structures, stabilities, mechanical properties, and some detonation parameters of different cocrystal explosives were obtained and compared. The molecular dynamics (MD) simulation results illustrate that the molar ratios of CL-20/HMX have a direct influence on the comprehensive performance of cocrystal explosive. The hardness and rigidity of the 1:1 cocrystal explosive was the poorest, while the plastic property and ductibility were the best, thus implying that the explosive has the best mechanical properties. Besides, it has the highest binding energy, so the stability and compatibility is the best. The cocrystal explosive has better detonation performance than HMX. In a word, the 1:1 cocrystal explosive is worth more attention and further research. This paper could offer some theoretical instructions and technological support, which could help in the design of the CL-20 cocrystal explosive.

Theoretical insight into the sensitive mechanism of multilayer-shaped cocrystal explosives: compression and slide

Multilayer-shaped compression and slide models were employed to investigate the complex sensitive mechanisms of cocrystal explosives in response to external mechanical stimuli. Here, density functional theory (DFT) calculations implementing the generalized gradient approximation (GGA) of Perdew-Burke-Ernzerhof (PBE) with the Tkatchenko-Scheffler (TS) dispersion correction were applied to a series of cocrystal explosives: diacetone diperoxide (DADP)/1,3,5-trichloro-2,4,6-trinitrobenzene (TCTNB), DADP/1,3,5-tribromo-2,4,6-trinitrobenzene (TBTNB) and DADP/1,3,5-triiodo-2,4,6-trinitrobenzene (TITNB). The results show that the GGA-PBE-TS method is suitable for calculating these cocrystal systems. Compression and slide models illustrate well the sensitive mechanism of layer-shaped cocrystals of DADP/TCTNB and DADP/TITNB, in accordance with the results from electrostatic potentials and free space per molecule in cocrystal lattice analyses. DADP/TCTNB and DADP/TBTNB prefer sliding along a diagonal direction on the a-c face and generating strong intermolecular repulsions, compared to DADP/TITNB, which slides parallel to the b-c face. The impact sensitivity of DADP/TBTNB is predicted to be the same as that of DADP/TCTNB, and the impact sensitivity of DADP/TBTNB may be slightly more insensitive than that of DADP and much more sensitive than that of TBTNB.

Synthesis, crystal structure and properties of a new 1D polymeric nitrogen-rich energetic complex {TAG[Li(BTO)(H2O)]}n based on 1H,1′H-5,5′-bitetrazole-1,1′-diolate

The novel polymer {TAG[Li(BTO)(H₂O)]}_n, based on 1H,1′H-5,5′-bitetrazole-1,1′-diolate, opened up a new field on BTO-based energetic materials and anionic metal–organic frameworks.

Correlating the melting point alteration with the supramolecular structure in aripiprazole drug cocrystals

Structural reasons for the melting point variations in isostructural cocrystals of the aripiprazole drug are investigated through combined spectroscopic and diffraction studies.