CL-20 Crystals Research Articles

Constructing Porous Energetic Spherulites via Solvation-Growth Coupling for Enhanced Combustion.

The fabrication of materials with hierarchical structures has garnered great interest, owing to the potential for significantly enhancing their functions. Herein, a strategy of coupling molecular solvation and crystal growth is presented to fabricate porous spherulites of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), an important energetic material. With the addition of polyvinylpyrrolidone in the antisolvent crystallization, the metastable solvate of CL-20 is formed and grows spherulitically, and spontaneously desolvates to obtain the porous spherulite when filtration, in which the characteristic peak of the nitro group of CL-20 shifts detected by the in situ micro-confocal Raman spectroscopy. The effect of polyvinylpyrrolidone is thought to induce the solvation of CL-20, confirmed by density functional theory calculations, meanwhile acting on the (020) face of CL-20 to trigger spherulitic growth, demonstrated through infrared spectroscopy and Rietveld refinement of powder X-ray diffraction. Moreover, compared to common CL-20 crystals, porous spherulites exhibit enhanced combustion with increases of 6.24% in peak pressure, 40.21% in pressurization rate, and 9.63% in pressure duration effect, indicating the capability of hierarchical structures to boost the energy release of energetic crystals. This work demonstrates a new route via solvation-growth coupling to construct hierarchical structures for organic crystals and provides insight into the structure-property relations for material design.

Design a cross-linked film based on cellulose nanocrystals doping for enhancing the interfacial performance and desensitization of CL-20

Despite the extensive researches on CL-20 crystals, the mechanical safety issues and process problems of CL-20 applications have not been studied in-depth. Herein, the cellulose nanocrystals (CNC) was doped in microcrystalline wax (MW), oxidized microcrystalline wax (OMW) and hydrogel (PPC) to design and fabricate the cross-linked CL-20 composites by simple water-suspension melting and freeze-drying methods. The composites were characterized by SEM, XPS, TG-DSC, XRD, mechanical sensitivity device and inclined chute tester. It is found that the CNC@OMW composite film exhibits excellent coating effect (99.96%) on CL-20 due to the cross-linking results. The Ea of CL-20 is increased from 190.92 to 388.71 kJ/mol under the synergistic effect of the excellent compatibility between components and the compact coating structure of CNC@OMW. Additionally, the film enhances the Tp0 of CL-20 from 218.15 to 222.66 ℃ and Tb from 220.27 to 223.73 ℃, respectively. While, the PPC@CNC only promoted Ea, Tp0 and Tb of CL-20–292.89.71 kJ/mol, 224.22 ℃ and 225.66 ℃, respectively. Besides, the XRD results confirms that three composite films dose not cause a transformation of the ε-CL-20 crystal phase. Most importantly, the cross-linked film brings mechanical sensitivity of CL-20 from 60 N and 3.5 J to a level of over 360 N and 10.4 J, comparable to WO3/Al nanothermite with 5 wt% polyaniline (360 N) and composite with 95 wt% LLM-105 and 5 wt% ternary (11–12 J). This improvement enables the composite explosives to be handled using standard procedures. Furthermore, the ability of the particles to accumulate electrostatic charge after cross-linking coating is significantly reduced, and PVC is more suitable as the contact material of CL-20 and composite particles than copper for use in the transportation and packaging. These findings can serve as a reference for wide application of CL-20.

Programming molecular switches in water and ethanol via thermo-sensitive polymers for phase control in energetic crystals

The practical application of energetic materials, particularly 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20), is frequently impeded by phase transition challenges. In this study, we propose a novel strategy to enhance the stability of CL-20 by employing a thermo-sensitive polymer, poly(N-isopropylacrylamide) (PNIPAM), to modulate its phase transitions. Our approach involves the use of an in-situ polymerized polydopamine (PDA) shell as a platform for surface grafting through atom transfer radical polymerization, yielding a core-shell structured CL-20@PDA-PNIPAM. Through comprehensive characterization, the successful grafting of PNIPAM is confirmed, significantly enhanced the phase stability of CL-20. Notably, our core-shell structure exhibits a 13 °C increase in phase transition temperature compared to raw CL-20, thereby delaying the ε→α phase transition by over 80 min under combined thermal and solvent conditions. The enhanced stability is attributed to the hydrophobic nature of PNIPAM above its low critical solution temperature in water, which effectively shields the CL-20 crystal. These findings provide new insights into enhancing the stability and safety of energetic materials in complex environments, highlighting the potential of our molecular switch mechanism.

The GO composite coatings for enhancing interfacial interaction performance and desensitization of CL-20

Although CL-20 is one of the most widely used high-explosives, the issue of its high sensibility and interfacial interaction with coating material in composite explosives have not yet been well understood. Herein, the electrostatic self-assembly capability of a graphene oxide (GO) aqueous solution was utilized to desensitize CL-20 and enhance its interfacial interaction by preparing a CL-20@GO@desensitizer composite, which was prepared by the “one-pot” water suspension method. It was found that the CL-20@GO composite exhibited a compact GO cladding layer and demonstrated exceptional safety characteristics. On this basis, the structure and performance of three CL-20@GO@densitizer composites were characterized by SEM, XPS, ZETA, DSC, XRD, and mechanical sensitivity. The morphology of composites showed that GO@microcrystalline wax (MW) was evenly coated on the surface of CL-20 under the influence of ionic charge and -OH bonding. The surface analysis results indicated that three types of GO@desensitizer films possessed exceptional coating effectiveness. The thermal analyses results suggested that the CL-20@GO@ethylene propylene diene monomer (EPDM) endowed Ea of composite up to 351.43 kJ/mol, while, the Ea of CL-20@GO, CL-20@GO@MW and CL-20@GO@MW + EPDM were only 184.36 kJ/mol, 186.21 kJ/mol and 258.79 kJ/mol, respectively. Besides, the XRD results confirmed that the three films had not caused a transformation of the CL-20 crystal phase, which afforded process safety support for the further application of this composite particle. Due to the high thermal conductivity of desensitizer-film, the composite showed a advantage in mechanical sensitivity, which can reach to a level of 252 N and 10 J. These findings can provide a reference for enhancing surface performance and desensitization of CL-20.

Micromodulation of dual-shell CL-20/desensitizer interface based on in-situ assembly of tea polyphenols

Although the research on CL-20 crystals has reached a high level, the property of the explosive-desensitizer interface is a key concern for composite explosive applications. Herein, inspired by super adhesion performance on cup, the in-situ assembly ability of tea polyphenol (TP) was utilized to enhance the surface performance and desensitize CL-20. The five kinds of core-dual-shell composites were fabricated by the “one-pot” water suspension method under the influence of ionic charge, -OH bonding, and the structure like suction cup of ivy. They were characterized by SEM, XPS, TG-DSC, XRD, and mechanical sensitivity device. The morphology and surface analysis results indicated that TP and desensitizer were evenly coated on the surface of CL-20, forming a core-dual-shell structure. This provided a great structural contribution to its security. The thermal analysis results suggested that TP/microcrystalline wax (MW) was endowed with thermal decomposition activation energy (Ea) of CL-20 from 190.92 kJ/mol up to 200.99 kJ/mol. While, the Ea of CL-20/TP, CL-20/TP/GO, CL-20/TP/TPU, and CL-20/TP/TPU-PDA were only 189.33 kJ/mol, 190.61 kJ/mol, 199.77 kJ/mol, and 184.75 kJ/mol, respectively. Meanwhile, the TP/GO film reduced Tp0 of CL-20 from 218.15 ℃ to 208.21 ℃ and Tb from 220.27 ℃ to 210.14 ℃, respectively. Besides, the XRD results confirmed that the five films had not caused a transformation of the ε-CL-20 crystal phase, which afforded process safety support for the further application of these composite particles. Due to the properties of MW and the advantages of dual-shell composite structural, the TP/MW film brought mechanical sensitivity of CL-20 from 60 N and 3.5 J to 336 N and 8.97 J, closing to the level of PBXs with 95% LLM-105% and 5% ternary composite (11 J). These safety parameters indicate materiel of moderate sensitivity that possibly can be handled in accordance with standard procedures. Moreover, the particle coated with TP/TPU-PDA possessed better free-running property. These findings can provide reference for the large-scale application of CL-20.

Effect of microstructure on functional force and air explosion performance of CL-20-based aluminum-containing explosive

A solvent–non-solvent approach was used to create a CL-20-based aluminum-containing explosive with a composite structure. The SEM results demonstrate that the aluminum powder is equally embedded on the surface of the CL-20 crystal in the CL-20/Al explosive with a composite structure but the aluminum powder in the mechanically mixed CL-20/Al explosive is agglomerated and spread unevenly. The maximum expansion velocity of the composite structure CL-20/Al explosive was 17.74% higher than that of the mechanically mixed explosive in the cylinder test, and the acceleration ability of the CL-20/Al explosive with a composite structure to the cylinder wall is superior to that of the mechanically mixed explosive. In the air explosion test, the shock wave overpressure and impulse of the CL-20/Al explosive with a composite structure are superior to those of the mechanically mixed explosive, but as the distance increases, the gap between the two explosives gradually narrows until it is flat. The results of interfacial particle velocity show that the length of the reaction zone and duration of CL-20/Al explosives with composite structures are longer than those of mechanically mixed structures, and the interfacial particle velocity of CL-20/Al explosives with composite structures is higher than that of mechanically mixed structures.

Design and preparation of a novel nano-composite coating for desensitization of CL-20

Although 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) is one of the best high-energy explosives, its application is severely limited by its high sensitivity. Herein, a composite wax-film with interfacial crosslinking anti-falling was designed and fabricated to desensitize CL-20. It was filled with nano-silica powder (n-Si), nano-graphenes (n-GPNs) and multi-walled carbon nanotubes (MWCNTs) as insensitive enhancers. A unique and stable core-shell composite explosive was prepared, and characterized by DSC, SEM, TEM, XRD, XPS as well as mechanical sensitivity tests. The results suggested that the functional group interaction and structural strengthening between enhancers and microcrystalline wax (MW) further enhanced the desensitization ability of the composite film for CL-20. Because of the hydrogen bonding and thickening enhancement, the CL-20 crystal was uniformly coated with a nano-composite film. Three enhancers were demonstrated to be highly compatible with CL-20. In comparison with MW@CL-20, The Ea, Tp0 and Tb of the composites containing n-GPNs increased by >375.27 kJ·mol−1, 21.04 °C and 18.27 °C, respectively. The SEM and XPS results showed that the composite performed a complete core-shell structure with thermal softening resistance and superior coverage (98.20 %). The insensitive enhancer was also distributed and embedded in the MW-film matrix. Besides, the anti-fall and cross-linking properties of the film enable the mechanical sensitivity of the composite explosive to reach to a level better than that of WO3/Al nanothermite with 5 wt% polyaniline and polymer-bonded explosive (PBX) with 95 wt% LLM-105 and 5 wt% ternary composite. The heterogeneous composites demonstrated excellent mechanical safety and high energy performance. These findings can provide a reference for the efficient desensitization of CL-20.

Precise Regulation of Combustion Characteristics of High-Energy Composite Propellants by Incorporation of CL-20 Crystals Intercalated with Energetic Burn Rate Modifiers.

In this study, a 2D structured triaminoguanidine-glyoxal polymer with a high nitrogen content has been coordinated with metal ions to produce energetic metal complexes (TAGP-Ms) employed as energetic burn rate inhibitors. The metal ions (Ba2+, K+, and Ca2+) are elaborately selected based on their ability of suppressing the burn rate of composite propellants. The CL-20 crystals were intercalated with prepared TAGP-Ms materials via a solvent-antisolvent method for realization of the precise control on burning behaviors of studied propellants. The influence of TAGP-Ms inhibitors on thermal decomposition and combustion characteristics of high-energy composite propellants was evaluated using thermal analysis and a combustion diagnostic method. Results of TGA/DSC-FTIR measurements suggest that the thermal decomposition of CL-20-containing composite propellants was found to be constrained by varied degrees as a result of TAGP-Ms additions, in which the TAGP-K displays a stronger effect on suppressing the thermal decomposition of CL-20 compared with that of other TAGP-Ms. The FTIR spectra indicate that the primary gaseous phase products are composed of N2O, H2O, and CO2 in CL-20 decomposition, as well as by HCl, H2O, NO2, and N2O in the decomposition of AP for all studied composite propellants. The combustion characterizations show that the TAGP-K-containing composite propellant exhibits a significantly reduced rate of heat release but is associated with a higher flame radiation intensity increased by 4.2% compared with that of the reference propellant, which clearly implies that the TAGP-K is capable of suppressing the energy release rate while ensuring the high energetic features of propellants to be well maintained. Moreover, the burn rate pressure exponents are considerably decreased by ∼10% for the TAGP-K-containing propellants in comparison with those of propellants with the typical formulation, which strongly suggests that TGAP-Ms are promising candidates for tuning the combustion behaviors of composite propellants by influencing the decomposition processes of CL-20 and AP collectively.

Crystal morphology prediction of CL-20 and 1,4-DNI co-crystal at different temperatures.

The morphologies of hexanitrohexaazaisowurtzitane (CL-20) and 1,4-dinitroimidazole (1,4-DNI) co-crystal under vacuum or solvent at different temperatures were predicted. The CL-20/1,4-DNI co-crystal has six important growth crystal planes: (002), (011), (101), (11‒1), (110), (111). The areas of (002), (101), and (011) planes account for a relatively large proportion, which are important crystal planes that affect the crystal morphology. The crystal habits at different temperatures were simulated. The simulation results showed that the crystal plane attachment energy of CL-20 and 1,4-DNI co-crystal increases with the increase of temperature, indicating that the increase of temperature is conducive to the growth of crystal planes. The aspect ratio decreases with the increase of temperature and the morphology of co-crystal becomes more spherical at a higher temperature. The theoretical predictions are in good agreement with the experiment. The simulation results can provide guidance for the crystallization of CL-20/1,4-DNI to obtain a nearly spherical crystal morphology. The CL-20/1,4-DNI unit cell structure was geometrically optimized by the COMPASS force field. The AE model was used to predict the morphology of CL-20/1,4-DNI under vacuum, resulting in the most morphologically important growth planes. Ethyl acetate was selected as the solvent. The interaction energy between the solvent and the crystal plane, and the attachment energies in solvent at 298 K, 320 K, 340 K, 360 K, and 380 K were predicted. The NVT ensemble is used in the molecular dynamics calculation process. The simulation step is 1 fs and the total simulation time is 500 ps. The Andersen thermostat is selected as the temperature control method. In the potential energy calculation, the atom-based and Ewald methods were selected to calculate the van der Waals force and the electrostatic interaction force, respectively.

Mechanism of the Impact-Sensitivity Reduction of Energetic CL-20/TNT Cocrystals: A Nonequilibrium Molecular Dynamics Study

High-energy low-sensitivity explosives are research objectives in the field of energetic materials, and the formation of cocrystals is an important method to improve the safety of explosives. However, the sensitivity reduction mechanism of cocrystal explosives is still unclear. In this study, CL-20/TNT, CL-20 and TNT crystals were taken as research objects. On the basis of the ReaxFF-lg reactive force field, the propagation process of the wave front in the crystals at different impact velocities was simulated. The molecular dynamics data were used to analyze the molecular structure changes and initial chemical reactions, and to explore the sensitivity reduction mechanism of the CL-20/TNT cocrystal. The results showed that the chemical reaction of the CL-20/TNT cocrystal, compared with the CL-20 single crystal, is different under different impact velocities. At an impact velocity of 2 km/s, polymerization and separation of the component molecules weakened the decomposition of CL-20. At an impact velocity of 3 km/s, the decay rates of CL-20 and TNT in the cocrystal decreased, and the intermediate products were enhanced, such as nitrogen oxides. At an impact velocity of 4 km/s, the cocrystal had little effect on the decay rates of the molecules and formation of CO2, but it enhanced formation of N2 and H2O. This may explain the reason for the impact-sensitivity reduction of the CL-20/TNT cocrystal.

Characterization and Analysis of Micromechanical Properties on DNTF and CL-20 Explosive Crystals

To study the crystal mechanical properties of 3,4-dinitrofurazanofuroxan (DNTF) and hexanitrohexaazaisowurtzitane (CL-20) deeply, the crystals of DNTF and CL-20 were prepared by the solvent evaporation method. The crystal micromechanical loading procedure was characterized by the nanoindentation method, and then obtained the mechanical parameters. In addition, the crystal fracture behaviors were investigated with scanning probe microscopy (SPM). The results show that the hardness for DNTF and CL-20 was 0.57 GPa and 0.84 GPa, and the elastic modulus was 10.34 GPa and 20.30 GPa, respectively. CL-20 obviously exhibits a higher hardness, elastic modulus and local energy-dissipation and a smaller elastic recovery ability of crystals than those of DNTF. CL-20 crystals are more prone to cracking and have a lower fracture toughness value than DNTF. Compared to DNTF crystals, CL-20 is a kind of brittle material with higher modulus, hardness and sensitivity than that of DNTF, making the ignition response more likely to happen.

Mussel-inspired interfacial reinforcement of thermoplastic polyurethane based energetic composites

The interfacial interaction and the microstructure evolution play a vital role in the mechanical properties of thermoplastic polyurethane (TPU) based energetic composites. In this work, inspired by the strong adhesion of mussels, 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) energetic crystals were coated with polydopamine (PDA) via in-situ polymerization of dopamine and then dispersed in TPU matrix. The core-shell structure of CL-20@PDA was confirmed by in-depth structural characterizations. The uniform and compact PDA shell gave rise to a high thermal stability with phase transition temperature of CL-20 crystals increased by 11.5 °C. Moreover, the PDA modification endowed the TPU based composites with excellent mechanical properties. A striking increase in mechanical properties and creep resistance was achieved with 6 h polymerization time of PDA. Compared with the PBX-Raw with untreated CL-20 crystals, the compressive and tensile strength after PDA coating increased by 115% and 57%, and the compressive and tensile fracture energy increased by 148% and 68%. The storage modulus at 25 °C was 40% higher than PBX-Raw. The enhancement effectivity could be ascribed to both interfacial interaction and the microstructure evolution of TPU binder. The theoretical simulations by molecular dynamics demonstrated the strong interfacial interaction mechanism between CL-20 and PDA. Moreover, the abundant hydrogen bonds between the hard segments of TPU and functional groups of PDA facilitated the formation of more hard microdomains which acted as physical crosslinking points to promote the phase separation. This work provides a potential method for the mechanical and thermal enhancement for TPU based energetic materials based on dopamine chemistry.

Investigation on the Evolution of Nano-Scale Defects of CL-20 Crystals under Thermal Treatment by Wide/Small-Angle X-ray Scattering.

Nano-scale crystal defects extremely affect the security and reliability of the explosive charges of weapons. In order to understand the evolution of nano-scale defects of 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaaza-isowurtzitane (CL-20) explosive crystals under thermal treatments, the specific surface, volume fraction and size distribution of the nano-scale defects were studied by using Wide Angle X-ray Scattering (WAXS) and Small Angle X-ray Scattering (SAXS) during the temperature range from 30 °C to 200 °C. The results showed that the number and size of the pores in CL-20 powder did not change significantly during the heating process before phase transformation (30–160 °C). At 170 °C, CL-20 began to convert from ε- to γ- phase, and the specific surface and volume fraction of the nano-scale defects increased significantly. Further investigation of the pore size distribution showed that the number of pores with a small size (radius 9–21 nm) changed particularly significantly, resulting from the cracking of the CL-20 crystal powder during phase transition. At 200 °C, the phase transition was completed and γ-CL-20 was created, and the small-sized pores gradually grew into medium-sized (radius 21–52 nm) pores over time when the temperature was fixed at 200 °C.

Tuning the Energetic Performance of CL-20 by Surface Modification Using Tannic Acid and Energetic Coordination Polymers

The energetic performance of hexanitrohexaazaisowurtzitane (CL-20) was modulated with two energetic coordination polymers (ECPs), [Cu(ANQ)2(NO3)2] and [Ni(CHZ)3](ClO4)2, in this study by a two-step method. First, tannic acid polymerized in situ on the surface of CL-20 crystals. Then, [Cu(ANQ)2(NO3)2] and [Ni(CHZ)3](ClO4)2 were hydrothermally formed on the surface of CL-20/TA, respectively. Explosion performance tests show that the impact sensitivity of the coated structure CL-20/TA/[Cu(ANQ)2(NO3)2] is 58% less than that of CL-20 with no energy decrease. On the other hand, CL-20/TA/[Ni(CHZ)3](ClO4)2 can be initiated by a low laser energy of 107.3 mJ (Nd:YAG, 1064 nm, 6.5 ns pulse width), whereas CL-20 cannot be initiated by even 4000 mJ laser energy. This study shows that it is feasible to modify the performance of CL-20 by introducing energetic CPs with certain properties, like high energy insensitive, laser-sensitive, etc., which could be a prospective method for designing high energy insensitive energetic materials in the future.

Largely desensitized and stabilized CL-20 crystals obtained through reinforcement with cross-linked graphene oxide

Preparation and structure of graphene intercalated CL-20 crystals.

Drop-weight impact ignition of CL-20 crystals caused by trapped gases: A high-speed photographic study

CL-20 explosive has a wide engineering application foresight due to its high energy while is limited by its mechanical sensitivity. In this regard, to study its ignition mechanisms under impact and to determine the main ignition sources, drop-weight experiments on CL-20 explosive crystals were carried out and recorded by a high-speed photography camera. Various configurations, e.g., film, ring, open ring and strips, were designed to explore primary ignition mechanisms and exclude secondary possible sources. The results show that the main ignition mechanism of CL-20 under drop-weight impact is the adiabatic compression of trapped gases. These trapped gases were mainly from the decomposition of CL-20 itself when melting. Our findings indicate that methods focusing on melting suppression should be considered to reduce the CL-20 sensitivity under impact.

Enhanced Crystal Stabilities of ε-CL-20 via Core-Shell Structured Energetic Composites

2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane (CL-20) is a widely used high-energy explosive for the application of energetic materials. However, the phase transformation from ε-CL-20 to γ-CL-20 restrains its further application in polymer bonded explosives (PBXs) and propellants. To inhibit the phase transition of CL-20, dopamine was first used in an efficient and facile method of in situ polymerization to passivate CL-20 crystals. The core-shell microcapsule particles were obtained, and the morphological characterization demonstrates the formation of a dense core-shell structure. The differential scanning calorimetry (DSC) and in situ X-ray diffraction (XRD) test results show that the compact and dense coating delays the ε-CL-20 crystal transformation temperature by about 30 °C, which enhances thermal stability. In addition, with the coating via polymers, the friction sensitivity of ε-CL-20 crystals decreases significantly. The findings indicate a successful application of dopamine chemistry in high-energy explosives, which provides an attractive method to modify the properties of CL-20 crystals.

Stabilization of ε-CL-20 crystals by a minor interfacial doping of polydopamine-coated graphene oxide

Hexanitrohexaazaisowurtzitane (CL-20) is a well-known high energy density nitramine, but it is of high sensitivity and has the problem of polymorphic transition. In order to reduce the sensitivity of ε-CL-20 and improve the stability of its crystal structure, the polydopamine (PDA)-coated graphene oxide (GO) was used to dope ε-CL-20 crystals by strategy of in-situ coating followed with a solvent-non-solvent crystallization process. It has been shown that modified CL-20 crystals with the best performances are of polygon shape with a smooth surface and with the average diameter of 16 μm, much smaller than that of raw ε-CL-20 (140 μm). In addition, the doping can either improve the polymorphic transition temperature up to 19.0 °C or exclude such a transition due to formation of completely new crystal phase with better stability, depending on the type and content of the dopants. The density of a certain GO@PDA modified CL-20 is even slightly higher than that of pristine ε-CL-20 due to better assembling of the molecules under the nucleation of the dopants. CL-20/PDAG-2 does not show any polymorphic transition peak. Moreover, the XRD spectrum of CL-20/PDAG-2 also demonstrates that it is a completely new crystal phase better than the other four reported ones in terms of thermal stability.

Multiscale design, interaction mechanism and performance of CL-20/Al energetic composites with embedded structure.

In order to design and prepare hexanitrohexaazaisowurtzitane/aluminum (CL-20/Al) composites, the contact state of CL-20 with aluminum particles under different mixed solvent contents were calculated with the method of dissipative particle dynamics (DPD). Then the modified attachment energy (AE) model was applied to predict the morphologies of CL-20 in ethyl acetate, hexane and ethyl acetate/hexane mixed solvents. Furthermore, the morphologies, the surface element distribution, the sensitivity and the energy performance of CL-20/Al composites prepared with the solvent/non-solvent method were characterized, and the interaction mechanism were also obtained. The results achieved show that phase separation phenomenon becomes obvious with the decrease of ethyl acetate/n-hexane mixed solvent content. CL-20/aluminum particles will form the composites of aluminum particles embedded in CL-20 crystal when the solvent content is zero. The order of modified attachment energies for ethyl acetate/hexane mixed solvents on CL-20 faces is (011) > (110) > (101) ≈ (11−1) ≈ (10−1) > (002). Besides that, the crystalline morphology of CL-20 in acetate/hexane mixed solvents is spindle-shaped. There are many Al particles embedded in CL-20 crystals of CL-20/Al composites prepared by using solvent/non-solvent method. The calculated results agree well with the experimental results. In CL-20/Al composites, aluminum particles interact with CL-20 mainly through hydrogen bond and strong van der Waals force. The sensitivity of CL-20/Al composites decreased obviously compared with pure CL-20 and mechanical mixing composites. Besides, the CL-20/Al composites with embedded structure can increase the explosion reaction temperature to 791.2 K, which has obvious energy advantage compared with CL-20/Al physical mixture.

Chemical reactions of a CL-20 crystal under heat and shock determined by ReaxFF reactive molecular dynamics simulations.

Studying the chemical reactions of hexanitrohexaazaisowurtzitane (CL-20) under heat and shock is helpful to understand its sensitivity and shock initiation mechanism. In this work, several molecular dynamics simulations were performed under three different conditions: high temperature, high temperature and pressure, and shock. The formation and breakage of chemical bonds, changes of bond lengths, and initial reactions were analysed. It was found that the main small-molecule product of CL-20 during initial decomposition under the three different conditions was always NO2, but the generation pathways were different. At high temperatures, NO2 was generated by the direct cleavage of N-NO2 bonds. In contrast, high pressure and shock promoted the transfer of O atoms to N atoms connected to NO2, leading to the breakage of N-NO2 bonds. Almost all NO2 originated from the transfer of O atoms under the shock conditions.