Hui Huang

Molecular dynamic simulations on the structures and properties of ɛ-CL-20(0 0 1)/F2314 PBX

Molecular dynamical (MD) simulations with the COMPASS force field were employed to investigate the influences of temperature (T), the concentration of F(2314) binder (W%), and crystal defects on the mechanical properties, binding energy (E(bind)), and detonation properties of epsilon-CL-20(001)/F(2314) PBX (polymer bonded explosives). T was found to have some influences on the mechanical properties, and the PBX at 298 K was considered with better mechanical properties. By radial distribution function g(r) analysis the three types of hydrogen bonds, H...O, H...F, and H...Cl were predicted as the main interaction formats between F(2314) and epsilon-CL-20, and the strength of these interactions changed with temperature changing. The isotropic properties of the PBX increased with W% increasing, but each modulus and E(bind) did not monotonously vary with W% increasing. The detonation properties of the PBX decreased with the increasing W%, and the PBX with 4.69% F(2314) was regarded with good detonation properties. The existence of crystal defects (vacancy or adulteration) might increase the elasticity but destabilize the system to some extent, and the mechanical properties of PBX were chiefly determined by the main body explosive. The above information was thought guidable for practical formulation design of PBX.

Initial chemical events in shocked octahydro-1,3,5,7-tetranitro-1,3,5,7- tetrazocine: A new initiation decomposition mechanism

We have performed ab initio molecular dynamics simulations in conjunction with the multiscale shock technique to study the initial chemical processes of octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX) under shock wave loading. The results show that the initial decomposition of shocked HMX is triggered by the N-O bond breaking and the ring opening. This will initiate many decomposition reactions and lead to the production of many small radicals at a moment. As the shock compression continues, these small radicals recombine to produce many large radicals and further form ring-shaped radicals. Then, these radicals begin to further decompose. It is also found that the system transiently produces a large number of metallic states under the shock compression. Our simulations thus suggest a new mechanism for the initial chemical processes of shocked HMX and provide fundamental insight into the initial mechanism at the atomistic level, which is of important implication for understanding and development of energetic materials.

Facile, continuous and large-scale synthesis of CL-20/HMX nano co-crystals with high-performance by ultrasonic spray-assisted electrostatic adsorption method

High-performance of CL-20/HMX nano co-crystals is readily synthesized by ultrasonic spray-assisted electrostatic adsorption method. This facile and continuous approach reduces handling time, minimizes the potential of aggregation via the electrostatic repulsive force among nano co-crystal particles and opens up new perspectives in fabricating various organic nano-sized co-crystals on a large-scale.

Ultrasonic approach to the synthesis of HMX@TATB core–shell microparticles with improved mechanical sensitivity

To improve the safety of sensitive explosive HMX while maintaining explosion performance, a moderately powerful but insensitive explosive TATB was used to coat HMX microparticles via a facile ultrasonic method. By using Estane as surface modifier and nano-sized TATB as the shell layer, the HMX@TATB core-shell microparticles with a monodisperse size and compact shell structure were successfully constructed. Both scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS) results confirmed the formation of perfect core-shell structured composites. Based on a systematic and comparative study of the effect of experimental conditions, a possible formation mechanism of core-shell structure was proposed in detail. Moreover, the perfect core-shell HMX@TATB microparticles exhibited a unique thermal behavior and significantly improved mechanical sensitivity compared with that of the physical mixture.

Cocrystal explosive hydrate of a powerful explosive, HNIW, with enhanced safety

A novel cocrystal explosive hydrate containing HNIW (hexanitrohexaazaisowurtzitane), NMP (N-methyl-2-pyrrolidone) and water was synthesized through cocrystallization. The crystal structure was characterized by power X-ray diffraction (PXRD) and single crystal X-ray diffraction (SXRD). This crystalline structure belongs to the monoclinic crystal system with space group P2(1)/c. The properties of the cocrystal hydrate including thermal behavior, impact sensitivity and detonation performance were also evaluated. The cocrystal hydrate shows a unique thermal behavior with an endothermic peak and a decomposition peak at 91 and 252 °C, respectively. Besides, the cocrystal hydrate displays an impact height with a 50% ignition probability of 112 cm, indicating a substantial reduction in impact sensitivity compared to pure α-HNIW and e-HNIW. Furthermore, although the power is diluted, the cocrystal hydrate is predicted to have better detonation performance than pure DNAN (2,4-dinitroanisole) and TNT (trinitrotoluene). Therefore, the cocrystal hydrate may be a promising low sensitivity explosive.

A novel model for the molecular dynamics simulation study on mechanical properties of HMX/F2311 polymer-bonded explosive

The ‘insert’ model for β-octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX)-based polymer-bonded explosive (PBX) was proposed for finding the relation of temperatures with mechanical properties. This model was simulated by using molecular dynamics models. The elastic constants and the effective moduli were calculated with static analysis method. Cauchy pressure was also calculated. It is found that the rigidity is weakened and the ductibility is improved by adding a small amount of F2311 in the crystalline HMX. The rigidity is also weakened with increasing temperature. However, the ductibility of HMX/F2311 PBX changes as a parabola with increasing temperature duo to the enhancement of F2311 molecular chain movement and simultaneously the increment of high energy conformation ratio in this molecular chain, i.e. the increment of the molecular chain rigidity.

Effect of microwave irradiation on TATB explosive (II): Temperature response and other risk

TATB (1,3,5-triamino-2,4,6-trinitrobenzene) explosives were safely irradiated with microwave and showed no visible change according to XPS and XRD spectra. Temperature of TATB sample increased quickly at the beginning and gently during sequent continuous irradiation with temperature less than 140 degrees C after 60 min, 480 W irradiation, and increased more quickly in 300 g at 480 W than in 150 g at 480 W, both implied that heat dissipation was in the majority of microwave energy. Two major risk factors in microwave irradiation were concerned including overheating which should be avoidable with temperature monitor and microwave discharge which should be controllable experimentally though dielectric breakdown mechanism was not elucidated theoretically yet.

A DFT study of five-membered nitrogen-containing fused heterocycles for insensitive highly energetic materials

A series of molecules with conjugated backbones combined with two five-membered nitrogen-containing rings is suggested for the design of new energetic compounds. With the participation of both –NH2 and –NO2, seven planar derivatives were characterized with aromaticity and intramolecular hydrogen bonds. The geometrical and electronic structures, gas and condensed-phase heats of formation (HOFs) and strengths of the hydrogen bonds were studied using density functional theory methods. The crystal structures of these compounds were predicted using molecular packing calculations. The bond dissociation energies (BDEs) were investigated to understand their stabilities. Our calculated results indicate that these compounds are promising candidates for energetic materials. Among them, two compounds with a B4 backbone, B4-1 and B4-2, possess high densities, great HOFs and detonation properties. B4-2 has not only a high density of 2.263 g cm−3, heat of formation of 106.91 kcal mol−1, detonation velocity of 9.74 km s−1 and pressure of 47.79 GPa, but also a high BDE of 62.72 kcal mol−1 and layered crystal packing, and can be considered as a potential candidate for high energetic materials with great insensitivity.

Theoretical studies on the derivatives of tris([1,2,4]triazolo)[4,3-a:4′,3′-c:4′′,3′′-e][1,3,5]triazine as high energetic compounds

A heterocyclic framework inherited from triazole and triazine was suggested for the design of new energetic compounds. The geometric and electronic structures, IR spectra, gas and condensed-phase heat of formation of tris([1,2,4]triazolo)[4,3-a:4′,3′-c:4′′,3′′-e][1,3,5]triazine (TTT) and its nitro, amino, nitramino, and azide functionalized derivatives have been studied with ab initio and density functional theory methods. The crystal structures of these compounds were predicted using the crystal packing model. The initial decomposition reactions in the gas phase were studied to examine their kinetic stability. Our calculated results indicate that these compounds are promising candidates for energetic materials. In particular, 3,7,11-trinitrotris([1,2,4]triazolo)[4,3-a:4′,3′-c:4′′,3′′-e][1,3,5]triazine (TNTTT) has a density of 2.031 g cm−3, heat of formation of 208.37 kcal mol−1, detonation velocity of 10.55 km s−1, pressure of 38.57 GPa, and high activation energy of 55.97 kcal mol−1, which are in general better than the commonly used energetic materials.

Polarization response of clathrate hydrates capsulated with guest molecules

Clathrate hydrates are characterized by their water cages encapsulating various guest atoms or molecules. The polarization effect of these guest-cage complexes was studied with combined density functional theory and finite-field calculations. An addition rule was noted for these systems whose total polarizability is approximately equal to the polarizability sum of the guest and the cage. However, their distributional polarizability computed with Hirshfeld partitioning scheme indicates that the guest-cage interaction has considerable influence on their polarization response. The polarization of encapsulated guest is reduced while the polarization of water cage is enhanced. The counteraction of these two opposite effects leads to the almost unchanged total polarizability. Further analysis reveals that the reduced polarizability of encapsulated guest results from the shielding effect of water cage against the external field and the enhanced polarizability of water cage from the enhanced bonding of hydrogen bonds among water molecules. Although the charge transfer through the hydrogen bonds is rather small in the water cage, the polarization response of clathrate hydrates is sensitive to the changes of hydrogen bonding strength. The guest encapsulation strengthens the hydrogen bonding network and leads to enhanced polarizability.