Abstract:

Abstract:

Abstract:The improvement of physicochemical properties of explosives by the way of cocrystallization has become a research hotspot in the field of energetic materials, the formation of cocrystal explosive is mostly driven by the intermolecular interactions, and their energy level transitions are located in the detection range of THz spectra. In this work, taking hexanitrohexaazaisowurtzitane(CL-20)/cyclotetramethylenete-tranitramine(HMX) cocrystal as the model system, the THz spectra of cocrystal components β-HMX, CL-20, and CL-20/HMX cocrystal were theoretically studied by combining the methods of molecular dynamics simulation and quantum mechanics. The assignment and analysis of vibration modes for characteristic peaks were carried out. The response of different intermolecular interactions in THz spectra was confirmed. Results show that compared with the cocrystal components CL-20 and HMX, the new characteristic absorption peaks of CL-20/HMX cocrystal located at 0.25, 0.49, 1.1, 1.47, 1.73, 2.27 THz and 3.7 THz respectively are found. Among them, the absorption peaks at 1.1, 1.47 THz and 1.73 THz are caused by intermolecular C—H…O hydrogen-bond, whereas the absorption peak at 1.73 THz is mainly assigned as the heterogeneous intermolecular hydrogen bonds.

Abstract:The thermodynamic parameters and the excited states of radiolysis products of 1, 3, 5-triamino-2, 4, 6-trinitrobenzene(TATB) were obtained by density functional theory calculation(DFT). The formation of benzoxadiazol-containing radiolysis products of TATB was found to be a thermodynamically spontaneous process, and the red shift of ultraviolet spectrum for benzoxadiazol-containing radiolysis products was confirmed through excited state calculation. The gamma-ray radiolysis products of TATB were studied by high-resolution electrospray ionization mass spectrometry(ESI-MS). Benzoxadiazol-containing radiolysis products of TATB were identified, which lead to the colour change of TATB. Calculated and experimental results revealed that benzoxadiazol-containing compounds were the main radiolysis products of TATB and a new endothermic peak in 600-700 nm, the reason of TATB colour change.

Abstract:To investigate the influence of meso-structure of polymer bonded explosive(PBX) on the effective elastic modulus of PBX, several meso-scale numerical models were analyzed and compared by finite element method, including hexagonal particle models, circular particle models in different particle distributions and irregular polygonal particle models established by Voronoi method. Results indicate that particle shape and distribution have remarkable influences on the effective modulus of PBX. Voronoi numerical model can not only achieve the high filling degree(>85%)of particle for PBX material, but also the meso-structure of PBX can be better resembled by irregular polygonal particle. Young′s modulus predicted by Voronoi model is 1.41 GPa, which is close to the experimental value. With increasing the particle content, Young′s modulus, bulk modulus and shear modulus increase in approximate exponent, while Poisson′s ratio decreases rapidly.

Abstract:To accurately predict the enthalpies of formation of all-nitrogen materials, nine density functionals including B3PW91, B3P86, B3LYP, X3LYP, O3LYP, M052X, M062X, M06HF, B2PLYP52 were employed to calculate the enthalpies of formation of nitrogen-rich compounds via atomization reaction. The calculation results show that double hybrid functional B2PLYP has the smallest mean absolute deviation of 30.1 kJ·mol^-1, which is more accurate than G4 method. Hence, the enthalpies of formation of five all-nitrogen molecules with cage structure, namely, N₄(T_d), N₆(D_3h), N₈(O_h), N₁₀(D_5h), and N₁₂(D_6h), were predicted by B2PLYP functional, and the corresponding results were 756.4, 1338.2, 1878.5, 2144.3, 2787.0 kJ·mol^-1, respectively.

Abstract:In order to understand the phenomenon and mechanism of thermal ignition and hot spots growth in energetic materials, spatiotemporal behaviors of thermal shock propagation in CL-20/TNT co-crystal and initial chemical reaction process were studied by first principles based ReaxFF reactive force field molecular dynamics simulations. Thermal shock mechanical wave induced by continuous fast heating of two ends in energetic materials and keeping it at high temperatures combining NVT ensemble and Berendsen temperature coupling method. In addition, two kinds of high temperature conditions (3000, 4000 K) were set up to study the influence of temperature difference on the initial thermal decomposition rate. When thermal loading is 4000 K, particle instantaneous translation rate can reach 0.5 km·s^-1 in early thermal shock propagation process, higher than the situation of 3000 K. At the same time, high temperature will lead co-crystal energetic materials decomposition. Here, molecule recognition algorithm is used to analyze the initial products and species. The decomposition rate of CL-20 is higher than that of TNT in the thermal shock propagation process under two kinds of thermal loading. The higher temperature of the thermal loading, the less time required to completely decompose. Product identification analysis shows that the main products of CL-20/TNT thermal decomposition are NO₂, NO, H₂O, N₂, CO, CO₂, HONO, H₂O₂, CHON, H₂N, CH₂O, where, NO₂ is the early initial thermal decomposition product, N₂, CO₂ and H₂O are the final products.

Abstract:Nanocomposite of Fe₂O₃ loaded on reduced graphene oxide (rGO) was prepared using hydrothermal (h-Fe₂O₃@rGO) and solvothermal (s-Fe₂O₃@rGO) method. Moreover, rGO and Fe₂O₃ nanoparticles (NPs) were prepared using solvothermal method. X-ray diffraction (XRD), Raman spectra and scanning electron microscope (SEM) was used to characterize the prepared Fe₂O₃ NPs, rGO, h-Fe₂O₃@rGO and s-Fe₂O₃@rGO. Differential scanning calorimeter (DSC) method was used to investigate the catalytic effects of h-Fe₂O₃@rGO, s-Fe₂O₃@rGO, rGO and Fe₂O₃ NPs on the thermal decomposition of TKX-50. As a result, s-Fe₂O₃@rGO prepared by solvothermal method avoids stack of rGO and has more uniform dispersion of loaded Fe₂O₃ NPs. h-Fe₂O₃@rGO, s-Fe₂O₃@rGO and Fe₂O₃ NPs can reduce the low decomposition peak temperature by 33.9, 10.9, 25.5 ℃ and 40.7 ℃, respectively. The apparent decomposition heat of TKX-50 increases to 1747, 1924, 2096 J·g^-1 and 2983 J·g^-1 due to the addition of h-Fe₂O₃@rGO and s-Fe₂O₃@rGO. s-Fe₂O₃@rGO has better catalytic effect on thermal decomposition of TKX-50 than h-Fe₂O₃@rGO and Fe₂O₃ NPs.

Abstract:Three kinds of energetic ionic salts, dimethylaminium salt (DMAB), 1, 3-propanediaminium salt (PDAB) and 1, 4-butanediaminium salt (BDAB) of 3, 6-bis(1 H-1, 2, 3, 4-tetrazol-5-yl-amino)-s-tetrazine(BTATz) were synthesized. The structures of DMAB, PDAB and BDAB were characterized by IR, ¹H NMR, ¹³C NMR and elemental analyses. The crystal structure of PDAB was determined by X-ray single crystal diffraction. The detonation velocity (D) and detonation pressure (p) of PDAB were calculated. The thermal decomposition behaviors of DMAB, PDAB and BDAB were studied by DSC and TG-DTG. The self-accelerating decomposition temperature (T_SADT), the critical temperature of thermal explosion (T_b), the thermal ignition temperature (T_TIT) and adiabatic time-to-explosion (t_TIAD) were calculated. Results show that the crystal of PDAB is monoclinic, space group C2/c with crystal parameters of a=2.2699(10) nm, b=0.5098(2) nm, c=1.6449(6) nm, β=93.045(15)°, V=1.9008(13) nm³, D_c=1.504 g·cm^-3, Z=4, F(000)=912, μ=0.127 mm^-1, R₁=0.0673 and wR₂=0.2002. The values of D and p of PDAB are 8862.09 m· s^-1 and 32.15 GPa, respectively. The values of T_SADT of DMAB、PDAB and BDAB are 576.87 K, 511.90 K and 521.55 K, respectively, revealing that DMAB has higher thermal stability than PDAB and BDAB. DMAB, PDAB and BDAB can be used as potential energetic materials and the property of DMAB is better than that of PDAB and BDAB.

Abstract:The single crystal of N, N′-bis(2-fluoro-2, 2′-dinitroethyl)-3, 4-diaminofurazan (LLM-208) was cultivated by solvent evaporation using anhydrous methanol as solvent at the temperature of 10-15 ℃. Its crystal structure was determined by a X-ray single-crystal diffractometer. Results show that the crystal density of LLM-208 is 1.895 g·cm^-3 at 130 K and 1.848 g·cm^-3 at 298 K, which belongs to monoclinic system, space group C2, a=19.225(5) Å, b=5.5779(15) Å, c=6.4176(17) Å, β=108.551(5)°, V=909.4(6)ų, Z=2, μ=0.192 mm^-1, F(000)=376. Hirshfeld-surface analysis suggests that the dominant contacts and distributions of LLM-208 crystal are shown as follows (R represents ratio): R_O…H/H…O=35.0%, R_O…O=22.3%, R_{F…O/C…F/ F…F}=12.5%. The activation energies calculated by using Kissinger, Flynn-Wall-Ozawa and Starink methods are 112.28, 114.49, 112.49 kJ·mol^-1, respectively. The pre-exponential factor by Kissinger method is 10^21.30 s^-1.

Abstract:4, 4′-Bis(chlorodinitromethyl)-3, 3′-azofurazan(BCNAF) was synthesized by using 4, 4′-dicyano-3, 3′-azofurazan as the starting material. The single crystal of target compound was cultivated by slow evaporation from methanol and its crystal structure was determined by X-ray single-crystal diffraction. Results show that it belongs to monoclinic system, space group P2₁/n, with cell parameters of a=7.5846(14) Å, b=8.4227(15) Å, c=12.324(2) Å, β=90.880(4)°, V=787.2(2) ų, Z=2, μ=0.494 mm^-1, F(000)=440. Crystal packing suggests that BCNAF is stabilized by highly symmetric structure, intermolecular π-π interaction as well as intramolecular halogen bonds. The thermal behavior of 4, 4′-bis(chlorodinitromethyl)-3, 3′-azofurazan was studied by using DSC-TG instrument, which showed that its decomposition peak was 142 ℃. Its calculated heats of formation is 816.5 kJ·mol^-1 by using Guassian09 and isodesmic reactions, which is higher than that of RDX. Its calculated detonation velocity (D) and detonation pressure (p) by EXPLO5 code are 8400 m·s^-1 and 30.8 GPa, respectively, which are close to those of RDX.

Abstract:To explore the best solvent of swelling the nitrocellulose(NC)/nitroglycerin(NG) absorbent tablets and the influence of predrying treatment on the swelling behaviors of absorbent tablet, the free swelling process of absorbent tablet with or without predrying treatment in single solvent such as acetone and ethyl acetate and mixed solvents such as ether/ethanol, ethanol/acetone and ethanol/ethyl acetate et aletc., was studied using the weighting method. One dimension diffusion behaviors of solvents, acetone, ethyl acetate and ethanol/ether (V_ethanol:V_ether=1:2) in absorbent bar were studied by "line tracing method". The free swelling kinetic equations of the absorbent tablets in various solvents and one dimension diffusion equations of three solvents, acetone, ethyl acetate and ethanol/ether (V_ethanol:V_ether=1:2) in absorbent bar were obtained. Results show that from the comprehensive consideration of swelling rate and equilibrium swelling degree, the comprehensive swelling effect of ethyl acetate and ethanol/ethyl acetate are the best for absorbent tablets. The predrying treatment can improve the equilibrium swelling degree and initial swelling rate of absorbent tablets in the solvents. There is no direct correlation between the swelling rate of absorbent tablet in the solvents and "one dimension diffusion" rate of solvents in absorbent tablets.

Abstract:In order to improve the detection performance of the fluorescent probe to the peroxide explosives, hydrogen peroxide (H₂O₂) is typically taken as a signature compounds, and a new method for H₂O₂ will facilitate security monitoring of peroxide explosives. In this study, a novel fluorescent probe (4-(4-nitro-benzyl)-boron-dipyrromethene, BD-3) was firstly designed and synthesized by using benzyl as the recognition group and boron-dipyrromethene (BODIPY) as the fluorophore. Meanwhile, the chemical structure of BD-3 was characterized and its detection performance was investigated. The fluorescence of BD-3 itself was very weak with the maximum absorption/emission wavelength of 500/508 nm. When BD-3 was fully reacted with H₂O₂, the fluorescence intensity of BD-3 was increased by approximately 11-fold and observed by the naked eye. The Turn-on fluorescence of BD-3 with response to H₂O₂ was based on the mechanism of photo induced electron transfer (PET). The linear range of BD-3 responding to H₂O₂ was from 1×10^-6 to 1×10^-4 mol·L^-1 with the correlation coefficient of 0.9998, and the detection limit was 0.9 μmol·L^-1. In addition, BD-3 displayed good photo-stability and high selectivity when responded to H₂O₂. In conclusion, this new probe BD-3 had many advantages of good photo-stability, high selectivity and fluorescence enhancement to H₂O₂, and it could meet the requirement of on-site detection of peroxide explosives under complex environmental conditions.

Abstract:1, 2, 4-Oxadiazoles are a new class of energetic materials, which have the features of high density, high oxygen balance and insensitivity. In this paper, the latest organic synthesis achievements of more than 30 oxadiazole energetic compounds base on mono-1, 2, 4-oxadiazoles, azo-1, 2, 4-oxadiazoles and bis-1, 2, 4-oxadiazoles were reviewed, and their performances were also introduced in detail. 1, 2, 4-oxadiazoles would be new choice as chlorine-free oxidizers due to its advantages.

Abstract:3-Fluorodinitromethyl-1, 2, 4-triazole(FDNMT) was synthesized using 3-cyano-1, 2, 4-triazole as starting material by the reactions of oximation, diazotization-chlorination, nitration, reduction and fluorination. The structures of all compounds were confirmed by IR, ¹H NMR, ¹³C NMR, elemental analysis and MS. The synthetic conditions of oximation reaction were optimized, the suitable conditions were as follows: molar ratio of 3-cyano-1, 2, 4-triazole and hydroxylamine hydrochloride was 1:1.15, pH value was 8-9, reaction time was 2 h, reaction temperature was at 60 ℃ with a yield of 49.0%. The single crystal of FDNMT was obtained in the acetonitrile system, and the crystal of FDNMT belongs to orthorhombic system, space group Pbcn, cell parameters: a=7.4821(11) Å, b＝9.8106(15) Å, c=38.683(6) Å, V＝2839.5(7) ų, Z＝16, μ＝0.178 mm^-1, F(000)＝1536. Based on the calculated(CBS-4M) heat of formation(-8.7 kJ·mol^-1) and the density (1.81 g·cm^-3), impressive values for the detonation parameters such as detonation velocity(8365.0 m·s^-1), detonation pressure (31.1 GPa) and detonation energy(5614.4 kJ·kg^-1) were computed using Kamlet-Jacobs equations.

Abstract:

Abstract:

Abstract: