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Abstract:Based on the preparation technology of non-deuterated HMX using paraformaldehyde as raw material, deuterated octagon(β-HMX-d₈) was successfully synthesized with a total yield of 58.5% from deuterated paraformaldehyde. The β-HMX-d₈ was obtained via recrystallization method using acetone as the crystal transformation solvent. The intermediates and final products were characterized by ultraviolet-visible spectroscopy (UV-Vis), Fourier transform infrared(FT-IR) spectroscopy, ¹H-nuclear magnetic resonance(¹H NMR) spectroscopy, ¹³C-nuclear magnetic resonance(¹³C NMR) spectroscopy, thermogravimetry-derivative thermogravimetry (TG-DTG), differential scanning calorimetry(DSC), or x-ray powder diffraction(XRD). The deuterated ratio of systhesized β-HMX-d₈ is 99.75% measured by NMR method with maleic anhydride as an internal standard. The purity of HMX-d₈ is 99.27% determined by HPLC via area normalization method.

Abstract:The solubility of 1-methyl-3, 4, 5-trinitropyrazole (MTNP) in different solvents was determined by the gravimetric method. The Apelblat equation and vant′t Hoff equation were used to correlate the solubility data. The standard enthalpy of dissolution, standard entropy of dissolution, standard Gibbs free energy of dissolution, solid-liquid surface tension and surface entropy factor of MTNP were estimated by the experimental data. By comparing the solubility data of MTNP, benzene, methanol and ethanol absolute were used to crystallization as solvent and the product was characterized. Results show that the solubility of MTNP increases with increasing the temperature. The mean absolute percentage deviation between the fitted and experimental values of the Apelblat and vant′t Hoff equation is less than 5.18%, but the experimental data correlated by the Apelblat equation is superior. The morphology of the product crystallized using ethanol absolute observed by electron microscopy is regular and uniform. The impact sensitivity of product crystallized by ethanol absolute is 68%. The size uniformity of product measured by the BT-2002 laser particle size analyzer is better.

Abstract:To study the quasi-isentropic compression of solid explosive, a graded areal density flyer termed the 'bed of nails'(BON) was used. Through changing the flying spike height combined with gun loading technology and aluminum base multiple electromagnetic particle velocity gauge technique, when the buffer layer after the flyer spike hit the buffer layer then impacted the solid explosive, the quasi-isentropic compression process generated by the front surface and inside of the explosive were tested and captured. The particle velocity at front surface and different depths of explosive inside was measured by Al-based multiple electromagnetic particle velocity gauge. The shock wave tracer was used to capture the time of shock wave reaching each depth of the explosive. The comparative experiments with different peak heights were performed. Results show that the quasi-isentropic compression duration of front surface of target are 0.37 μs for JB-9014 target and 0.22 μs for PTEF target when the flyer spike height is 2.5 mm. The front surface of the target has complete quasi-isentropic compression process and inside the target has completed the process of quasi-isentropic compression to impact. The x-t diagram of shock wave shows that the velocity of shock wave in the target is stable at the early stage, and it attenuates at later stage. When the flyer spike height and the thickness of the buffer layer are properly allocated, the quasi isentropic compression process with a wider time will take place in the target sample.

Abstract:To investigate the effect of Al particle size on the quasi-static compression reaction and drop hammer impact sensitivity of aluminum-polytetrafluoroethylene (Al-PTFE), six types of Al-PTFE reactive material specimens with different Al particle size were prepared by molding sintering method and were comparatively tested by universal testing machine and drop hammer machine, and observed by high-speed photography instrument. The stress-strain curves and impact sensitivity data of different specimens were obtained, and the effect of Al particle size on the quasi-static compression mechanical properties and impact sensitivity of Al-PTFE was analyzed. Results show that in quasi-static compression test, the reaction of specimen with Al particle size less than 10 μm is occurred while the reaction of specimen with Al particle size larger than 10 μm does not occur. In drop hammer impact test, the reaction for six types of Al-PTFE specimens all is occurred. With the increase of Al particle size, the strength and sensitivity of specimens decrease, the toughness of specimens first increases and then decreases, reaching the maximum at 6-7 μm. The activation of Al-PTFE reactive material become more and more difficult to occur with the increase of Al particle size in lower strain rate range (10^-2-10² s^-1).

Abstract:To reduce the effect of formability, combustion duration, burning rate and other parameters of the chemical igniter on the dust combustion and explosion experiments and improve the accuracy and repeatability of experimental data, the chemical igniter coated with a polyvinyl acetate (PVAc) elastic microsphere was developed. Firstly, the ignition powders were desensitized by paraffin wax, then a few drops of petroleum ether was added to the ignition powder to form a spherical ignition powder, then the spherical ignition powder was coated by ethanol solution of PVAc and dried in vacuum. In the process of drying, the petroleum ether was volatilized to make the coated film expand and the ignition powder bulk. The PVAc elastic hollow microsphere prepared has the advantages of good formability, strong toughness, water proof and oxidation resistance, etc. The deflagration characteristics of the igniter were studied by a high-speed camera and compared with other three types of igniters. The experimental results show that the igniter coated by PVAc elastic microsphere has a spherical flame propagation, a moderate flame velocity, and a stable ignition reliability, which can reduce the experimental data error of the dust explosion because of the influences of the igniter.

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Abstract:Based on the first-principle software developed by ourselves, the thermodynamic stability, mechanical properties, and detonation performances of structure for hexanitrohexaazaisowurtzitane(CL-20) explosive with five crystallline phase, benzotrifuroxane(BTF) crystal explosive and CL-20/BTF cocrystal explosive were studied. Results show that the electrostatic attraction effect of weak hydrogen bonds makes the intermolecular binding energy of CL-20/BTF cocrystal increase by 39% compared with that of hydrogen-free BTF crystal, which improves thermodynamic stability of cocrystal structure and significantly changes its mechanical properties, such as bulk modulus and sound speed etc. Although the BTF/CL-20 cocrystal and pure BTF crystal have the similar density, but due to the oxygen balance coefficient of the cocrystal has been optimized, so its detonation velocity and detonation pressure are improved by about 11% and 5%, respectively. Compared with the β-CL-20 crystal, the density and oxygen balance of the cocrystal are decreased, the detonation pressure and detonation velocity relatively decrease by about 15% and 6%, respectively. Design of a new type of insensitive cocrystal explosive should avoid the molecule with extremely weak strength covalent bonds and structure with characteristic peaks of high density vibration spectrum, thermodynamic stability effect of hydrogen bond on the molecular space packing should be effectively used, and the hydrogen element content should be moderately controlled to protect the high energy density of explosives.

Abstract:To accurately understand the effect of solvent and temperature on crystal morphology of energetic materials, molecular dynamics simulations were employed to investigate the crystal morphologies of 1, 1-diamino-2, 2-dinitroethene (FOX-7) under H₂O/dimethylacetamide (DMF) condition. By calculating the interaction energies of solvent and crystal surfaces, the attachment energies in vacuum were modified and the crystal shapes in different ratio of solvents with different temperatures were obtained. The intermolecular interactions of solvent molecules and crystal surfaces were also discussed. Results show that the morphologically dominant faces of FOX-7 in vacuum are (0 1 1), (1 0 -1), (1 0 1), (1 1 -1), (0 0 2) and (1 1 0), the crystal morphologies of FOX-7 in H₂O/DMF solutions are variable in different temperatures, the crystal shape is similar to block in different ratio of solutions in 298 K, and the predicted crystal morphology was in agreement with the experimental result from the reference.

Abstract:The initiation and subsequent decomposition mechanisms of α-RDX crystal under high temperature (3000 K) coupled with detonation pressure (34.5 GPa) were studied by ab initio molecular dynamics simulations. The crystal structure of RDX was relaxed using two types of van der Waals corrections such as PBEG06 and PBETS functional at ambient conditions. The results indicate that the PBEG06 functional is much suitable for studying α-RDX. Results show that the decomposition of α-RDX is triggered by the homolysis of the C—H bond. The DOS clearly validates that the C—H bond is broken. The elimination reaction of HONO during the decomposition is observed. The primary reactions for producing NO₂, NO, N₂O, N₂, HONO, N₂O₄, H, O—H, H₂O, and CO₂ occur at very early stages. After the initiation of RDX, there are three different subsequent decomposition pathways. There are three main interesting subsequent decomposition paths include: (1) the C—N bond hemolysis triggers the other C—N bonds of this ring to break; (2) the dissociation of N—NO₂ bond releases NO₂ gas; (3) the H radical attacks the O atom to release O—H radical by forming O—H bond.

Abstract:To explore the effect of interactions between insensitive high energy mixed-plasticizers and energetic binders on the system, taking nitrocellulose(NC) as binder, five kinds of blending models which contain 2-methyl-2-propane-1, 3-diyl dinitrate(TMETN), nitroglycerin(NG), and three kinds of TMETN/NG mixed-plasticizers with different mass ratio were constructed. The interactions, mechanical properties, radial distribution functions, and maximum trigger bond(O—NO₂) length (L_max)etc. parameters for each blending system were simulated by molecular dynamics method using Materials studio software. Results show that the binding energy of blending system is decreased when the content of TMETN is increased in the blending models. The mechanical properties of blending model containing mixed-plasticizers are better than those of blending model of single component plasticizer. When the mass ratio of NG to TMETN is 3:1, two kinds of nitrate plasticizers can establish strong hydrogen bond interactions with NC at the same time, and provide higher modulus and lower maximum trigger bond length for blending system, revealing that adjusting the mass ratio of mixed-plasticizers can enhance the interactions between compositions of each system thus the mechanical properties and stability of trigging bond of the blending system are improved.

Abstract:To study the detailed aging mechanisms of polyethylene glycol (PEG) adhesive, based on the B3LYP method of density functional theory (DFT) and canonical variational transition state theory combined with a small-curvature tunneling correction (CVT/SCT), the molecular simulation and calculation for the aging reaction type of PEG molecule in the presencee of PEG unimolecule and NO₂ molecule were carried out. Results show that there are two kinds of degradation breaking of C—O bond breaking reaction and hydrogen atom transfer reaction under the PEG unimolecular reaction condition. The bond dissociation energy of C(2)—O(2) bond is smaller than those of the chemical bonds O(1)—C(1) and C(1)—C(2), the C(2)—O(2) breaking is the trigger point of the cleavage reaction of PEG unimolecular. The hydrogen atom transfer reaction is the process of gradual transfer of hydrogen atom connected to C(1) to O(2) atom and the amount of heat absorbed by the reaction is 29.19 kJ·mol^-1. Under the participation of NO₂ molecule, there are three kinds of aging reaction modes, namely the degradation breaking reactions of PEG molecule, nitration reaction and cyclization reaction, the activation energies required is less than that of the aging reactions of PEG unimolecular.The change range of bond dissociation energies and activation energies required by aging reactions of PEG molecule with the polymerization degree of 2, 4, 6, 8 and 10 are less than 3 kJ·mol^-1, indicating that the polymerization degree has little effect on the reaction. At the storage temperature of 20-60 ℃, the rate constants of degradation breaking reactions and cyclization reaction under the participation of NO₂ molecule are 10³-10²⁸ times as much as that of hydrogen atom transfer reaction. The basic aging rule of PEG molecule in the presence of NO₂ molecule is obtained, considering that the cleavage reaction, nitration reaction and cyclization reaction for PEG under the participation of NO₂ molecule are the main aging modes, the hydrogen transfer reaction of PEG unimolecular are the secondary aging mode, while the occurrence of the C—O bond breaking reaction is the most difficult.

Abstract:To explore the applicability of the p-τ criterion, James criterion and Π-τ criterion to the one-dimensional shock initiation criterion of 2, 2′, 4, 4′, 6, 6′-hexanitrostilbene(HNS-Ⅳ) explosive, and study the feasibility of one-dimensional shock initiation of HNS-Ⅳ by flyer shock initiation model. The three criteria were fitted combined with reported experimental data and the best criterion equation was obtained. The influence of polyimide flyer with different thickness on HNS-Ⅳ velocity threshold was simulated by AUTODYN software, and the fitting of criterion curves were carried out based on the simulation results. The feasibility of investigating the one-dimensional shock initiation of HNS-Ⅳ was explored by flyer shock initiation model. The simulation results show that there is a deviation between the simulation result of the velocity threshold and the experimental one, which is caused by the change of shape and thickness during the flyer driving. In the fitting results, The R² of p-τ criterion, James criterion and Π-τ criterion are 0.9813, 0.8715 and 0.9940, respectively. The fitting result of Π-τ criterion is the best, and the simulation result is consistent with the literature ones. According to Π-τ criterion, the best criterion equation obtained by literature data and simulation data is Π=0.156+0.013/τ and Π=0.175+0.012/τ, respectively, two curves basically coincide with each other, indicating that investigating the one-dimensional shock initiation of HNS-Ⅳ is feasible through numerical simulation.

Abstract:The development process of self-propagating high-temperature synthesis (SHS) at home and abroad was briefly summarized. The components of the element system of SHS precursor and the application direction of SHS products (powdered functional materials, ceramic materials, coating materials) were classified and expounded and the application of future energetic materials in SHS was emphatically analyzed. Secondly, the theoretical analysis of ignition mechanism, reaction mechanism, thermodynamics and kinetics of SHS materials suitable for different application directions was emphatically analyzed. On this basis, a new viewpoint that the adiabatic temperature was not the only criterion of SHS reaction was proposed. Finally, the combustion mechanism of SHS was introduced and the effects of experimental conditions such as particle sizes of reactants, milling parameters and pressed compact pressure of reactants on the SHS reactions were clarified. At the same time, the problems in the development of the SHS technology were analyzed.

Abstract:The cocrystal of ammonium dinitramide(ADN)/18-crown-6(18C6) was prepared by solvent evaporation method, and its crystal structure was determined by X-ray single crystal diffraction(SXRD). The hygroscopicity of cocrystal was measured by weight gain method. Results show that the cocrystal belongs to monoclinic system, the space group is C₂/c with the unit cell parameters of a=23.935 (3) Å, b=8.6327 (11) Å, c=20.324 (3) Å, β= 112.874 (3)°, Z=8. The formation of the cocrystal mainly depends on medium strong N—H…O hydrogen bonds action. The formation of ADN/18C6 cocrystal structure makes the moisture absorption rate of AND reduce from18% to 1.2%.

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