Abstract:Semiconductor laser ignition system has not only been widely applied in safe and reliable ignition but also possesses obvious advantaged for anti-jamming in complex electromagnetic environment ，due to its small size, light mass and energy transmission by optical fiber. To investigate the ignition characteristics of laser igniter, a new type of semiconductor laser system and laser igniter filled with micron-sized B/KNO₃/PF were designed and prepared. TG-DSC, SEM, TEM, EDS, laser reflectance and Laser induced breakdown spectroscopy were used to study the thermal behavior, morphology, distribution of element, laser absorption efficiency, and emission spectra of B/KNO₃/PF. Then the ignition characteristics of B/KNO₃/PF igniter were studied by the semiconductor laser ignition system. The results showed that the initial reaction temperature of B/KNO₃/PF decreased and the heat release increased with the higher PF mass ratio and the smaller particle size in the DSC curve. The ignition process of the laser igniter can be divided into two stages: first ignition and secondary ignition. The pulse laser had a significant effect on the ignition characteristics of the igniter. The igniter could normally ignite with the 50% ignition energy of 6.23 mJ and 12.54 mJ, respectively, when the laser pulse were 5 ms and 10 ms. The first ignition delay time of 3.50-4.69 ms, secondary ignition delay time of 7.23-8.08 ms, and flame duration of 58-83.5 ms were produced in the laser igniter by changing the laser pulse and energy. The laser ignition system cannot motivate the igniter to fire normally when the laser pulse was 2 ms. These characteristics were consistent with the energy output law of semiconductor laser.

Abstract:In order to obtain the influence of barrel parameters on the laser-driven flyer velocity and morphology, the velocities and evolution process of laser-driven Al flyers confined by steel barrels with various diameters and lengths were investigated using Photonic Doppler Velocimetry (PDV) and Shadowgraph technique. The maximum velocity of 3100 m·s^-1 can be obtained when the diameter of the barrel was 800 μm, which is equal to the size of the Al flyer ablated by laser. When the diameter of the barrel was larger than 800 μm, it can not restrain the flyer effectively, and the velocity of the flyer decreased, which led to the lowest velocity of 2700 m·s^-1 with the barrel’s diameter of 1500 μm. When the diameter of the barrel was 600 μm, the energy around the flyer was wasted and the velocity of the flyer decreased to 2900 m·s^-1. The results also showed that flyer velocity decreased with the increase of the barrel length. Shadowgraph results showed that the Al flyer was fragmented and splashed around after it got away from the barrel exit, indicating that it was difficult for a 20 μm Al foil to maintain integral and planar when ablated by a pulsed laser.

Abstract:In order to investigate the effects of modulation period on the thermal properties and firing properties of Al/MoO₃ reactive films, Al/MoO₃ reactive film with 3 μm thickness was deposited by magnetron sputtering. The modulation period of Al/MoO₃ reactive film was 50 nm, 150 nm and 300 nm, respectively. The reaction process and energy of Al/MoO₃ reactive films were measured by DSC. The combustion speed of Al/MoO₃ reactive films were detected by high-speed camera. The initiators were integrated Al/MoO₃ reactive film with semiconductor bridge and bridge wire, and the current-firing sensitivities and voltage-firing sensitivities were also explored by Langlie method. The combustion speed was decreased from 5.35 m·s^-1 to 1.75 m·s^-1 as the modulation period increased from 50 nm to 300 nm. The 50% firing current of semiconductor bridge initiators was 1.44 A, 1.74 A and 1.87 A, and the 50% firing current of bridge wire initiators was 0.08 A, 0.65 A and 1.02 A when the modulation period of Al/MoO₃ reactive films was 50 nm, 150 nm and 300 nm, respectively. The bridge wire initiator can ignite the insensitive ignition composition of B-KNO₃ tablet with 1 mm ignition gap. The excellent firing parameters and outstanding ignition ability can lead to a remarkable optimization for the traditional electronic initiators.

Abstract:Three new nitrogen-rich energetic complexes Cu(DNABT)(NH₃)_2-x(NH₂NO₂)_x(x=0,1,2) were designed by incorporating N,N′-dinitroamino-bi(1,2,4-triazole) (DNABT) with copper, ammonia and nitramine. Their molecular, electronic and crystal structures, heat of formation, density, detonation performance and sensitivity were studied theoretically. The results show that the Cu and DNABT linked coordination bond is weaker than other bonds which possibly trigger the decomposition. The number of ammonia and nitramine ligands have a significant different effect on the structure and properties of the designed complex. All designed complexes possess high density (2.07-2.13 g·cm^-3), good energetic performance (detonation velocity: 8.44-9.12 km·s^-1, detonation pressure: 34.2-40.0 GPa) and acceptable sensitivity (7-22 cm), especially for the complex with x=1, whose energy is higher than RDXand similar sensitivity to RDX, being a potential high energy density compound.

Abstract:In order to explore the variation rule of explosives′ sensitivity in the external electric field, the bond lengths, nitro charges, bond dissociation energies of the potential trigger linkages and the impact sensitivities, electrostatic spark sensitivities as well as shock initiation pressures of the 1,4-dinitroimidazole-N-oxide (1,4-DNIO) explosive were investigated by the B3LYP/6-311++G(2d,p) and M06-2X/6-311++G(2d,p) levels of theory. Results show that the N─NO₂ bond is the most likely trigger linkage in the initiation reaction of explosive, followed by N→O, and finally the C─NO₂ bond in the external electric fields and the absence of the electric fields. Under the external electric fields along the positive directions of the N→O and C─NO₂ bond axes as well as the negative direction of the N─NO₂ bond axis, the dissociation energies of the N→O and C─NO₂ bonds are decreased, while those of N─NO₂ bond are increased, leading to the increases of the H₅₀ values and thus the decreases of the impact sensitivities. The opposite conclusion is drawn when the explosives are in the external electric fields with the reverse directions against the above cases. The changes in the bond lengths (ΔR), electron density values (Δρ), nitro charges (ΔQ), bond dissociation energy (ΔBDEs) of the trigger linkages and thoes in the impact sensitivities (ΔH₅₀) show good linear relationships withthe external electric field strengths, respectively. In most cases, the values of correlation coefficient R² are larger than 0.9500. The external electric fields have little effect on the electrostatic spark sensitivities or shock initiation pressures, accompanied by the variations lower than 0.5 J and 0.15MPa with the field strengths from –0.0010 a.u. to 0.0010 a.u., respectively.

Abstract:Hexanitrohexaazaisowurtzitane (CL-20) with a negative oxygen balance, is currently the most powerful commercially available explosive. In this work, the CL-20/H₂O₂ host-guest energetic material (CL-20/H₂O₂) was constructed by using urea hydrogen peroxide (UHP) as raw material through the solvent volatilization at low temperature and negative pressure. The structure of the complex was confirmed through X-ray diffraction (XRD) and Raman spectra. Results indicates that CL-20/H₂O₂ crystallizes in orthorhombic system space group Pbca with a long-range ordered stacked structure. The ratio of CL-20 molecule and H₂O₂ molecule is 2∶1 stoichiometry according to the thermogravimetry and simultaneous differential scanning calorimetry (TG-DSC) analyses. Furthermore, the polymorph transitions of CL-20/H₂O₂ with increasing temperature were investigated by in situ high temperature XRD. Results show that CL-20/H₂O₂ gradually converts to γ-CL-20 with elevated temperature and the rate of transition is faster than that of ε-CL-20. The CL-20 acetonitrile solvate (CL-20/CH₃CN) is a key intermediate via a solid state phase transition to form the CL-20/H₂O₂ host-guest energetic material by tracing the growing process of CL-20/H₂O₂.

Abstract:Ultrafine hexanitrohexaazaisowurtzitane/cyclotetramethylene tetranitramine(CL-20/HMX)cocrystal explosive was prepared by ultra-highly efficient mixing method. X-ray diffraction and differential scanning calorimetry were utilized to determine whether the cocrystal explosive was prepared. The crystal morphology, particle size, sensitivity of cocrystal explosive were characterized. The prepared samples were regular block-like ultrafine CL-20/HMX cocrystal explosives with uniform particle size of less than 1 μm, which appeared new stronger diffraction peaks at 11.558°, 13.264°, 18.601°, 24.474°, 33.785°, 36.269°. The purity of the CL-20/HMX cocrystal explosive was 92.6%. The thermal decomposition process of cocrystal explosives had only one exothermic decomposition stage with peak temperatures of 248.3 ℃. The enthalpy for the exothermic decomposition of the cocrystal (2912.1 J·g^-1) was remarkable higher than that of the physical mixture of CL-20 and HMX (1327.3 J·g^-1). According to GJB772A-1997《The explosive test method》, the friction sensitivity of CL-20/HMX cocrystal explosive was 84%, which was decreased by 16% compared with original CL-20, the characteristic height of the cocrystal was increased by 28.6 cm and 11.5 cm compared with original CL-20 and HMX, respectively. The compatibility of CL-20/HMX cocrystal with components of solid propellant, including hydroxyl-terminated glycidylazide polymer(HGAP), nitroglycerin/1,2,4-butanetriol trinitrate (NG/BTTN), triisocyanate(N-100), ammonium perchlorate(AP), aluminum powder(Al powder) were investigated by differential scanning calorimetry(DSC). The CL-20/HMX cocrystal was compatible with NG/BTTN, AP and Al powder, while incompatible with HGAP, N-100.

Abstract:In order to study the effect of iron tannate catalyst on thermal decomposition properties of common components in solid propellants, three submicron composite microspheres,tannic acid and iron (Ta-Fe)/ hexanitrohexaazaisowurtzitane (CL-20), Ta-Fe/ cyclotrimethylenetrinitramine (RDX) and Ta-Fe/ cyclotetramethylene tetranitramine (HMX), were prepared by ultrasonic spray drying. The morphology, particle size and composition of these composites were characterized by SEM and granulometer analyser. The effect of Ta-Fe on the thermal decomposition catalytic properties and kinetic parameters of CL-20, RDX and HMX were studied by differential scanning caloriometry (DSC). Results show that Ta-Fe distributes evenly with spherical particles and good dispersibility, and the particle size distribution range is 500-1000 nm. Ta-Fe effectively promotes the thermal decomposition of CL-20, RDX and HMX, whose peak thermal decomposition temperatures decrease by 17.2，8.2 ℃ and 11.5 ℃,respectively. Especially, Ta-Fe/CL-20 has the best catalytic effect, whose activation energy is 9.6 kJ·mol^-1 lower than raw CL-20.

Abstract:In order to analyze the cutting force response laws and cutting characteristics during PBX cutting process, the low-speed orthogonal cutting experiments, combined with the microphotography, 3D dynamometer and 3D surface profiler, were used to analyze the characteristics of instantaneous cutting force of PBX explosive simulants, and to study the cutting force response laws and key influencing factors in the cutting process of PBX explosive simulants. Results show that the dynamic cutting forces of PBX explosive simulants with different cutting depths are different. When cutting depth equals to 0.1 mm, the variation of peak cutting force is mainly caused by particles chip with curled up jet, and the cutting force curve exhibits subtle jagged variation. However, when the cutting depth equals to 0.3 mm or 0.5 mm, the peak cutting force mainly comes from the extension of material brittle fracture crack, the cutting force curve shows periodic large saw-tooth shape, and the zero point of f_z is at the over-cutting dent. The standard deviation of f_x shows significant variation at the cutting depth of 0.4 mm, which reflects the transition from continuous removal to brittle removal in the cutting state of explosive simulated materials. In low speed orthogonal cutting process, the influence of cutting width on cutting force is greater than that of cutting speed, and the cutting speed has little effect on cutting force.

Abstract:Thermo-decomposition performances of RDX and corresponding HMX-doping samples were studied comprehensively through microcalorimetric experiments. Thermo-decomposition curves and parameters without the influence of melting phase transition were simulated via decoupling peak separation method through AKTS software. The thermo-decomposition activation energies (E_a) of all the samples were calculated via Kissinger, Friedman and Ozawa methods, respectively. The results showed that RDX was belonging to melt decomposition materials. Its melting peak temperature was in the region of 201.07~208.05 ℃, while its decomposition peak temperature was in the range of 207.99~232.76 ℃. Its thermo-decomposition Ea value was 167.7 kJ·mol^-1 calculated via Kissinger method which was consistent well with the values which calculated via Friedman and Ozawa methods, respectively. The Ea values were further confirmed by AKTS simulated result. On the other hand, the melting and decomposition peak temperatures of HMX-doping samples were decreased with the doping of HMX. The precise decreased values were 8.63, 8.32, 9.70, 8.57 ℃ and 6.50 ℃ for melting peak temperatures and 1.14, 2.01, 2.58, 3.53 ℃ and 3.47 ℃ for decomposition peak temperatures with the RDX:HMX ratios of 9∶1, 8∶2, 7∶3, 6∶4, 5∶5, respectively. Notably, the thermo-decomposition E_a values of HMX-doping samples were also decreased with the increase content of HMX. The corresponding E_a values are 149.78, 151.40, 149.78, 132.93 kJ·mol^-1 and 132.93 kJ·mol^-1, respectively.

Abstract:The detection of trace trinitrotoluene (TNT) explosives by Surface Enhanced Raman Scattering (SERS) was studied. A novel organic metal framework ZIF-8@Ag composites material prepared by in situ growth was used as SERS substrates. Meanwhile, the structure and properties of the composites were characterized by field emission scanning electron microscopy (FE-SEM), transmission electron microscopy(TEM) and X-ray powder diffraction(XRD). Results show that the ZIF-8@Ag composites material has good SERS activity, and the enhancement factor is calculated as 8.84×10³. The probe 4-ATP is self-assembled on the surface of AgNPs. And it could selectively recognize TNT by the interaction of probe 4-ATP and TNT molecules. The detection limit is as low as 10^-9 mol·L^-1. In addition, the mechanism of the interaction between the probe 4-ATP and TNT was studied by ultraviolet spectroscopy, which found that TNT and 4-ATP formed Meisenheimer complex.

Abstract:Lead tannate (Ta-Pb) is usually used as a high-efficiency combustion catalyst for double-base propellants, but its catalytic efficiency is greatly affected by various factors such as chemical compositions and structure. Therefore, the catalytic performance of Ta-Pb is usually not predictable which limits its widely practical applications. In order to solve the above problems, the effects of Ta-Pb samples prepared by both lead oxide and lead acetate methods on the burning rate and pressure exponent of double-base propellants have been investigated. Furthermore, the catalytic combustion properties of Ta-Pb prepared under different conditions, such as different Pb²⁺ contents and pH values, were studied systematically. The results show that the catalytic performance of Ta-Pb prepared by using lead oxide as the starting material is better than the one prepared by using lead acetate. The burning rate of the double-base propellants increases first and then decreases with the increase of the Pb²⁺ content in Ta-Pb. When the molar ratio of tannic acid to lead oxide is 1∶5 (Pb²⁺ content is 31.95%), the as-prepared Ta-Pb has the best catalytic combustion performance, and the burning rate of propellants can reach 32.79 mm·s^-1 (at 16 MPa). The Ta-Pb sample obtained by adjusting the pH of the reaction system to neutrality has a significant effect on the combustion performance of the propellants. The optimumized conditions for the preparation of Ta-Pb is as follows: the preparation method is the lead oxide method, the molar ratio of tannic acid to lead oxide is 1∶5, and the pH is neutral. The Ta-Pb prepared under these conditions can increase the burning rate of the double-base propellants to 33.13 mm·s^-1 (16 MPa) and make the average pressure exponent less than 0.4 (12-16 MPa).

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