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Abstract:In order to reduce the erosion effect of propellant, porous urea-formaldehyde resin microspheres were synthesized by stepwise polymerization of urea and formaldehyde without introducing templates and structure-directing agents. Nano-sized TiO₂ particles were deposited on the pores by sol-reflux method, and composite microspheres were formed as erosion inhibitors. SEM and particle size analysis showed that there were obvious mottled nanopores on the surface of urea-formaldehyde microspheres. Combined with FT-IR and XPS analysis, it was determined that nanopores could be used to deposit high purity nano-TiO₂. The particle size distribution of urea-formaldehyde/TiO₂ composite microspheres was in the range of 7-30 μm. Thermal analysis results showed that the inorganic content of the composite microspheres was about 6%. The composite microspheres exhibited good compatibility with the propellant, which did not affect the thermal decomposition of the propellant and was beneficial to improving the thermal stability of the propellant. The erosion inhibition performance of the composite microspheres was verified by the semi-closed bomb test. When the composite microspheres had a mass ratio of 3.4% relative to the propellant, the effect was the best and the erosion-reducing efficiency was 20.5%. This composite material is expected to be applied to the modification of standard propellants and the design of new high-energy propellants.

Abstract:In order to investigate the combustion performance of four-hole cuboid gun propellants, a combustion physical model was established according to the structural characteristics of four-hole cuboid gun propellants. The Ψ-Ζ and Γ-Ψ curves were obtained through the Maple software. The theoretical combustion properties of four-hole cuboid gun propellants were compared with that of the cylindrical seven-hole and single-hole gun propellants under the same web size and length-to-diameter ratio. Meanwhile, the web size, length-to-diameter ratio and inner-hole diameter were researched as the main factors to the theoretical combustion properties. The results demonstrated that the four-hole cuboid gun propellant performed a good progressive combustion property when the length-to-diameter ratio was higher than 1.5, which was better than the cylindrical single-hole gun propellants. Although the four-hole cuboid gun propellant performed a worse combustion property than the cylindrical seven-hole gun propellant, it displayed the combustion split points in the latter point. Meanwhile, the four-hole cuboid gun propellant had a better progressive combustion property when the inner web size was the same as the outer, the length-to-diameter ratio was in the range from 1.5 to 3, and the inner-hole diameter was in the range from 0.10 mm to 0.20 mm. The experimental results agreed well with the theoretical analysis results, but the moulding process leaded to the certain deviation of inner hole, resulting in the splitting point reached in advance.

Abstract:In order to further improve the progressive combustion of 37-well propellant, a 37-well nitroguanidine propellant was coated by two-layer coating process. The effects of coating, compatibility of the coating layer and the base propellant, the content and layers of the coating on the combustion performance were investigated by Three-dimensional video microscopy, Scanning electron microscope, DSC and constant volume combustion test. The thickness of the double coated propellant was relatively uniform. The compatibility between coating layer and the propellant was good. When the coating content was 8%, the combustion enhancement value of the double-layer coated propellant was significantly higher than that of the single-layer coated propellant. The combustion enhancement value ΔL of the double-coated propellant increased at first and then decreased with the increasing of the outer coating layer. When the content of inner and outer coating layer was 5%, the progressive combustion was the largest, with ΔL of 0.1431 MPa^-1·s^-1, which increased by 43.53%, compared with the 37-well propellant.

Abstract:In order to solve the problem of high viscosity of high solid content propellants, supercritical carbon dioxide (SC-CO₂) has been used as a plasticizer to improve its rheological behavior. The in-line viscosity of the CA/CaCO₃ solution was measured by a slit die rheometer during the extrusion process assisted with SC-CO₂, and the Power law was used to describe the rheological behavior of CA/CaCO₃ and CA/CaCO₃/SC-CO₂ solutions. Polyflow was utilized to model the dispersive mixing properties of the CA/CaCO₃/SC-CO₂ solutions. Results show that with the presence of SC-CO₂, the viscosity and pressure of the CA/CaCO₃ solution decreases significantly.And the viscosity coefficient of the CA/CaCO₃ solution at 50℃ decreases by 26.00%, while its non-Newtonian index increases by approximately 16.67%. As the extrusion temperature increases, the viscosity of the CA/CaCO₃/SC-CO₂ solution decreases, and its shear viscosity is less sensitive to temperature at higher shear rate. According to this simulation results, when the CA/CaCO₃/SC-CO₂ solution is subjected to the maximum shear stress, the maximum probability density increases by 20.63% at 50 ℃, which confirms that SC-CO₂ improves the dispersion mixing properties of the CA/CaCO₃ solution.

Abstract:To study the microscopic damage characteristics of crack tip in the three-point bending process of hydroxyl-terminated polybutadiene(HTPB) propellant, the dynamic damage process of crack tip was observed by scanning electron microscopy. Based on submodel of propellant, a multi-scale model of three-point bending process was established. The macroscopic deformation and meso-damage of crack tip during three-point bending process were calculated. The damage process of crack tip was analyzed by experiment and numerical simulation, respectively. The results show that the damage process of the three-point bending test is firstly the dewetting of the particles at crack tip, and then from the damage zone. With the increase of the compression displacement, the microcrack caused by the dewetting of different particles converges with crack tip to make the crack develop. Due to the tensile action at both sides of the crack, the crack tip becomes blunt. As the compression displacement increases from 0 to 1.2 mm, the crack opening displacement increases from 0 to 84.1 μm, and the increase rate is also increased. The numerical simulation results agree well with the experimental results. The multi-scale numerical model based on submodel can effectively simulate the macroscopic deformation of propellant on three-point bending process and the microscopic damage process of crack tip, which provides a new method for the analysis of macroscopic and microscopic damage process of propellant.

Abstract:The mechanical properties, sensitivity and compatibility of polyethylene glycol (PEG)/nitroglycerin (NG)/trimethylolethane trinitrate (TMETN) blends were studied by molecular dynamics and mesoscopic dynamics simulations. The designed systems included PEG/NG、PEG/TMETN and PEG/NG/TMETN, in which the mass ratios of NG to TMETN were set to be 3∶1, 1∶1 and 1∶3, respectively. The PEG/TMETN blends have the best mechanical properties, lowest sensitivity and best compatibility. Considering the energy of TMETN was lower than NG, the mixed plasticizer " NG/TMETN" was a nice choice which combined "the high energy of NG" and " the excellent performance of TMETN". Specifically, the addition of TMETN into the PEG/NG blends resulted in the reduced sensitivity of the blends, the crystallinity of PEG and the self-aggregation of NG will be suppressed, together with improved compatibility. Although the mechanical properties of the PEG/NG/TMETN blends were slightly worse than these of the systems with single plasticizer, the properties can be improved by increasing the content of TMETN (NG∶TMETN=1∶3). The processability of PEG/NG/TMETN was good. The mechanical properties of the mixed plasticizer system were related with hydrogen bond, while the properties of single plasticizer systems were more affected by the nature and structure of the substance. The thermal sensitivity of the mixed plasticizer systems can be characterized by maximum length of trigger bond or cohesive energy density.

Abstract:Since the general nonlinear explicit dynamics software does not have a mathematical model suitable for simulating the action process of pyrotechnic actuated devices, the dynamics simulation can only be performed by multi-software co-simulation. In order to simplify the simulation process, the pressure-time history (p-t curves) of the pyrotechnic composition under constant volume conditions was simulated using the newly embedded deflagration equation of state of MSC.Dytran software. Simulation of slow-burning carbon black/potassium nitrate and fast-burning aluminum/potassium perchlorate were carried out and compared with experimental results to verify the applicability and accuracy of the simulation method. The time differences when the pressure rises to half of the peak pressure (0.5p_m) and reaches the peak pressure (p_m), and the relative errors of p_m were compared and analyzed between the simulation results and the closed bomb test results . Results show that when the pressure of charcoal/potassium rises to 0.5p_m, the time difference between the simulation result and the test result is 0.03 ms, the time difference when reaching p_m is 0.3 ms, and the relative error of p_m is 10%. Correspondingly, the time difference of aluminum/potassium perchlorate at these two conditions is 0.02ms and 0.1ms, and the relative error of p_m is 4%. The p-t curves simulation of pyrotechnic compositions using the deflagration equation of state in MSC.Dytran software has good accuracy and applicability.

Abstract:New energetic materials with molecular perovskite structure (H₂dabco[NH₄(ClO₄)₃](DAP, dabco =N(CH₂CH₂)₃N) were prepared from ammonium perchlorate, 1, 4-diazoxane[2.2.2]octane and perchloricacid, and its crystal structure and morphology were characterized by X-ray diffraction (XRD), fourier transform infrared spectroscopy (FT-IR), scanning electron microscope (SEM) and energy dispersive X-ray spectroscopy(EDS). The thermal decomposition properties of the DAP and AP were studied by thermo gravimetric (TG) and differential scanning calorimetry (DSC). And the hygroscopicity of DAP and AP was measured by weight gain method. Results show that DAP is a new crystal different from AP in structure and morphology. It exhibited the exothermic peak temperature of 385 ℃ and apparent decomposition heat of 3157 J·g^-1.Compared with the AP after the recrystallization, the exothermic peak temperature delayed 19 ℃, apparent decomposition heat increased by 2221.9 J·g^-1. The hygroscopicity of AP is determined to be 0.560%, while the hygroscopicity of (H₂dabco)[NH₄(ClO₄)₃] is only 0.044%, indicating that this method effectively reduce the hygroscopicity of AP.

Abstract:In order to study the catalytic performance of bimetallic oxides in solid propellants, the honeycombs ZnCo₂O₄（ZnCo₂O₄(HCs)） particles grown on nickel foam (NF) were successfully prepared by solvothermal method and the subsequent thermal annealing process. Its phase composition and morphology structure were systematically characterized by X-ray powder diffraction (XRD), X-ray photoelectron spectroscopy (XPS), fourier transform infrared spectroscopic(FT-IR), scanning electron microscopy (SEM) and N₂ adsorption-desorption test. The thermal behavior of ammonium perchlorate (AP) and hexanitrohexaazaisowurtzane (CL-20) catalyzed by ZnCo₂O₄(HCs) were investigated by differential scanning calorimetry (DSC). Results showed that when 20% ZnCo₂O₄(HCs) is added, the thermal decomposition peak temperatures of ZnCo₂O₄(HCs)/AP and ZnCo₂O₄(HCs)/CL-20 decreased most which were 575.01 K and 521.55 K, respectively. Compared with pure AP and CL-20, the exothermic decomposition peak temperatures of ZnCo₂O₄(HCs)/AP and ZnCo₂O₄(HCs)/CL-20 were decreased by 101.87 and 3.73 K and the apparent activation energies calculated by thermal analysis kinetics were reduced by 17.88 and 6.23 kJ·mol^-1. Furthermore, the as-prepared ZnCo₂O₄(HCs) exhibited good catalytic activity comparing with ZnCo₂O₄ nanocrystallites (NCs), nanowires (NWs) and nanospheres (NSs). This can be attributed to the porous structure and large specific surface area of ZnCo₂O₄(HCs), which can provide rich active sites as a catalyst for the thermal decomposition reaction.

Abstract:In order to study the plasticizing properties of new energetic plasticizer (2,2-dinitropyl)-2-hexyl decanoate (A16) with Hydroyl-Terminated Polybutadiene (HTPB), the compatibility of them was simulated by molecular dynamics method. The apparent viscosities and mechanical properties of HTPB/A16 and HTPB/DOS systems at different plasticizing ratios and temperatures were studied and compared. The interaction between HTPB and A16 was dominated by Van der Waals force. The difference between the solubility parameters of HTPB and A16 was only 0.004 (J·cm^-3)^1/2, indicating good compatibility. The apparent viscosity of HTPB/A16 system was higher than that of HTPB/DOS system. With the increasing plasticier mass ratio or temperature, the difference between the two systems decreased. When the plasticizing ratio was 1∶1 and the temperature was 70 ℃, the viscosity of HTPB/A16 was only 60.5 cp higher than that of HTPB/DOS, suggesting equivalent reduction effect of A16 and DOS. Under the same plasticizing ratio, both the tensile strength and elongation of HTPB/A16 system were larger than that of HTPB/DOS system. When the plasticizing ratio was 1∶1, the elongation at break of HTPB/A16 was 18.6% higher than that of HTPB/DOS, whereas the modulus was 8.6% lower.

Abstract:Considering the problem that copper azide (Cu(N₃)₂) has high electrostatic sensitivity and it is difficult to be practically applied, the silicon-based Cu(N₃)₂@carbon nanotubes (CNTs) composite energetic film which can be compatible with Microelectro Mechanical Systems (MEMs) was designed. First, the silicon-based porous alumina film with CNTs grown inside the pores was prepared by a modified two-step anodic oxidation method. Then copper nanoparticles were deposited in the CNTs by electrochemical deposition. The hydrogen azide gas was prepared by reaction between the nitric acid and sodium azide, which reacted with the copper nanoparticles to synthesize Cu(N₃)₂. The morphology, structure and composition of the prepared silicon-based Cu(N₃)₂@CNTs composite energetic films were characterized by field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM) and X-ray diffraction (XRD). Thermal decomposition kinetics of the composite energetic film was studied by differential scanning calorimetry (DSC). Electrostatic sensitivity of the composite energetic film was tested by lifting method. Results show that activation energy of the silicon-based Cu(N₃)₂@CNTs composite film is about 230.00 kJ·mol^-1, while the critical temperature of thermal explosion is about 193.18 ℃ and the 50% ignition energy is about 4.0 mJ. The electrostatic sensitivity of silicon-based Cu(N₃)₂@CNTs composite energetic film is significantly reduced.

Abstract:To study the combustion and energy release characteristics of Zr-based amorphous alloys, the combustion heat of Zr_68.5-xAl_7.5+x(Cu+Ni)₂₄(x=0,2.5,5,7.5) under different oxygen pressures were tested by oxygen bomb calorimetry. The phase composition of combustion products were determined by X-ray diffractometer, and comparative analysis of various energetic materials was conducted. The results show that the combustion heat of Zr-based amorphous alloy is negatively correlated with the Zr∶Al atom ratio. The energy released mainly comes from the oxidation reaction of metal elements, and a very small amount of energy comes from the chemical reaction between metal elements. The combustion heat and reaction efficiency increase with the increase of oxygen pressure, according with the first-order decay index function. Zr-based amorphous alloy has higher chemical potentiality, compared with PTFE/Al and TNT, Its specific energy per unit mass is 10.981 kJ·g^-1，and the specific energy per unit volume is 72.035 kJ·cm^-3.

Abstract:The main purpose of this paper is to experimentally determine the all-fire shock initiation criterion of Hexanitrostilbene-Ⅳ(HNS-Ⅳ) explosive under the impact of a short-duration high pressure pulse. Up-down tests of three kinds of polyimide flyers with different thicknesses (12.5, 40 μm and 50 μm) were carried out using Exploding Foil Initiation system (EFIs) in order to determine the minimum all-fire charging voltage. Using Photon Doppler Velocimetry (PDV) technology, the impact velocity of the three flyers under their minimum all-fire conditions was obtained. On this basis, the interface pressure p, particle velocity u and duration τ of the three kind of flyers impacting onto HNS-Ⅳ explosive were calculated based on shock wave theory and dynamic simulation. Furthermore, the all-fire shock initiation criterion of HNS-Ⅳ explosive under the impact of short-duration high pressure pulse was finally determined by data fitting. Results show that the all-fire pⁿτ criterion for HNS-Ⅳ with charge density of 1.56 g·cm^-3 explosive is p^2.88τ≥7.21 in the range of 10-13 GPa and 4.0-8.7 ns.

Abstract:The interface structure has an important influence on the mechanical properties, safety properties, and thermal stability of energetic materials. Polydopamine (PDA) is a surface chemistry that can functionalize surfaces of most materials. PDA has the advantages of simple preparation, easy control, mild reaction, safe operation and further functionalization. In recent years, bioinspired PDA has been wildly applied in energetic materials. In this paper, the influences of the bioinspired controllable interface constructed by PDA on the structure and properties of energetic materials are reviewed. Firstly, the bonding mechanism of PDA is introduced. Secondly, the surface functionalization method of PDA for energetic materials and functional fillers are summarized. Thirdly, the influences of surface modification with PDA on the safety, thermal stability, mechanical properties, and thermal conductivity of explosives are mainly described. Then, the unique advantages of PDA in the structural design and performance control of energetic materials and the existing problems are pointed out.At last, four key research directions are stated: further exploration of the mechanism of interfacial interaction between PDA and energetic materials or binders, design of regular and controllable interface structure, introduction of functional polymers, as well as expansion of surface functional materials for energetic materials.

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