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Abstract:In order to improve the combustion performance of aluminum powder in the solid propellants, the aluminum matrix composite was prepared by high energy ball milling with aluminum powder as matrix and FeF₃ as additive. The effects of powder ratio and milling parameters on the micromorphology, structure and thermal properties of aluminum matrix composites were studied. The micron grade aluminum matrix composites were prepared by optimized process. TG-DSC analysis showed that Al-FeF₃ composite can realize fast oxidation at lower temperature (600-1400 ℃) in the oxidation process. The end-fired 75 engine test demonstrated that no large molten aluminum powder residue was observed in the engine shell after replacing spherical Al with Al-FeF₃ composite. The residue rate was decreased from 6.151% to 4.215%, indicating enhanced combustion efficiency for the Al-FeF₃ composite. Therefore, Al-FeF₃ composite has potential application value in reducing combustion residue rate of solid propellant and two-phase flow loss of engine.

Abstract:In order to understand the effect of nanometer nickel(nano-Ni) on the over-all performances of Al-composite modified double base propellant(CMDB) and hexogen(RDX)/Al-CMDB propellants, the energetic property, thermal stability, mechanical sensitivity, mechanical performances, inner ballistic properties and the dependence of burn rate on the aging process have been studied. The results show that the addition of nano-Ni had little effect on the performances. The effects of nano-Ni on combustion behavior of these propellants have also been studied. The results show that nano-Ni can greatly improve the combustion performances. The inclusion of nano-Ni can increase the burn rate of Al-CMDB propellant from 28.32 mm·s^-1 to 35.94 mm·s^-1 at 9.81 MPa, and lowering the pressure exponent(n) between 12-22 MPa from 0.26 to 0.12. The burn rate of RDX/Al-CMDB containing nano-Ni at 9.81 MPa can reach 36.63 mm·s^-1, with negative n between 16-22 MPa at different initial temperature. The specific impulse of RDX/Al-CMDB propellant could reach 241.1 s at -40 ℃ and 246.9 s at 50 ℃ in Φ130 mm rocket motor.

Abstract:The slow cook-off and fast cook-off tests of hydroxyl terminated polyether（HTPE） propellant have been carried out as a function of sizes of samples (3 types). The temperature distribution inside the samples during the tests has been analyzed by Fluent software. The results show that during the slow cook-of tests, there are few differences in the response temperature of the samples. If the response degree of slow cook-off tests increases significantly, the corresponding fast cook-off test increases slightly. The response levels for slow cook-off tests of HTPE propellants at small-scale, medium-scale and large-scale sample are combustion, explosion and detonation, respectively. In comparsion, the corresponding response levels from the fast cook-off tests are combustion, combustion and deflagration, respectively. In the slow cook-off simulation, the ignition points of the three different size samples are all the same at the center of the propellants. In the fast cook-off simulation, the ignition point locations of small and medium sample are in the annular region of the angle between the propellant and cap, whereas there are multiple ignition points in the large sample located in the middle of the case. In the experimental study of the cook-off characteristics of solid rocket motor, the effect of the grain structure and sample size on heat transfer mechanism must be fully considered in the rational design of small-scale analog motor.

Abstract:In order to realize the reliable ignition and clarify combustion control mechanism of hydroxylamine nitrate (HAN)-based electrically controlled solid propellant (ECSP), thermogravimetric-differential scanning calorimetry-mass spectrometry (TG-DSC-MS) and impedance-frequency scanning techniques have been used. The effects of thermal decomposition behavior, decomposition products, pressure and temperature on conductivity of ECSP were studied independently. The results showed that compared with the pure HAN solution, the thermal stability of ECSP was improved. The initial decomposition temperature was raised by 11 ℃, whereas the peak temperature of exothermic peak was decreased by 24 ℃ with a broader exothermic temperature range. Combining the thermal decomposition behavior of ECSP with the mass spectrometry curves of the gaseous products, it could be concluded that the thermal decomposition process of HAN-based ECSP might be divided into three steps: the thermal decomposition reaction of HAN, the interaction of the thermal decomposition products of HAN and the undecomposed HAN with polyvinyl alcohol (PVA), and the thermal decomposition of the residue components in ECSP. The electron conductivity of the ECSP was increased largely in the low frequency range (0-1000 Hz), but tended to be constant in the high frequency range (greater than 1000 Hz) as the frequency increased. With the increase of the pressure and temperature, the electron conductivity of the ECSP was increased. By raising the temperature to 150 ℃, the electron conductivity in the high frequency range was reduced by 2.92% compared with that obtained at 125 ℃.

Abstract:Several novel GO-based bis-tetrazole energetic coordination polymers (ECPs) were designed and prepared by solvothermal method, which contain cobalt(Ⅱ) and nickel(Ⅱ) as coordination center, 5,5′-bis-tetrazole(H₂BT) and 5,5-bis-tetrazole-1,1-dioldehydrate (DHBT) as ligand. The coordination polymer crystal can be controlled through regulating the experimental conditions. Five typical promising catalysts of GO-Co-DBT、 GO-Co-BT、GO-Ni-DBT、α-GO-Ni-BT and β-GO-Ni-BT were characterized by XRD(X-ray diffraction), XPS(X-ray photoelectron spectroscopy), SEM(scanning electron microscope)/EDS(Energy Dispersive Spectrometer) and DSC(differential scanning calorimetry)-TG(Thermogravimetric Analysis) techniques. DSC-TG results of GO-Co-DBT、GO-Co-BT、GO-Ni-DBT、α-GO-Ni-BT indicate that GO-based bis-tetrazole energetic coordination polymers could reduce crystal defect, then lower the hot pot and improve thermostability, so the dicomposition temperatures of GO-Co-DBT, GO-Ni-DBT and GO-Ni-BT are all above 200 ℃. These ECPs as energetic catalysts have significant catalytic effect on thermal decomposition of AP and RDX. The reason can be that more O elements being transferred to react with NH₄⁺ results in increasing the yields of NH₃ and H₂O, which also made two decomposition peaks of AP overlap and the whole heat release increase. The heat releases of AP and RDX catalyzed by graphene-templated bis-tetrazoles are 2757.0 J·g^-1 and 2898.0 J·g^-1 respectively, which improve more than 50% compared with pure AP and RDX. The endothermic peak of AP corresponding to the crystal transformation is also reduced to 23.2 kJ·mol^-1. Prepared GO-based bis-tetrazole energetic coordination polymers could enhance thermostability and decomposition efficiency of AP and RDX.

Abstract:To study the agglomeration behaviors and agglomeration characteristics of aluminum particles in aluminum-magnesium (Al-Mg) oxygen-poor propellant, the combustion process of Al-Mg oxygen-poor propellants and the microstructure and particle size of agglomeration products of Al particles were investigated by using scanning electron microscopy and optical visualization experiment method. A model for predicting the aluminum agglomeration size was established and fitted to the experimental data. Results show that the secondary agglomeration occurs after the agglomerate of aluminum droplet formed on the combustion surface is separated from the combustion surface. At 1.0 MPa, the propellant specimens burns sufficiently, the aluminum particles after burning become smooth spherical alumina particles and the magnesium particles after burning become white flocculent magnesia. At 0.2 MPa, the propellant specimens burns insufficiently, the aluminum particles are not completely oxidized and the surface is rough. With the increase of combustion chamber pressure, the volume average particle size D(4,3) of aluminum agglomerate decreases, while the surface area average size D(3,2) increases, and particle size distribution tends to single peak, indicating that with the increase of pressure, the closer the values of D(4,3) and D(3,2) are, the more regular the shape of aluminum agglomerate is, and the more concentrated the agglomeration size distribution is. The agglomerate size is inversely proportional to the burning rate.

Abstract:Solubility, metastable zone width and induction period are important parameters in the crystallization process of ammonium dinitramide(ADN). The solubilities of ADN in n-butanol, isopropanol and mixed solvent of water and isopropanol (volume ratio as 1∶10 and 1∶6) were measured by dynamic method and the solubility data were fitted by Apelblat equation and λh equation, respectively. The effects of stirring speed and cooling rate on the metastable zone width of ADN in n-butanol and isopropanol and the effects of different supersaturation on the induction period were investigated, respectively. Results show that the Apelblat equation and the λh equation can well fit the solubility of ADN. With the decrease of the cooling rate and the increase of the stirring speed, the width of the crystalline metastable zone narrows. The crystallization induction period shortens with the increase of supersaturation. Using the self-consistent Nývlt equation and 3D nucleation theory, combined with the metastable zone width and induction period data, the nucleation order m is calculated to be about 4, and the solid-liquid interfacial tension of ADN in n-butanol and isopropanol are 0.235 mJ·m^-2 and 0.191 mJ·m^-2 for homogeneous nucleation, 0.070 mJ·m^-2 and 0.067 mJ·m^-2 for heterogeneous nucleation, respectively.

Abstract:An experimental platform was designed for the explosive dispersion process of short carbon fibers. According to the characteristics and requirements of explosive dispersion for different periods, two high-speed cameras were used to record the fracture process of the shell and the macro-expansion process of the cloud using the frame rates of 50,000 frames per second and 2000 frames per second respectively. By measuring and analyzing the sequence images of the whole process of explosive dispersion, the characteristics of shell fracture and cloud dispersion formation were obtained, and the curves of the diameter, height and expansion velocity of explosive dispersion cloud with time were established. Analysis of the high speed video records of the explosive dispersion of four kinds of projectiles with a similar structure and identical loading parameters show that, the explosive dispersion process of short cut carbon fibers mainly goes through four stages: shell rupture, jet ejection, cloud expansion and turbulent mixing. The dispersion process follows similar laws that, the initial cloud diameter has a linear relationship with the bomb diameter and the cube root of the loading mass of fibers respectively, and the initial cloud height has a quadratic polynomial relationship with the bomb height.

Abstract:A kind of non-primary explosive percussion primers were made with the non-primary explosive charge composed of 50% （mass fraction）of 50 nm-sized Ti and 50%（mass fraction） of 5 μm-sized KClO₄. The output characteristics of the non-primary explosive percussion primer were studied by means of simulation experiment and high-speed photography. The experimental results show that when a firing pin with diameter of 1.0 mm hits the primer, the reaction form of drug in the primer is slow combustion. When a firing pin with diameter of 1.7 mm hits the primer, the reaction form of drug in the primer is deflagration. When a firing pin with diameter of 3.0 mm hits the primer, the reaction form of drug in the primer is explosion. When reacting in the form of slow combustion, the output flame intensity of the primer is very weak, the hot ash is 0, and the 50% characteristic ignition distance is 0. When reacting in the form of deflagration, the flame duration of the primer output is about 250 μs, the hot ash is 12.9 mg, and the 50% characteristic ignition distance is 94 mm. When reacting in the form of explosion, the flame duration of the primer output is about 50 μs, the hot ash is 7.7 mg, and the 50% characteristic ignition distance is 52 mm, whereas for the primary explosive charge composed of lead azide, 50 nm Ti and 5 μm KClO₄ in the same formula series, there is only one type of reaction form-explosion, the flame duration of the primer output is about 50 μs, the hot ash is 6.5 mg, and the 50% characteristic ignition distance is 32 mm. When the percussion primers without primary explosive is ignited in the form of deflagration, its ignition performance is better than that of the percussion primers with primary explosive in the same formula series.

Abstract:To study the change rule of transverse relaxation characteristics and cross-linking density of hydroxyl-terminated polybutadiene(HTPB) liner under the condition of constant strain storage aging, accelerated aging tests of HTPB liner at 0%, 5%, 10% and 15% constant strain levels were designed. The proton transverse relaxation decay curves of HTPB liner were measured by the low-field ¹H NMR CPMG sequence and the cross-linking density of HTPB liner was calculated and obtained based on the modified single chain model. The change rule of cross-linking density was analyzed. At the same time, a cross-linking density aging model considering physical stretching and chemical aging factors was established and the influence factors and changing rule of the parameters of aging model were studied. The results show that the cross-linking density of HTPB liner shows a trend of increasing firstly and then decreasing under the condition of constant strain storage aging. The existence of constant strain causes an increase of the stress relaxation time of HTPB liner, but it has no significant effect on the aging reaction rate constant of HTPB liner. The specific form of established cross-linking density aging model is . The correlation coefficient R is more than 0.9500 (R>0.9000 at 5% constant strain) between the model and the experimental results, which can be used to describe the aging law of crosslink density of HTPB liner under constant strain conditions.

Abstract:Considering the safety problems of energetic additives and “pressure desensitization” in the engineering application of traditional emulsion explosives, hollow energetic microcapsules and hollow pressure-resistant microcapsules were developed.Hollow energetic microcapsules integrated the functions of energetic additives and sensitizers, while hollow pressure-resistant microcapsules had the functions of “self-sensitization” and “chemical sensitization”. The microstructures of hollow energetic microcapsules and hollow pressure-resistant microcapsules were characterized by scanning electron microscopy, optical microscope and laser particle size distribution analyzer. The thermal, detonation and storage stability properties of hollow energetic microcapsules sensitized emulsion explosive were characterized by thermal analysis test, explosion performance experiments and compatibility tests, respectively. The regeneration of sensitized bubbles was verified by observing compressed hollow pressure-resistant microcapsules under an optical microscopy. Results show that the hollow energetic microcapsules and hollow pressure-resistant microcapsules with spherical morphology, uniform particle size distribution, and hollow energetic microcapsules could significantly improve the detonation performance of emulsion explosive without affecting its safety and storage stability. The brisance and detonation speed of the hollow energetic microcapsules sensitized emulsion explosive are 23.20 mm and 4797 m·s^-1 ,respectively. After collapse of the hollow pressure-resistant microcapsule under external pressure, the inner and outer substances will react and generate new sensitized bubbles, which avoids the pressure desensitization of emulsion explosive. Hollow functional microcapsules can effectively solve the problems of traditional additives by integrating the characteristics of sensitizers and functional additives.

Abstract:Using ethyl 2-(3-(dinitromethyl)-1H-1,2,4-triazol-5-yl)acetate as a starting material, diguanylurea 3,5-bis(dinitromethyl)-1,2,4-triazolate (DMDNMT) was firstly designed and synthesized via the reactions of nitration, hydrolysis and metathesis. The structures of all compounds were characterized by ¹H NMR, ¹³C NMR, IR and element analysis. Based on the theoretical values of densities and heat of formation, the detonation parameters were calculated using Gaussian 09 program and EXPLO5 6.04. Results show that the density of DMDNMT is 1.81 g·cm^-3, the heat of formation is -446.1 kJ·mol^-1, the detonation velocity and detonation pressure are 8624.8 m·s^-1 and 29.2 GPa, respectively. DSC and TG-DTG measurements indicate that the decomposition temperature of DMDNMT is 177.3 ℃, and its impact sensitivity determined by standard BAM method is 24 J.

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