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Abstract:Conventional methods for evaluating aging effects of solid propellants stored at natural temperature need long-term (at least 10 years) and detailed (at least daily) environment temperature data. It is very difficult or expensive to access those data in storage places. Even if the data has been obtained, it would be a very heavy workload to process them. A novel method has been established to substitute the conventional methods limited by data acquisition and processing. The method is based on monthly average temperature data. According to seasonal and diurnal variation models of natural temperature, the parameters of these models have been calculated from monthly average temperature data and local climate characteristics. Therefore, the aging equivalent temperature could be evaluated, and the natural temperature aging effects could be predicated. This method is simpler than conventional method in data processing. And the required temperature data of the method can be easily obtained through public ways. Aging equivalent temperatures of three typical solid propellants （(hydroxyl-terminated polybutadiene(HTPB）, nitrate ester plasticized polyether (NEPE）, composite modified double-base（CMDB)） stored in four typical regions was calculated by the novel method. Results show that the aging equivalent temperature is much higher than the annual average temperature. The difference between the aging equivalent temperature and the annual average temperature increases with the increase of the annual temperature range. As the aging activation energy of solid propellant increases, the aging equivalent temperature approaches the maximum monthly average temperature, and the difference between the equivalent temperature and the annual average temperature becomes larger.

Abstract:The influence of diphenylamine (DPA) on the thermal stability of nitrocellulose (NC) was investigated by isothermal decomposition kinetics. Pressure versus time curves of the gas generated by the thermal decomposition of NC/DPA (3%) mixed sample at 378.15-398.15 K were obtained by using the isothermal decomposition gas metering device. There is a visible inflection point in this curve. The thermal decomposition kinetic parameters of NC/DPA (3%) composite were calculated by Arrhenius equation and model-fitting method. The storage life of NC and NC/DPA composite was estimated using Berthelot equation. The results show that the activation energy of NC/DPA (3%) before the inflection point is 164.6 kJ·mol^-1, and the activation energy of NC/DPA (3%) mixed sample after the inflection point is 150.4 kJ·mol^-1. Compared with the NC raw material, the activation energy of NC/DPA (3%) before the inflection point is increased by 17.7 kJ·mol^-1. With a decomposition extent of 0.1% as the criterion, the storage life of NC/DPA (3%) at room temperature is 18.3 years, indicating that the storage life of NC can be extended by 7.7 years after the addition of 3%DPA.

Abstract:Aiming at the criterion of evaluating the shelf life of explosives by Bourdon method, the decomposition depths of 0.05% and 0.1% were used as the end points of life. The comparison results of storage life of 32 kinds of explosives at 25-50 ℃ were obtained by linear regression based on Berthelot equation. Two cases were found: 1) For most explosives, the estimated storage life at the same temperature that obtained by taking 0.05% decomposition depth as the end point was less than the estimated shelf life that obtained by taking 0.1% decomposition depth as the end point, but sometimes the estimated shelf life by the former would be extremely short; 2) For very few explosives, the estimated shelf life with 0.05% decomposition depth as the end point was greater than the estimated shelf life estimated at 0.1% decomposition depth at room temperature. However, as the temperature increased, the shelf life estimated by the 0.05% decomposition depth was again less than the estimated shelf life of 0.1% decomposition depth. Whether the selected experimental data points at each temperature are in the isokinetic decomposition period of the explosive is the reason for the difference. Results show that it is more scientific to use the decomposition depth of explosives in the isokinetic decomposition period as the end point criterion for evaluating the shelf life by Bourdon method.

Abstract:Life-extension of missile is a systematic project with both military and economic benefits. As the domestic test on storage and life-extension is not scientific and systematic, it affects the effectiveness and efficiency of missile life-extension. This paper expounded the fundamental connotation of missile storage and life-extension test, summarized the main difficulties in storage and life-extension test, and proposed the basic flow of missile storage and life-extension test. The storage and life-extension test was divided into four parts: natural storage test, life extension test, accelerated storage test and validation test. The main research contents and research progress of each part were analyzed, and the key technologies such as storage life prediction based on natural storage test data, failure mechanism analysis and residual life prediction, overall planning for life-extension technical scheme, and accelerated storage test design based on actual service environment were summarized. Finally, the development trend and key research directions of storage and life-extension test technology were discussed. It has certain academic value and engineering guiding significance for promoting the technology development of missile storage and life-extension test.

Abstract:Low-field nuclear magnetic resonance (LF-NMR) technology has the advantages of fast, nondestructive, continuous and accurate, which has attracted attention in the fields of cross-linking density, curing process monitoring and aging property evaluation of explosives and propellants. The basic principle of LF-NMR was introduced. The application of LF-NMR in the curing monitoring of composite solid propellants, cross-linking aging assessment of composite solid propellants and polymer bonded explosive(PBX), and aging property evaluation of new type fuel air explosives (new-type FAE) was summarized. It was proposed that the application of LF-NMR in the aging performance monitoring of explosives and propellants should be further studied, the problems of classification monitoring of different ¹H relaxation characteristics and establishment of correlation equations between relaxation characteristic parameters and key parameters of mechanical properties should be solved, and the application of key parameters——transverse relaxation time (T₂) of LF-NMR in the aging performance evaluation of explosives and propellants should be strengthened.

Abstract:1,4-Diamino-3,6-dinitropyrazolo[4,3-c]pyrazole(DADNP) was synthesized by N-amination reaction, and its structure was characterized by NMR, IR, MS and element analysis. The thermal decomposition kinetics and mechanism were studied by means of different heating rate differential scanning calorimetry(DSC), rapid-scan fourier transform infrared spectroscopy(RSFTIR) and thermogravimetry-mass spectrometer(TG-MS) coupling technique. The results show that the apparent activation energy and pre-exponential constant of the exothermic decomposition reaction of DADNP obtained by Kissinger method are 166.45 kJ·mol^-1, 1016.53 s^-1. The decomposition of DADNP includes two stages, which begins with the rupture of C─NO₂ with subsequent loss of NO₂ under electron impact and heating condition, respectively. In the first stage of decomposition, the rupture of one C─NO₂ and one pyrazole ring in DADNP molecule with the release of NO₂ and N₂H₂ occur under electron impact condition, whereas the homolysis of two C─NO₂ bonds occur with the loss of two molecular NO₂ under heating condition.

Abstract:Asymmetric triazole nitrogen-rich energetic compound 3-amino-3"-nitroamino-5,5"-bis-1H-1,2,4-triazole （3）was synthesized using 3-amino-1H-1,2,4-triazole-5carboxylic acid as raw material for the first time, and the product structure was characterized by IR, NMR and MS. Its thermal stability and decomposition process were studied by differential scanning calorimeter (DSC) combined with thermogravimetric analysis(TG). The results show that the decomposition temperature of compound 3 is as high as 160 ℃. The standard molar enthalpy of combustion (Δ_CH^θ_m) measured by an oxygen bomb calorimeter is -1952.25 kJ·mol^-1. The standard molar enthalpy of formation (Δ_fH^θ_m⁾ calculated and obtained according to Hess"s law is -336.245 kJ·mol^-1. The powder density measured by powder densitometer is 1.6137 g·cm^-3. The detonation pressure and detonation velocity predicted by EXPLO 5 program are 9.6 GPa and 5745.5 m·s^-1, respectively. The impact and friction sensitivities of this compound are 80 J and 360 N, respectively, which shows that this compound is a new type of insensitive energetic material.

Abstract:The intermediate ethyl nitramine (ENA) and the final product 3,5-dinitro-3,5-diazaheptane (DNDA7) were syntheized starting from 1,3-diethylurea via the reactions of nitration, hydrolysis and condensation. The yield and purity of ENA is 80.6% and 99.3% while 67.7% and 99.0% for DNDA7, respectively, the overall yield is 54.6%. The structure of DNDA7 was characterized by IR, NMR and elemental analyses. Meanwhile, the reaction conditions for nitration, hydrolysis and condensation were optimized as follows: 20% fuming sulphuric acid and nitric acid were used as the nitrating agents, and the recation temperature was controlled between -5 ℃ to 0 ℃ for nitration reaction; while the hydrolysis reaction was finished in 30 min at 20 ℃; and the molar ratio of ENA and paraformaldehyde is 1∶0.5, the reaction mixture was stirred at 23-25 ℃ for 30 min for condensation reaction. The thermal decomposition properties of DNDA7 and its compatibility with normal energetic materials were studied by using differential scanning calorimetry(DSC). The melting point and thermal decomposition temperature of DNDA7 is determined to be 77.3 ℃ and 260.8 ℃, respectively. DNDA7 performs good compatibility with RDX, basic compatibility with HMX, NQ and GAP, and poor compatibility with NC and FOX-7. Moreover, the mechanical sensitivities of DNDA7 were tested according to the national standard GJB772A-1997, and it isfound that the impact sensitivity is H₅₀>125.9 cm and the friction sensitivity is 4%.

Abstract:With diethylene glycol (DEG) and triethylene glycol (TEG) as starting materials, novel energetic plasticizers 1,5-diazido-3-oxopentane (AZDEGDN) and 1,8-diazido-3,6-dioxooctane (AZTEGDN) were synthesized via nitration and azidation reaction. The conditions of azidation reaction were optimized. And the structures were characterized by infrared spectra, magnetic resonance spectra and element analysis. Results show that the optimal reaction conditions for the synthesis of AZDEGDN are the molar ratio of sodium azide and DEGDN of 2.7∶1, the reaction temperature of 80 ℃,and the reaction time of 8 h, under which the yield of AZDEGDN is 96.4% and the purity is 99.1%.The optimal reaction conditions for the synthesis of AZTEGDN are the molar ratio of sodium azide and TEGDN of 2.5∶1, the reaction temperature of 75 ℃, and the reaction time of 8 h, under which the yield of AZTEGDN is 96% and the purity is 99.2%. In addition, the enthalpy of formation, the decomposition temperature, the friction sensitivity and impact sensitivity of AZDEGDN are 912.5 kJ·mol^-1, 249.3 ℃, 0% and 64.6 cm, respectively; while the main properties of AZTEGDN are 898.1 kJ·mol^-1, 256.1 ℃, 0% and 151.4 cm, respectively. However, both of their glass transition temperatures are less than -100 ℃.

Abstract:In order to investigate the process and kinetics for the thermal oxidation of micron zirconium powders, the particle size distribution, micromorphology, elemental content and phase characteristics of the zirconium powders were studied by laser particle size analysis, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The oxidation process at different heating rates was studied by thermogravimetry and differential scanning calorimetry (TG-DSC ). The kinetic parameters and reaction model were obtained. The particle size of zirconium powders was in the range of 15-46 μm, with irregular particles. The main phase of zirconium powder particles was metallic Zr. The oxidation process of zirconium powder can be divided into the four stages including initial oxidation, accelerated oxidation, vigorous oxidation and reaction equilibrium. The non-isothermal oxidation process followed the random nucleation and subsequent growth model function with the integral expression . Further, the activation energy E_a and pre-exponential factor A for the thermal oxidation reaction was 175.83 kJ·mol^-1 and 1.91×108 s^-1, respectively. The reaction rate constant k=1.91×10⁸ exp (-2.1×10⁴/T).

Abstract:The aim of the paper is to investigate the evolution law of burning in high explosive (HE) cracks under confinement, obtain the characteristics of convective burning in typical explosive cracks, and deepen our mechanism understanding on the process for high intensity reaction of projectile fillings under accidental ignition. The propagation of burning in preformed cracks inside octogen(HMX)-based polymer bonded explosive (PBX)(with a content of 95% for HMX) under thermal initiation was recorded by high-speed camera and pressure transducers. It is found that convective burning in 50 μm wide crack of HE under confinement can produce high pressure exceeding 250 MPa with the burning wave speed exceeding 400 m·s^-1. Comparison between crack widths reveals that with the increase of crack width, the peak pressure attributed to convective burning decreases but the burning wave speed increases. Detailed analysis of experimental data reveals that there are four stages in the evolution of convective burning in explosive cracks. The first stage is the early stage transportation of initial reaction products through crack under relatively low pressure gradient without burning on HE surface. The second stage is the steady convection of product gases with pressure growing due to combustion inside crack. The third stage is the rapid pressurization due to violent burning of HE with fracture of HE and deformation of the confinement shell. The fourth stage is the confinement failure process under extremely high pressure.

Abstract:To study the influence of wide temperature range on the detonation wave front curvature rate for insensitive explosives, pseudo-steady-state detonation wave velocities and wave front shapes were obtained for JB-9014 with three different grain diameters（10，15，30 mm）at the temperature -55, 11 ℃ and 70 ℃ by using high speed streak camera technique and electric pins velocimetry. Results show that at the same temperature, the pseudo-steady-state detonation wave velocity is concave down for small-diameter grain but it is concave up for large-diameter grain. At the same grain diameter, the velocity of pseudo-steady-state detonation wave velocities of JB-9014 decreases linearly as the ambient temperature increases and the decrease of slope is related to the diameter of the grain. When the variation of detonation wave velocity of JB-9014 with grain diameter and ambient temperature is fitted by polynomial, the fitting results are in good agreement with the experimental data. For JB-9014 with three kinds of grain diameters, the pseudo-steady-state detonation wave front shape becomes flatter with the increase of the ambient temperature. When the experimental results of three kinds of grain diameters are fitted by genetic arithmetic method, the D_n(κ) parameters of JB-9014 over a wide temperature range are obtained. When the local curvature is less than 0.16, the D_n(κ) relation decrease with the increase of temperature, while the result is the opposite when the local curvature is greater than 0.26. When the detonation shock dynamics (DSD) method is used to calculate the non-ideal propagation process of detonation wave of grains with three kinds of diameters, the calculated results are in good agreement with the experimental values.

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