Abstract:In this specific issue,9 papers addressed the various issues of reduced sensitivity explosive crystals preparation,characterization,properties and performance in China.

Abstract:In order to investigate the fluctuation phenomena of RDX crystalline particles subject to pressing,the compression stiffness tests (CST) were conducted for five types RDX crystalline particle ensembles from three sources and it is found that the fluctuation of the compression relates closely to the coherence strength of single particle of RDX. The measured fluctuation amplitudes of recrystallized is about 2.4 MPa,which is much higher than that of commonly used RDX,namely 1.2 MPa,and D-RDX bears the highest fluctuation amplitude of 4.4 MPa,it means that recrystallized RDX (D-RDX) has a maximum allowable failure stress and its quality has been well improved compared to the rest of the samples. This study shows that when using CST to evaluate the quality,the fluctuation should be considered carefully.

Abstract:Effects of RDX crystal characteristics including crystal internal porosity,particle size and distribution on shock sensitivities were studied by applying a method that RDX particles immersed in rap oil which excluded effects on shock sensitivity of binder/crystal interface,binder porosity and crystal shape. The shock initiation threshold of RDX/rap oil (mass ratio 76/24) compostion was determind with gap test where RDX was recrystallized to various qualities. Results show that the gap thickness decreases from 14.0 mm to 12.2 mm when the crystal apparent density increases from 1.7961 g·cm^-3 to 1.7983 g·cm^-3,and gap thickness decreases from 13.5 mm to 12.3 mm with increasing of particle size at the range of 50-600 μm,and this shows that crystal apparent density and particle size are two important factors affecting shock sensitivity. Impact sensitivity of RDX powder by drop weight apparatus was also studied. The test shows that drop weight impact sensitivity decreases from 75 cm to 35.8 cm evidently when particle average size increases from 16.7 μm to 337.9 μm,and does not almost vary while crystal apparent density changing at 1.7961-1.7983 g·cm^-3,which demonstrates that particle size is the important factor affecting impact sensitivity.

Abstract:The micro-structure of RDX was analyzed by small angle X-ray scattering (SAXS). The amount,scale and size distribution of pores in RDX were obtained by SAXS analysis. Results show that the magnitude of pores in the RDX samples decrease with increasing of the scales of RDX. Compared to the sample (<180 μm),the pores of the sample (>420 μm) decrease to about only a half. But the characteristic dimension of pores seems only have 1-2 nm difference. The Porod analysis of RDX shows that there are not only micro-voids but also cracks structure in the RDX.

Abstract:By using Hopkinson principle and impact sensitivity test method,an impact safety experiment was designed for studying the impact security diversity between PBX-based RDX and PBX-based reduced insensitive RDX（D-RDX） explosive,which can determine the dynamic change process and the impact sensitivity of explosive sample in the higher impact velocity. Results show that the impact safety of PBX-based RDX and PBX-based D-RDX explosive,the reflecting amplitude and pulse width after impact loading are quite different. The result of LS-DYNA numerical simulation are basically consistent with experimental results.

Abstract:Crystallization behavior of RDX in different solvents was investigated,and cyclohexanone was founded to contribute the highest crystal quality. An in-depth study involved the cooling crystallization of RDX from cyclohexanone was conducted. Results show that stirring speed affects the particle size and its distribution mainly,while the cooling rate determines the number and size of internal defects,when the stirring speed is in 200-400 rpm and the cooling rate in 0.05-0.2 K·min^-1,the characteristic drop height of RDX can increase by 70%.

Abstract:HMX with round and smooth crystal particles was prepared by improving solvent etching,and was compared with raw HMX. Their particle sizes and morphologies were characterized with optical microscopy (OMS),scan electron microscope (SEM) and laser particle size analyzer,and packing densities were tested by standard vessel method,and thermal and mechanical properties were tested by differential scanning calorimeter (DSC) and the compressive stiffness test (CST). Results show that rounded HMX is round and smooth,the characteristics such as the powder size distributions,thermal properties and mechanical sensitivity do not change,while packing density is increased by 13% and mechanical properties are obviously improved.

Abstract:Coefficient of thermal expansion (CTE) and theoretical density of explosive crystal are significant properties, which affect the performance of explosives largely. XRay powder diffraction (XRD) is an important method to measure the CTE and theoretical density of explosives. The methods and principles for measuring the two parameters by XRD were described,and the experimental results of RDX and HMX explosive crystals obtained by density gradient method verified the reliability and accuracy of the method. It is proposed that the application of Xray diffraction should be strengthened in research of explosive crystal.

Abstract:The microscopic structures of typical crystal explosives (HMX and RDX) were studied including single crystals and loose stacked crystal particles with microfocus X-ray industrial volume computed tomography (μCT). The structure information has been obtained such as nice appearance,intragranular cavities and density distribution. Results show that the high quality crystal has clear edges and corners,the crystal surface is smooth and the interior density is homogeneous but many tiny cavities in it. The surface is rough and the edges and corners are not clear for the low quality of HMX and RDX. Furthermore,the number of interior cavities is big and the density is not well-distributed and high density localities usually exist. The statistical results indicate that the cavity ratio and quantities decrease for recrystallized RDX(D-RDX) to normal RDX(N-RDX) and the less the cavities the more the amount to some degree but very small in the cavity ratio,and illustrate that level cavities greater than micron are important factor for crystal density and other performance.

Abstract:A kind of desensitized octogen (D-HMX) was characterized with various analysis methods, including Optical Microscopy with Matching Refractive Index(OPM), Scanning Electron Microscopy(SEM), Laser Particle Sizer, High Performance Liquid Chromatography (HPLC), density gradient technique and X-ray Diffraction(XRD). The thermal properties of D-HMX were investigated by Differential Scanning Calorimetry (DSC) and Vacuum Thermal Stability test(VST). The sensitivities of D-HMX against friction, impact and shock were studied. Compared with conventional octogen (C-HMX), D-HMX has better morphology, lesser crystal defects, better thermal properties and takes great effect on reducing shock sensitivity in both cast and pressed PBX formulations. Which are incarnated from the following aspects. First, the D-HMX has no twinned crystals or congeries, which shape is regular polyhedron and nearly spheric. Second, there are no inclusions in D-HMX crystals, the purity of D-HMX is (99.6±0.1)% and the mean particle density is great 1.9016 g?cm^-3. Third, the results of DSC and VST show that the β→δ phase transition of D-HMX is shifted to high temperatures about 6 ℃ and that the amount of gas evolution of D-HMX is obviously less after being heated for 48 h at 120 ℃ compared with C-HMX. Fourth, the results of shock sensitivities demonstrate that the aluminium gap thicknesses of cast and pressed PBXs based on D-HMX are lesser 10%~23% than that of PBXs based on C-HMX. Additional, the impact sensitivity of D-HMX appears lower sensitivity than C-HMX. Especially for the fine grain D-HMX(FD-HMX), the drop-height of 72.2 cm and initiation probabilities of 24% indicate there are significantly higher resistance to impact than the fine grain C-HMX(FC-HMX) of 16.8 cm and 88%.

Abstract:Porous silicon was prepared by electrochemical etching on silicon wafer with micro-electromechanical systems(MEMS). The structure of porous silicon and porous silicon explosive was characterized by scanning electron microscopy(SEM),Micromeritics ASAP 2020,differential scanning calorimetry (DSC) and Fourier transform infrared spetroscopy （FTIR),and the ignition properties of porous silicon explosives were studied as well. Results show that porous silicon has a sponge-like structure with nano-pore sizes,about 20 nm and larger specific surface area,and porous silicon explosive reacts at 515 ℃,and can be ignited with heat stimulation energy by baking 2 min and 1.6 A current,which shows that under no restrict condition, porous silicon explosive can be ignited by heat and eletricity energy.

Abstract:The porous silicon was prepared by electrochemical etching and it was filled ammonium perchlorate or sodium perchlorate with in-situ method in order to get porous silicon energetic chips. Results show that the thickness of porous silicon layer is 90-100 μm,and these porous silicon layers endure the ultrasonic waves when porous silicon layers are filled ammonium perchlorate or sodium perchlorate into them. These porous silicon energetic chips could explode strongly at 450-470 ℃ in open air. Ammonium perchlorate is better than sodium perchlorate on the preparation of porous silicon energetic chips.

Abstract:During the process of recrystallizing ultrafine HMX by gas antisolvent (GAS) method,the ultravioletvisible detector was used to measure the supersaturation degree of HMX in CO₂ and acetone system at 10-35 MPa,and the nucleation rate equation was used to calculate the nucleation rate of HMX. The ultrafine HMX was characterized by scanning electronic microscope (SEM). Results show that the supersaturation degree of HMX in CO₂ and acetone system increases with increasing of the pressures. Also,the nucleation rates of HMX are very high,can reach to 10²⁴ orders of magnitude. From results of SEM,there are some obvious differences in particle morphology,size and size distribution of HMX. Analyzing from the view of nucleation rates,there is more energy consumed in nucleation stage at relatively high pressure (35 MPa) than that at low pressure (5-15 MPa),which contributes to formation of HMX particles with regular morphology,small size,narrow size distribution.

Abstract:3,3′-Dicyano-4,4′-azofuroxan was synthesized from malononitrile via nitrosation,oximation,oxidization cyclization and azo-coupling. The yields of the above four steps could be 79.0%,86.8%,61.0% and 71.9% respectively,and its overall yield was up to 30.2% The mechanism of oxidization cyclization was proposed and discussed,and the key factors,including the molar ratio (n) of lead dioxide/1-amino-2-nitrildioxime and reaction time (t),of this process were studied. When n=4/1 and t=4 h,the highest yield of 4-amino-3-nitrilfuroxan could be obtained. The structures of the aim compound and all of the intermediates were confirmed by spectroscopical and elemental analysis.

Abstract:Neopentyl glycol diazo dinitrate(PDADN) was synthesized by one-pot process which consisted of two steps,i.e.nucleophilic substituion of 1,3-dibromo-2,2-dihydroxylmethylpropane(DBDMP) with sodium azide(SA),and nitration of the substituted intermediate (1,3-diazido-2,2-dihydroxylmethylpropane) with nitric acid(NA),but carried out in one pot without separating the intermediate. The factors affecting the yield and purity of PDADN,such as ratio of DBDMP/SA/NA,nitration temperature (T) and time (t) were investigated. The optimized process conditions were: DBDMP/SA/NA (molar ratio)=1.0/2.1/8.0,T=(15~19) ℃,and t=18 min. The yield and purity of the resulting PDADN could be up to 84% and 98% repectively,and the product′s structure was identified with IR,NMR and elemental analysis. To compare with the traditional preparation of PDADN,the one-pot process simplifies the procedures,improves PDADN′s yield and purity,mildens the reaction conditions,and is easy to be industrialized.

Abstract:RDX was synthesized via nitrolysis of 1,3,5-triacylhexahydro-s-triazine with dinitrogen pentoxide（N₂O₅） in organic solvents(acetonitrile,nitromethane,chloroform,thtrachloromethane). The effects of organic media,dosage of N₂O₅,reaction temperature and reaction time on RDX yield have been investigated,which could be up to 63.5% and 75.2% respectively from 1,3,5-triacetylhexahydro-s-triazine and 1,3,5tripropionyllhexahydro-s-triazine with acetonitrile as solvent,and in the following reaction conditions: molar ratio of N₂O₅ to triazine 5:1,temperature 50 ℃,and the 1 h. IR,1H NMR,and elemental analysis confirmed the obtained product structure.

Abstract:Tris-(m-nitrophenyl) bismuthine and tris-p-nitrophenyl) bismuthine were synthesized by Grignard reaction and metal transfer method by using m-chloronitrobenzene,p-chloronitrobenzene and bismuthine chloride as raw materials. The melting point of two unreported energetic bismuth complexs is 76-77 ℃ and 91-92 ℃ respectively. The catalytic effect of curing solid propellant hydroxy-terminated polybutadiene (HTPB) was studied by DTA. The DTA curves for HTPB system added tris-(m-nitrophenyl) bismuthine showed an exothermic peak temperature at 120.2 ℃. The catalytic effect was identified to that as the room-temperature curing catalyst tris-(ethoxyphenyl) bismuthine (TEPB).

Abstract:The fast cookoff of TATBbased PBX explosive with 2 mm thickness steel casing under solid propellant firing in a welldefined scenario such as failed launch of a missile was investigated. In addition,temperature distribution of the TATBbased PBX explosive under solid propellant firing was numerically investigated. Temperature rising was recorded and the heat flux of the explosive surface was calculated with the experimental data and Duhamel superposition principal,the average heat flux on the explosive surface under the solid propellant firing is 19.1 kW·m^-2. Ignition time of TATBbased PBX explosive under the solid propellant firing is 95 s. The experimental results show that fast cookoff of TATBbased PBX explosive under solid propellant firing will not develop into deflagration or detonation.

Abstract:Various microwave effects on explosive materials were summarized in this study including microwave measurement of explosive performance,microwave application to explosives synthesis/preparation/desiccation/recycle,and microwave initiation of explosives materials. From microwave fundamental and selective heating effect to components,it was derivate that hotspot initiation theory should be effective in explanation of microwave initiation process including intentional/accidental initiation experiments and mechanism.

Abstract:Detonation pressure and detonation velocity of RDX-based aluminized explosive with different charge densities and charge sizes were measured by using manganin pressure transducers and probes,respectively. The relationship between detonation pressure and charge density,as well as the relationship between detonation velocity and charge density,were fitted,and then the effects of charge density and charge size on detonation pressure or detonation velocity of RDX-based aluminized explosive were analyzed. The results show that the detonation pressure and detonation velocity are both increasing with the increasing of charge density. When the charge diameter is 20 mm and the charge length is 40 mm,RDX-based aluminized explosive is already at steady detonation,and the charge diameter and the charge length do not affect the measurement of detonation pressure and detonation velocity.

Abstract:The thermal behavior and decomposition mechanism of nitrate glycerol ether cellulose(NGEC) were studied by means of TG/DTG,DSC and solid reaction cell in situ in conjunction with rapidscan Fourier transform infrared spectroscopy (RFSTIR) for measuring the condensed phase decomposition products in real time. The kinetics parameters (activation energy and preexponential factor) and the free energy activation,enthalpy of activation and entropy of activation for decomposition reaction were computed by using the Kissinger′mothod,Ozawa′s method and thermodynamic relations. Based on the characteristic temperature from the nonisothermal DSC curves,the critical temperature of thermal explosion of NGEC was estimated.

Abstract:Effect of contents of plastic nitrocellulose(PNC)on mechanical property and preparation process of casting high energy composite modified doublebase (CMDB) propellant with low smoke were studied by means of HAAKE rheometer and single axes tensile test,and physical crosslinking density(νp) of the CMDB propellants were calculated by means of the B.S.T equation. Results show that the rheology of the CMDB propellants possess characteristics of pseudoplastic liquid,and viscosity (shear rate is 1 s^-1)of the CMDB propellant increases significantly with increase in content of PNC. The leveling property of the CMDB propellant becomes bad with increase in content of PNC; the pot life of the CMDB propellants with various PNC contents are long enough to meet the preparation process of the propellant. It is also found that,appropriate increase in content of PNC is helpful to enhancement of not only the tensile strength at +20 ℃ and +50 ℃ of the propellants，but also physical crosslinking density(νp) of the propellants； and it can also improve continuity and closegrained property of the propellants,and packing effect between binder system and particles.

Abstract:To establish the Γ-Ψ expression of variable burning rate gun propellant with square plate-shape,the factors affecting its gas generation were analyzed theoretically. On the condition of geometric combustion law,the theoretical expression between Γ and Ψ were derived,taking the initial size,burning-rate ratios,and density ratio as the basic parameters. By theoretical calculation,influences of width-thickness ratios,outer-to-total thickness ratios,density ratios and burning-rate ratios on the gas generation rule were discussed. The results show that variable burning rate gun propellant with square plate-shape can control the energy release law by using the appropriate width-thickness ratios,outer-to-total thickness ratios,density ratios and burning-rate ratios. The brisance of gas generation increases by 2.6 times when the inner and outer combustion speed ratio triples.

Abstract:In order to study the factors affecting the conformity of the type and size of the variableburning rate propellant and provide a reference to the actual operation for setting the appropriate parameter,threedimensional flows of variableburning rate propellant solution in the screw were simulated using the polyflow software under different operating conditions. Simulation results show that the volume flow rate of outside layer is directly proportional to the screw velocity. When the screw velocity is different,the high frequency fluctuation values of the volume flow rate are 0. 017%-0. 036%. The fluctuation values of the volume flow rate are directly proportional to the fluctuation values of the screw velocity. The volume flow rate of the outside layer is directly proportional to the entrance pressure. When the entrance pressure is different,the high frequency fluctuation values of the volume flow rate are 0. 024%-0. 025%. When the screw velocity is higher,the fluctuation values of the volume flow rate rapidly increase with the increasing of the fluctuation values of the screw velocity. When the entrance pressure is higher,the fluctuation values of the volume flow rate rapidly increase with the increasing of the fluctuation value of entrance pressure. The fluctuation values of the screw velocity affect the volume flow rate of variableburning rate propellant more largely than the fluctuation values of the entrance pressure.

Abstract:Methods of increasing the oxygen balance of singlebase propellant were studied. The oxygen balance,flame temperature,explosion heat,specific energy and gas component were calculated by the minimum free energy method. The calculated results show that the total amount of combustible gases in the propellant combustion products,contents of H₂,CO and CH₄ decrease with the increasing of ammonium nitrate content. When the content of ammonium nitrate is more than 80%,the combustible gases are completely oxidized to carbon dioxide and water. Experiments were performed on a mixture of one served propellant of some gunlaunched missile with propellant containing ammonium nitrate. Results show that when the content of ammonium nitrate propellant is 50%,the oxygen balance is increased by 39.2%. It reveals that the content of CO in combustion products is decreased by 32.8%,while integral optical density(IOD) is reduced by 36.4% by analyzing the photographs of gun muzzle flame.

Abstract:The properties and the developments of synthesises and applications in propellants and gas generators of energetic materials (ammonium azotetrazolate(AZT),guanidinium azotetrazolate(GZT),triaminoguanidinium azotetrazolate(TAGZT) and so on) were summarized. TAGZT with the advantages of reducing the combusting temperature,enhancing the burning rate of the propellant,producing a lot of gases and exhibiting good detonating performances is supposed to be widely used in the field of explosives,propellants and gas generators. GZT with the advantages of reducing the combusting temperature and producing a lot of gases has been widely used in gas generators.

Abstract:The two routes for synthesis of 3,3-bis(azidomethyl)oxetane (BAMO) were compared. Solvent-free process for the synthesis of BAMO from 3,3-bis(chloromethyl)oxetane (BCMO) by phase transfer catalysis was a good method invented by Malik et al. But Sanderson et al proposed method for the synthesis of BAMO,using tribromoneopentylalcohol (TBNPA) as the raw materials,by the phase transfer catalysis in two steps，that is another good method. Using Wardle et al proposed method for synthesis of PBAMO,the product functionality and the molecular weight are controllable. Boron trifluoride tetrahydrofuran (BF₃?THF) is a very good catalyst to prerare PBAMO from BAMO.

Abstract:2,4-Dinitroanisole (DNAN) is a promising alternative that possesses suitable melt point and adequate properties,may enable the development of a new class of low sensitivity melt-cast formulations for use in IM by virtue of reduced sensitivity. Synthesis and properties of DNAN including thermal characteristic and compatibility with relevant materials were overviewed. As a key ingredient in low sensitivity melt-castable explosives,DNAN-based formulations were also reviewed.

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