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Abstract:

Abstract:In order to achieve the safety of the preparation process of ultrafine zirconium （Zr） powder， a method for preparing core-shell Zr powder by continuous flow at microscale was studied. A continuous microfluidic system consisting of microfluidic unit and spray-drying unit was established to verify the feasibility. The system can realize the microscale mixing of components， the formation of core-shell structure and the post-processing of samples continuously. Using Zr powder and nitrocellulose （NC） as composite components， the structure regulation of Zr@NC was studied by controlling content of NC and adjusting dry gas pressure at the microscale. In addition， the activity and safety of Zr@NC were analyzed by thermal analysis and electrostatic spark sensitivity test. The results show that the Zr powder with uniform morphology and core-shell structure can be prepared by the continuous microfluidic system. Thermal analysis results show that the oxidation weight gain of Zr@NC is only 1.04% lower than that of the raw Zr， and the energy release is faster. According to the electrostatic spark sensitivity test， it was found that the 50% ignition energy of Zr@NC is increased from 1.42 mJ to 197.82 mJ compared with the raw Zr， which means the electrostatic spark sensitivity is greatly reduced.

Abstract:In order to improve the economic benefit of producing 2，2，4-trimethyl-1，3-pentanediol（TMDP）， a more efficient and safe microchannel continuous flow process was selected to replace the traditional kettle-type batch production method with using isobutyl aldehyde as raw material and sodium hydroxide solution as catalyst. The effects of catalyst sodium hydroxide concentration， dosage， temperature and residence time on the reaction were investigated. The optimum conditions were determined as follows： sodium hydroxide concentration 50%， v（isobutyral）∶v（NaOH）=1， residence time 10 min， reaction temperature 40 ℃. Under these conditions， the conversion of isobutyraldehyde was 99.02%， the selectivity of TMDP was 93.57%， and the yield was 92.65%. The process made full use of the excellent mass and heat transfer characteristics of the microchannel reactor， greatly shortened the reaction time， increased the reaction rate， extended the selection range of process conditions， and realized the effective control of the reaction process of hydroxylaldehyde condensation. At the same time， the kinetic studies were carried out at different temperatures and concentrations of sodium hydroxide， and the kinetic equations and corresponding parameters were obtained with the concentration of sodium hydroxide being 50% and 45% respectively. The macroscopic kinetics obtained by fitting is second-order， and the activation energy and pre-exponential factors are： 26.34 kJ·mol^-1， 2888.26 L·K^-1·mol^-1·min^-1.

Abstract:A measurement method of explosive crystallization thermodynamic parameters based on optofluidics was proposed to obtain the crystallization thermodynamic parameters such as solubility and metastable zone width of explosive crystal， and the applicability of this method was verified by taking HNS explosive as a sample. The solubility of HNS in DMSO/DMF solvent system with volume ratio of 10∶0， 7∶3， 5∶5， 3∶7 and 0∶10 from 318.15 to 353.15 K and the metastable zone width of HNS in the above DMSO/DMF solvent system from 318.15 to 333.15 K were measured with a step of 5 K. Apelblat model and λh model were employed to fit the collected solubility data. The effect of solvent system on the metastable zone width was studied， and the crystallization parameters were screened. According to the classical nucleation theory， the apparent nucleation order m of HNS was calculated， and the nucleation mechanism of HNS by cooling crystallization was analyzed. The results indicate that the measurement method of crystallization thermodynamic parameters based on optofluidics exhibit exceptional applicability to HNS crystals. With the increase of temperature and the volume ratio of DMSO in the system， the solubility of HNS increases. With the increase of DMSO volume ratio in the system， the width of metastable zone becomes narrower. The optimum crystallization conditions are as follows： pure DMSO is utilized as solvent， the solution temperature is set at 333.15 K， and the solute concentration is 0.029 g·mL^-1. The value of m is approximately 4， which is not affected by the initial temperature. It can be inferred that the nucleation mechanism of HNS belongs to continuous nucleation.

Abstract:To control the morphology， particle size distribution and coating covering effect of high polymer binder explosives （PBXs）， TATB/F2602 microspheres could be prepared via high sensitivity droplet microfluidic technology， and investigated the effects of binder content and flow rate on the morphology and particle size of TATB-based microspheres. Moreover， it studied the morphology， structure， composition and thermal behavior of microsphere samples systematically using scanning electron microscopy， X-ray diffraction， specific surface area， DSC and TG， respectively. Results show that， when the binder content is 5%， the microspheres have smooth surfaces， regular spherical shapes and high spherical monodispersity， and the average roundness is 0.921 （span=0.04）. With the increase of flow ratio， the D₅₀ of microsphere sample decreased from 51.73 to 44.31 μm， and the particle size distribution is narrow （span<0.4）. Fluororubber （F2602） is uniformly distributed in the interior and surface of TATB microspheres， and uniform coating of TATB particles delay the thermal decomposition of microspheres by 4.08 ℃. Compared with raw TATB， the true density of TATB/F2602 increases to 1.9780 g∙cm^-3 during spheroidization. The droplet microfluidic technology can effectively control the morphology and particle size of explosive microspheres， and provide experimental reference for the spherical preparation of polymer bonded explosives.

Abstract:Nano 2，6-diamino-3，5-dinitropyrazine-1-oxide （LLM-105） was prepared by ultrasound-assisted microfluidic technology based on the solvent and non-solvent method to improve the morphology and reduce the particle size. The microscopic morphology and crystal structures of the samples were characterized by field emission scanning electron microscopy （FE-SEM） and X-ray diffraction （XRD）. In addition， The promotion of fluid mixing by ultrasonic method was demonstrated by fluid visualization. The results showed that the spherical particles prepared by ultrasound were smaller and homogeneous， with an average particle size of 137.65 nm. Meanwhile， the crystal structures remained unchanged from the raw material. Differential scanning calorimetry （DSC） showed that the thermal decomposition temperature of nano-LLM-105 was reduced compared to the raw material， demonstrating that ultrasonic assistance can not only improve the efficiency of preparing nano-LLM-105， but also significantly reduce the particle size.

Abstract:The conventional lead azide （Pb（N₃）₂， LA） preparation process has problems such as the risk of self-explosion. Aiming at the above problems， the spin-T microfluidic chip with the characteristics of short diffusion distance， large specific surface area， and continuous reaction was used as a microreactor. And then， the LA primary explosive synthesized by microfluidics was spherically modified by using the flow-focusing droplet chip. The effects of the flow rate， crystal form control agent， and other factors on the product were investigated by SEM， XRD， and DSC. The sensitivity and explosion performance of microfluidic LA， microsphere LA， and powder LA were compared. The results show that by controlling the microfluidic reaction parameters， the particle size of the LA can be effectively controlled， and they were all α-type. After the spheroidization， the impact sensitivity H₅₀ （25.5 cm to 12.1 cm） was significantly improved， but the electrostatic spark E₅₀ （1.98 kV to 2.97 kV） and flame sensitivity L₅₀ （26.3 cm to 16.1 cm） were reduced. At the same time， the detonation pressure was increased （by 63.6%）. It shows that the microfluidic technology was an effective method that can safely prepare and modify the LA primary explosive， which provided an idea for the controllable preparation and regulation of sensitive primers.

Abstract:In order to explore a continuous， safe and controllable microfluidic synthesis strategy of emulsion explosive， silicon-based microporous array chips with four apertures（10 μm，20 μm，30 μm，40 μm） were designed and prepared by MEMS technology， and the microfluidic reaction device of emulsion explosive was constructed. It is found that the main factors affecting the droplet size of dispersed phase in latex matrix are micropore diameter and continuous phase velocity. The effects of pore size and oil-water two-phase flow rate on the particle size distribution and exothermic properties of emulsion droplets were studied. The results show that the particle size distribution of dispersed droplets in the matrix is the narrowest when the pore size is 30 μm and the continuous phase flow rate is 0.5 mL·min^-1 and D₅₀=8.169 μm. Microporous array chip can generate highly homogeneous droplets in batch， which provides a new choice for emulsification in the preparation of emulsion explosive.

Abstract:1²，1⁴，1⁶，3⁴，3⁶，5²，5⁴，5⁶，7⁴，7⁶-decanitro-2，4，6，8-tetraoxa-1，3，5，7（1，3）-tetrabenzenacyclooctaphane-1⁵，5⁵-diol （ZXC-51） was obtained from phloroglucinol and 1，3-difluorobenzene through nitration and cyclization. A series of calixarene energetic salts were received by the reaction between ZXC-51 and different organic base. The single crystal structures of compound ZXC-51 and its four salts were proved by X-ray single crystal diffraction analysis. And the structures of these compounds were also characterized by NMR and elemental analysis. Meanwhile their thermal properties were also analyzed by differential scanning calorimetry. The detonation and safety performance of ZXC-51 were studied. The results show that its theoretical detonation velocity and detonation pressure are 8193 m·s^-1 and 31.18 GPa respectively. And its impact sensitivity is 36 J and the friction sensitivity is more than 360 N.

Abstract:To improve the yield and purity of 2，6-dimethyl-4-hydroxyphenylpentazole， the preparation method of 2，6-dimethyl-4-hydroxyphenylpentazole （DMAPH） crystal， the raw material of arylpentazole， was investigated through three steps including nitrification， reduction and salification from 2，6-dimethylphenol （DMP）. The structure， crystal morphology and stability were characterized with infrared spectroscopy （IR）， single crystal X-ray diffraction （SCXRD）， scanning electron microscopy （SEM）， powder X-ray diffraction （PXRD）， differential scanning calorimetry （DSC） and theoretical calculation. The results reveal that the yield of 2，6-dimethyl-4-nitrosophenol is up to 90% in the presence of glacial acetic acid and sodium nitrite. The different shapes of DMAPH crystal including sheet， needle， block and plate morphology can be obtained by changing the solvent， while the temperature only affect the particle size of precipitated crystals. The （400） face is the main crystal face of DMAPH crystal from methanol， while in other solvents it is the （214） face. The DMAPH crystals exhibit good thermal stability with decomposition peak temperature ranging from 220-240 ℃. In contrast to amorphous DMAPH powders， the crystalline DMAPH solids have better stability in air， and are more suitable for long-term storage.

Abstract:Hexanitrohexaazaisowurtzitane （CL-20） and nano-aluminum powder are commonly used for the improvement of energy density in explosive formulations， however， the high mechanical sensitivity of CL-20 or their mixture has been impeded further applications. Therefore， it is very meaningful to obtain a low-sensitivity of CL-20 and Al uniform mixture. In this paper， the Pickering emulsion was prepared by using nano-aluminum powder modified by perfluorocarboxylic acid as the surfactant （F-Al）， and the ethyl acetate solution of CL-20 and TNT as the oil phase. The influence law of F-Al powder content and static duration on the stability of the emulsion was investigated. The spheroidicity core-shell CL-20/TNT co-crystal@Al composite was successfully prepared. Its morphology， crystal form， thermal decomposition properties， safety， etc. were characterized. Results show that stable emulsions can be obtained when the content of F-Al powder is 1%， 10%， and 20% and static duration is less than 100 min. XRD results showed that the CL-20 and TNT cocrystals was obtained. The crystal size （20-40 μm）， the ellipsoid-like morphology， the uniformly coated nanosized F-Al powder were shown by the SEM images. An H₅₀ value of 35 cm and a friction sensitivity explosion probability of 30% have been realized for that of composites， which is much higher than that of CL-20. The preparation method used in the present paper does not sacrifice the energy density in the spheroidicity core-shell CL-20/TNT co-crystal/Al composite， which is expected to provide a pathway to the design and prepare of high-energy propellants and explosives containing CL-20 and Al.

Abstract:ReaxFF molecular dynamics （ReaxFF MD） simulations were adopted to identify the main intermediate products， final products and chemical reactions during 3，4-dinitro-1H-pyrazole （DNP） thermal decomposition. Accelerating rate calorimeter （ARC）-mass spectrometer （MS） technique was adopted to study DNP thermal decomposition properties and identify the gaseous products. The simulated results illustrate that C₃HO₄N₄， C₃HO₃N₄， C₃HO₂N₃， C₃HNO₂， NO₂ are the main intermediate products， and H₂O， CO₂， N₂ are the main final products. MS detected main gaseous products are H₂O， CO₂， N₂ as well. According to the simulation results， the produced time and abundance of the products are obtained as well. Among which C₃HO₃N₄ is the first generated intermediate product， and H₂O is the first generated final product. C₃HO₃N₄ and N₂ are the intermediate and final products with the largest amount， respectively. Additionally， the main chemical reactions in DNP thermal decomposition process are also acquired by molecular dynamics simulations. According to the generation time and abundance of products， the decomposition path of DNP was obtained.

Abstract:To investigate the influence of the loading density of main propellant charge on the propagation characteristics of ignition charge gas in the granular propellant bed， the test platform for ignition and propagation of a large-diameter dense propellant bed was established， and the flame sequence diagram and the pressure changes of partial pressure gauges were recorded in tests. The porous medium model was used to simulate the granular propellant bed in the charge chamber， and the ignition and propagation model corresponding to the test device was established to numerically simulate the flow process of ignition charge gas in the granular propellant bed. The simulation results were compared with the test results to verify the reliability of the model， and then the propagation characteristics of temperature and pressure fields of gas in the propellant bed with different loading densities were calculated. The results show that the calculated results are in good agreement with the experimental flame propagation sequence process and the experimental pressure histories， which verifies the reliability of the model. Under the condition of any porosity， the axial displacement of flame front develops rapidly and the axial velocity decreases from 25-30 m·s^-1 to 10 m·s^-1 during 0-10 ms， ， and the axial velocity decreases to 2-3 m·s^-1 during 10-40 ms. Similarly， under the condition of any porosity， the development of radial displacement of flame front is concentrated during 2.2-3 ms， and the radial velocity decreases to 20-22 m·s^-1 at 3 ms. However， the radial velocity at the initial time is large for large porosity. When the porosity increases from 0.3 to 0.5， the pressure difference at different positions in the chamber decreases 16.7% from 0.24 MPa to 0.20 MPa， and the uniformity and instantaneity of ignition are improved. With the increase of porosity， the axial and radial resistances of the flame front in propagation process decrease， the axial expansion displacement of the flame front and the initial velocity of flame propagation in the axial and radial directions increase， but the final velocity tends to be the same. The smaller the pressure in the chamber， the smaller the pressure difference in the chamber.

Abstract:The comprehensive performance of explosives depends not only on their chemical components， but also on their structures and morphologies to a greater extent. Microfluidics has become a new research focus owing to its superb mass transfer and heat transfer efficiency， precise parameter control and intrinsic safety. This paper analyzed and summarized the research status of droplet flow and continuous flow in the aspects of particle size， particle size distribution， crystal morphology and aggregate structure of primary and high explosives. The stable reaction environment and flexible residence time of the droplet flow are applicable to the structural control of the primary explosives， and the superior size uniformity and monodispersity of the droplet flow are appropriate for the preparation of spherical explosive particles. The high mixing efficiency of the continuous flow is in line with the crystalline properties of the high explosive. Combined with the deficiencies of current related research in post-processing methods， theoretical applicability， microfluidic manipulation methods and the degree of intelligence， suggestions and ideas for the further development of microfluidic technology in the field of explosives were put forward.