| Microelectromechanical system（MEMS）pyrotechnics put forward new requirements for micro-space and microstructure fine charging technology due to the miniaturization of structure,transducer informatization,sequence integration and functional dexterity.3D micro-jet printing,as a new technology compatible with MEMS process,has unique advantages such as on-demand printing,high precision,and special-shaped micromanufacturing,and has initially realized the micro-space fine assembly and micro-scale detonation transmission capabilities of all-liquid 2,4,6,8,10,12-hexanitro-2,4,6,8,10,12-hexaazaisowurtzitane（CL-20）based booster explosives.However,the CL-20-based booster agent has problems such as poor mechanical properties,easy crystallization,high mechanical sensitivity and single component structure,which limit its application in micro booster sequences.Therefore,on the basis of studying the forming mechanism of energetic ink droplet in 3D micro-jet printing and the forming mechanism of ink droplet condensation,this paper designed and optimized two CL-20 based booster agents,namely full-liquid type and micro-nano particle suspension type,respectively,and preliminarily explored the micro-scale assembly and forming of heterogeneous CL-20 based booster agents by using the dual-nozzle3D micro-jet collaborative printing technology.The main research contents are as follows:（1）Through the research on the forming mechanism of 3D micro-jet printing ink droplet and the agglomeration mechanism of point-to-line system,the evolution mechanism of ink droplet morphology of energetic inks with different physical properties under different micro-jet process parameters was revealed,and the stability phase diagram of 3D micro-jet printing was obtained.The results showed that the pulse width had a linear positive correlation with the volume of the ink droplet and a linear negative correlation with the flight speed,and the correlation decreased with the increase of the ink viscosity.The pulse stroke and intake pressure had linear positive correlation to the volume and flight velocity of the ink droplet.According to the mechanism of droplet morphology evolution with different physical characteristics,the 3D microjet stability phase diagram was obtained,which was defined by dimensionless parameter Z and viscosityη（2.17<η<22.36 m Pa·s,2<Z<22）.By adjusting the pulse cycle and the printing speed,the ductility of the ink droplet in the printing direction could be controlled.The distribution lines of the ink droplet were developed from discrete single point to fan-shaped line,uniform line,convex line and stacked line,and the accuracy of the distribution lines reached 198～206μm.When the substrate temperature reached 55℃,the"coffee ring"phenomenon of the drug line could be effectively inhibited.（2）In order to obtain a CL-20-based micro-nano structure booster explosives with enhanced mechanical properties,CL-20-based energetic ink with both high density and high strength was designed according to the stability phase diagram of 3D microjet printing,with the dual network physical cross-linking of rigid macromolecules and flexible small molecules and GO 2D plane structure enhancement technology.The results showed that when the mass ratio of rigid nitrocellucotton（NC）to flexible polyazide glyceryl ether（GAP）in the full-liquid CL-20 energetic ink was 3:7,the internal microstructure of the sample was dense,the porosity was reduced to 14.54%,the elastic modulus was up to 6.46 GPa,and the CL-20crystal in the micro-jet samples was transformed intoβtype.Through the design of small-molecule polyethylene glycol（PEG）bonding system and the combination of functional agent GO,the internal microstructure of CL-20/NC/PEG/GO samples was uniform and compact,the elastic modulus was increased to 9.01 GPa,and the measured detonation velocity was more than 93%of the theoretical detonation velocity,showing excellent detonation performance.The strengthening mechanism of small molecule PEG and the functional aids GO and CL-20 was mainly due to the sufficient dual network physical entanglement of rigid macromolecules and flexible small molecules and the self-assembly between oxygen-containing functional groups and complexes in GO 2-D confined domain environment.（3）In order to solve the crystallization problem of CL-20-based energetic ink in the process of 3D micro-jet printing,micro-nano CL-20 particles were used as the main explosive,polyvinyl alcohol（PVA）as the binder,water and ethanol as the composite solvent,the micro-nano CL-20 particle suspension energetic ink was designed with the help of the electrostatic repulsion and steric hindrance effect of the binder and the double solvent.By studying the group effect relationship of PVA concentration,micro-nano CL-20 particle content and double solvent system on suspension stability,the stable time of energetic ink could reach more than 36 h.The microstructure of CL-20/PVA samples formed by 3D microjet printing had compact structure,the porosity of 13.81%andε-type crystal.Compared with the full-liquid CL-20-based energetic ink,the impact sensitivity and friction sensitivity were decreased by 166%and 87.5%,respectively,and the apparent activation energy was increased 40.63 k J·mol-1,which effectively improved the safety performance of micro-nano structure booster explosives.The PVA@polyaniline（PANI）bonding system was constructed by the covalent cross-linking method of dynamic borate bond,and micro-nano particles suspended CL-20/PVA@PANI energetic ink was prepared.The microstructure of the 3D micro-jet printed CL-20/PVA@PANI samples was uniform and dense,and the adhesion level was improved by 4 levels.The detonation speed was up to 7884 m·s-1,and the static inductance reached 0.194J,It had good toughness,viscoelasticity and safety performance,and had a good application prospect in the micro-detonation sequence.（4）In order to obtain CL-20-based micro-nano structure booster explosives with adjustable comprehensive performance,combined with the high strength characteristics of full-liquid Cl-20-based energetic ink and the high adhesion characteristics of micro-nano particulate suspension energetic ink,the dual-nozzle 3D micro-jet co-printing technology was used to assemble and design the ordered heterogeneous structure of CL-20-based micro-nano structure booster explosives.The maximum density of the sample formed by collaborative printing was 91.8%of the theoretical density,the interlayer connection of alternating printing was dense,the activation energy was increased to 190.7 k J·mol-1,the detonation speed was up to 8122 m·s-1,and the stable detonation could be achieved in the micro-scale groove.The gradient deposition of heterogeneous structures of CL-20 based energetic composites were realized through the collaborative printing design of 3D micro-jet with double nozzle,so that it had the characteristics of high energy,passivity and high adhesion.The ordered assembly of micro-energetic composites was realized to a certain extent,which provides a new way for the functional regulation and application of energetic composites micro-charge. |
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