Numerical Simulation Of Flow Field In Jet Crystallizer And Preparation Technology Investigation Of Ultrafine FOX-7

1,1-Diamino-2,2-dinitroethylene?FOX-7?is a novel type of high-energy insensitive single-compound explosive,which has good application prospects in insensitive munition.However,the poor quality of the currently synthesized FOX-7 particles is mainly reflected in the irregular particle morphology,large particle size and wide particle size distribution,which limits its application in new composite explosives.This paper focuses on the jet crystallization technology of energetic materials and the jet crystallization process of FOX-7was experimentally studied through the self-designed jet crystallization equipment,based on the numerical simulation of the turbulent field in the jet crystallizer.Furthermore,the morphology,particle size distribution and crystal structure of the FOX-7 products were characterized and the thermal stability and mechanical sensitivity were tested.The main contents are as follows:?1?The structure of the mixing cavity of the jet crystallizer has a great influence on the turbulent mixing of the internal flow field.Four structural parameters related to the entrance and exit of the mixing cavity were selected as the research objects and L₁₆?4⁴?orthogonal experiment was designed.Software Gambit 2.4.6 was adopted to establish sixteen geometric symmetry models of jet crystallizer before meshing them,in which the mesh interval was set to ensure sufficient mesh quantity and accuracy.The quality of the grid was evaluated by the two indexes of EquiAngle Skew and EquiSize Skew.The results showed that the divided grid had sufficient accuracy,which ensured the reliability of the calculation results.?2?Software Fluent 16.0 was used to numerically simulate the flow field in the jet crystallizer,and three indicators were selected to evaluate the simulation results:fluid velocity,turbulence intensity and anti-solvent volume fraction and the values at the preset reference position were extracted for quantitative analysis.The results of the orthogonal experiment showed that the structural parameter which had the greatest influence on the fluid turbulence in the crystallizer was the inlet“a”of the mixing cavity.Through comprehensive consideration of the simulation results of the three indicators,the optimal structure parameters which contributed most to the fluid mixing effect in the jet crystallizer were:a=1.5 mm,b=3.2 mm,c=8.9 mm,d=4.0 mm.It can be drawn from the simulation verification experiment of the optimal model that it was superior to the original model in three indicators.?3?Self-designed jet crystallization equipment was used to investigated the effect of experiment conditions on the morphology and particle size distribution of FOX-7 products.Single factor experiments were designed and the effects of solvent/anti-solvent ratios,solution concentrations,solvent/anti-solvent temperatures and solvent types on FOX-7 crystals were studied.The morphology and particle size distribution of FOX-7 products were characterized by scanning electron microscope,image particle analysis system and laser particle size distribution analyzer.The results showed that spherical FOX-7 particles with smooth surface and regular shape were prepared under conditions of:room temperature of 20?,dimethyl sulfoxide?DMSO?as the solvent and pure water as the anti-solvent,FOX-7/DMSO solution concentration of 0.3 g·ml^-1 and solvent/anti-solvent ratio of 1:12.Particle size test results showed that the particle average aspect ratio was 1.2 and the sphericity reached 0.93 with a narrow particle size distribution ranging from submicron to micron level?D10=0.703?m,D50=1.405?m,D90=3.446?m?.In addition,PXRD results showed that the crystal form of the FOX-7 particles prepared by jet crystallization technology was stable,consistent with the raw material,and was still?-type.For comparison,micron-sized FOX-7 particles with an irregular morphology were prepared by dropwise addition method,and the particle average aspect ratio was 1.4,the sphericity was 0.76,and the particle size distribution was D10=0.662?m,D50=3.316?m,and D90=7.028?m.?4?The thermal decomposition performance of raw FOX-7 and products was tested by a differential scanning calorimeter?DCS?at different heating rates.The results showed that the activation energy of the FOX-7 product prepared by dropwise addition method was 2.66kJ·mol^-1 higher than that of the raw FOX-7,and the₄0) and_{?7? were relatively close to the raw material,while the apparent activation energy of spherical FOX-7 was increased by 14.62kJ·mol^-1 compared to raw FOX-7,and its40} and₍?7? increased by 7.7 K and 7.41 K respectively,indicating that the thermal stability has been improved.On the other hand,the mechanical sensitivity test results showed that,compared with the raw material,the FOX-7product prepared by dropwise addition method had a characteristic drop height of?97.5±1.9?cm and the probability of explosion under friction was?16±4?%,while the impact sensitivity of spherical FOX-7 was reduced by 44.3%and the friction sensitivity was reduced by 80%,which showed that the safety performance of spherical FOX-7 under mechanical action was obviously improved.