Preparation Of CL-20 With Narrow Particle Size Distribution By Micro-mixing Technology

CL-20 is one of the high-energy explosives in the world today.And it has broad application prospects in weapons and equipment.However,the raw CL-20 has sharp edges and corners,a wide particle size distribution,and a large particle size.In order to modify to obtain a multi-scale particle size explosive with narrow particle size distribution,high safety and excellent performance,this paper adopts micro-mixed crystallization technology to prepare narrow particle size distribution CL-20.First,the numerical simulation of the flow field of different types of micromixers was carried out,and then experimental researches were carried out through Y-type micromixer and vortex-type micromixer.The best process conditions for preparing?-CL-20 with narrow particle size distribution were obtained,and the performance tests of the obtained CL-20 samples were carried out.The main work is as follows:(1)The structure of the micromixer has a great influence on the mixing effect of the fluid.Three types of micromixers,such as T-type micromixer,Y-type micromixer and vortex-type micromixer,were selected for the numerical simulation of fluid mixing.At the same time,the baffle-type micromixer was researched on the basis of T-type micromixer and Y-type micromixer.The velocity streamline diagram and volume fraction diagram are generated through numerical calculation,and the mixing effect of the micromixer is analyzed and compared.The results showed that there was obvious stratification in the volume fraction diagrams of the T-type micromixer and the Y-type micromixer.After the baffle was added,the two phases were disturbed,so the two-phase mixing was enhanced.But the baffle is difficult to process,the actual application is limited.The volume fraction diagrams of the vortex-type micromixer showed that the addition of the circular cavity improved the mixing degree of the fluid.(2)The Y-type micromixer was used to explore the process conditions for preparing CL-20 with narrow particle size distribution.Single factor experiments were designed to study the effects of solvent/nonsolvent flow ratio,solvent/non-solvent flow ratio after flow increase,CL-20 concentration and solvent composition on the morphology and particle size distribution of CL-20.The crystal form,thermal performance and impact sensitivity of the samples were characterized and tested.The results showed that when the solvent flow rate was 0.2 m L·min^-1,the non-solvent flow rate was 2 m L·min^-1,the active agent concentration was 2%,a certain proportion of n-heptane and ethyl acetate were added to the collection device,the concentration of CL-20 was 3.6%,and the temperature of the collecting device was at 60oC,the crystal form of recrystallized CL-20 remained?-type.The edges and corners of the products were smaller than that of the raw materials,the coefficient of variance was0.32,the particle size distribution was uniform,and the average particle size was 6.44?m.(3)The vortex-type micromixer was used to explore the the best process conditions for preparing CL-20 with narrow particle size distribution.First,the influence of solvent/non-solvent flow ratio on the crystal form,morphology and particle size distribution of CL-20 was studied.On this basis,two factors of temperature and concentration were selected as the research objects,and L₉(2³)Orthogonal experiment was designed.Two indicators were selected to evaluate the experimental results:crystal form and the coefficient of variance.The analysis results showed that the concentration had a greater influence on the coefficient of variance of the sample than temperature,while the concentration and temperature had the same influence on the crystal form of CL-20.The optimal process conditions were:the solent flow rate was 0.2 m L·min^-1,the non-solvent flow rate was 2m L·min^-1,the active agent concentration was 2%,a certain proportion of n-heptane and ethyl acetate were added to the collection device,the concentration of CL-20 was 7%,and the heating temperature of the collection device was 60oC.Under these conditions,the crystal form of the recrystallized CL-20 remained?-type,the particles were rounder than the raw material,the coefficient of variance was 0.31,the particle size distribution was narrow,and the average particle size was 7.83?m.(4)CL-20 was refined by traditional solvent/non-solvent recrystallization method.Compare it with the samples obtained under the optimum conditions of Y-type and vortex-type micromixers.The particle size statistics showed that the dispersion coefficients of CL-20 prepared by the traditional method,Y-type micro-mixer,and vortex micro-mixer were0.41,0.32,and 0.31,respectively.The smaller the coefficient of variance,the more uniform the particle distribution.From the results of the particle size test,the three groups of samples were all close to the normal distribution.PXRD results showed that?-type CL-20 was prepared by all three processes.DSC test results showed that the apparent activation energy of CL-20 prepared by Y-type and vortex-type micromixers was higher than that of traditional methods.The T_P0 and T_b of the Y-type CL-20 were lower than the vortex CL-20,and the T_P0and T_b of the vortex CL-20 were slightly lower than the CL-20 obtained by the traditional method.Comprehensive comparison showed that the vortex CL-20 had better thermal stability.The mechanical sensitivity test results showed that the characteristic drop heights of CL-20 prepared by the traditional method,Y-type micro-mixer,and vortex-type micro-mixer are 33 cm,37 cm,and 38 cm,respectively.As the coefficient of variance decreased,the impact sensitivity of the three groups of samples gradually decreased,indicating that the samples made by the vortex micromixer have the highest safety performance under impact.