Preparation And Characterization Of High Energy Insensitive CL-20-based Composite Microspheres

Hexanitrohexaazaisopentane（HNIW,also known as CL-20）,as a“breakthrough fourth-generation energetic material”,is widely used in weapons and equipment because of its high detonation speed and high energy density.However,its mechanical sensitivity,shock wave sensitivity and electrostatic spark sensitivity make its safety performance contrary to the requirements of modern battlefield environments.Spherical materials exhibit excellent comprehensive performance due to their compaction effect,high surface energy and high surface activity.Therefore,the preparation of low-sensitivity spherical CL-20-based composite energetic materials is of great significance for improving its performance,making it better adaptable,and broadening the scope of application.The detailed contents of this research are as follows:（1）Based on molecular dynamics,the performance of FOX-7/CL-20 and LLM-105/CL-20 composite systems with different mass ratios was simulated separately to study the molecular interaction between components.Parameters such as bond length,binding energy,cohesive energy density and mechanical properties of each system were calculated.The results showed that the maximum bond length(L_max)and average bond length(L_ave)of N-NO₂ in the two types of composite systems gradually became shorter with the increase of the content of the insensitive components FOX-7 and LLM-105,and the cohesive energy density gradually increased,indicating that the introduction of the insensitive components such as FOX-7 and LLM-105 makes the sensitivity of the system decrease.When the mass ratio of FOX-7 and CL-20 was 2:8,the binding energy of the FOX-7/CL-20 system was maximum,the interaction was the strongest,and the mechanical properties were better.The binding energy of the LLM-105/CL-20 composite system with LLM-105 mass percentage of30%is maximum.（2）Spherical CL-20,FOX-7,LLM-105 energetic materials were prepared using spray drying technology.First,the CL-20 microspheres were prepared and the effects of solvent type,precursor solution concentration,inlet temperature,nitrogen rate,and other parameters on the product were analyzed.And the optimum conditions for the preparation CL-20microspheres are as follows:the proportion of m（acetone）:m（ethyl acetate）for 1:1,the inlet temperature of 80℃,solution concentration of 50 mg/mL,the feed rate of 20 mL/min,and nitrogen rate of 30 L/min.CL-20 microspheres had a smooth surface with a median particle size of about 1μm.Compared with the raw CL-20,the characteristic drop height value increased from 13.4 cm to 34 cm,the explosion probability value decreased from 100%to80%,and the desensitization effect was obvious.Then,the FOX-7 microspheres and LLM-105 microspheres were successfully prepared by spray drying,and the morphology,thermal performance and mechanical sensitivity were characterized,respectively.The spray drying process does not change the crystal structure of the two explosives.The FOX-7microspheres have high thermal stability,their characteristic drop height is 130 cm,and the explosion probability is zero.The characteristic drop height of LLM-105 microspheres exceeds 150 cm,and the explosion probability is zero.（3）Based on the conclusion of molecular dynamics simulation,FOX-7/CL-20 composite microspheres with 15%,20%,25%and 30%mass fractions of FOX-7 were prepared by spray drying method,respectively.The optimum conditions for the preparation of FOX-7/CL-20composite microspheres are as follows:inlet temperature at 70℃,a feed rate of 20 mL/min,the nitrogen flow rate of 70 mL/min,the feed liquid concentration of 5 mg/mL,and the formation mechanism was analyzed.Scanning electron microscope（SEM）,powder X-ray diffractometer（PXRD）,and differential scanning calorimeter（DSC）were used to investigate the morphology,crystal structure and thermal properties of FOX-7/CL-20 composite microspheres with different mass ratios.The mechanical sensitivity also was tested.The results show that the FOX-7/CL-20 composite microspheres with different mass ratios have better formability and are all spherical-like structures.The greater the CL-20 content,the more conducive to the spheroidization of the composite particles.The diffraction intensity of the prepared FOX-7/CL-20 composite microspheres was significantly reduced,showing the characteristics of typical micro-nano particles.The diffraction peak width did not change significantly,and the prepared composite particles had good crystallinity.The thermal stability of FOX-7/CL-20 with different mass ratios is better than that of a single CL-20microsphere prepared by spray drying,and the thermal performance is relatively good when the FOX-7 content is 25%.Compared with the raw CL-20,the characteristic drop height values of the four mass ratio FOX-7/CL-20 composite microspheres was increased to 44.87cm,53.36 cm,60.62 cm and 64.25 cm,respectively;the explosion probability of friction sensitivity was reduced to 10%,40%,55%and 72%,which implied the mechanical sensitivity is significantly reduced.（4）Based on molecular dynamics simulation,LLM-105/CL-20 composite particles with LLM-105 mass ratio of 30%were prepared by three methods:suspension spray drying,co-solution spray drying and mechanical ball milling.The thermal decomposition performance and mechanical sensitivity were characterized,and the detonation performance was predicted.The following conclusions were obtained.LLM-105/CL-20 composite microspheres in particle size of about 3μm with regular morphology were assembled by numerous nanoparticles.The LLM-105/CL-20 composite explosive prepared by the co-solution spray-drying method has a particle size of about 2μm and microspheres with a smooth surface,but some particles have holes on the surface.The particle size of LLM-105/CL-20 composite explosive prepared by ball milling is about 1μm,which is a typical physical mixture.The XRD patterns of the LLM-105/CL-20 composite particles prepared by suspension spray drying and mechanical ball milling are superimposed on the characteristic peaks of the raw materials CL-20 and LLM-105.The two preparation processes did not change the two components of crystal structure.But,the crystal form of the composite microspheres prepared by the co-solution spray drying method was changed.Compared with the spray-drying single component CL-20,the thermal stability of the composite particles prepared by the three methods was improved,and the thermal stability of the composite microspheres prepared by the suspension spray drying method was the best.Compared with CL-20 raw materials,the characteristic drop height values of LLM-105/CL-20 composite energetic materials prepared by suspension spray drying method,co-solution spray drying method and mechanical ball milling method are 87.91 cm,79.24 cm and 57.22 cm,respectively,the friction sensitivity was reduced to 22%,26%and 45%,respectively.The mechanical sensitivity of the LLM-105/CL-20 prepared by the three methods was significantly reduced.The theoretical density of LLM-105/CL-20 composite explosive is1.999 g/cm³,and the detonation velocity reaches 9440.25m/s.