Construction Of Nano-Explosives@CL-20 Core-Shell Complexes Based On Pickering Emulsion

Improving the energy and safety performance of weapons is the development goal of modern military equipment,and the main way is to prepare high-energy and low-sensitivity explosives.However,there has been a contradiction between high energy and low susceptibility,and it is difficult to reduce the susceptibility of explosives while ensuring high energy.As the most popular high-energy single-mass explosive,the high sensitivity of hexanitrohexaazapentane（CL-20）severely limits its application in military fields.The small particle size,large specific surface area and low mechanical susceptibility of nano energetic materials,however,are unstable and highly prone to agglomeration,making them difficult to be applied in practice alone.In this paper,CL-20 and nano-explosives are combined to prepare a spherical core-shell complex by the Pickering emulsion method to improve the thermal stability and safety performance of CL-20.The main findings are as follows:（1）The refinement experiments were performed on the insensitive explosives3,3’-diamino-4,4’-azafurazan oxide（DAAF）and 2,6-diamino-3,5-dinitropyrazine-1-oxide（LLM-105）.The nano-DAAF and nano-LLM-105 were prepared by homogeneous spraying of explosive solution into low temperature non-solvent using solvent non-solvent method and reverse dosing method.Through the single factor control method,the optimum process conditions for the refinement of the two explosives were found respectively.The process conditions for the preparation of DAAF nanoparticles were as follows:N,N-dimethylformamide（DMF）as the solvent,water as thr non-solvent,polyvinylpyrrolidone（PVP）as the surfactant,stirring speed of 500 rpm,and solvent-non-solvent volume ratio of 1:30.The process conditions for the preparation of well-dispersed LLM-105 with the particle size of 100-400 nm were as follows:dimethyl sulfoxide（DMSO）as the solvent,water as the non-solvent,PVP as the surfactant,stirring speed of 800 rpm,and solvent-non-solvent volume ratio of 1:30.The XRD and DSC results showed that the crystalline shape of DAAF and LLM-105 after recrystallization was unchanged and the thermal stability was reduced.（2）The prepared nano-explosives were modified with stearic acid to change their surface hydrophilic and lipophilic properties,and spherical core-shell complexes of CL-20@DAAF and CL-20@LLM-105 in the particle size range of 50-100μm were successfully prepared by Pickering emulsion method and characterized in series.The results showed that the nano-DAAF and LLM-105 particles successfully attached to the surface of CL-20 and formed the shell layer of the spherical core-shell complex.Compared with the raw material CL-20,the exothermic peaks of the complexes were delayed by 9.3°C and 9.4°C,the characteristic drop heights(H₅₀)were increased by 24 cm and 21 cm,and the explosion probabilities（P）were reduced by 58%and 62%,respectively,which proved that the spherical core-shell structure effectively improved the safety performance of CL-20.（3）CL-20/TNT eutectic@DAAF and CL-20/TNT eutectic@LLM-105 spherical core-shell complexes were successfully prepared by the Pickering emulsion method by adding2,4,6-trinitrotoluene（TNT）to CL-20 solution with a molar ratio of 1:1 between the two and using modified nano-explosives as surfactants.The process conditions for the preparation of stable emulsions of CL-20,TNT and DAAF by mechanical stirring were found to be 10 wt%of DAAF,1:5 oil to water volume ratio,0.0660 g of CL-20 and 0.0340 g of TNT,and the resting time was within 20 min.And the particle size of the CL-20/TNT co-crystal@DAAF spherical core-shell complex obtained after extraction and drying was about 80μm,and the H₅₀and P values were 45 cm and 28%,respectively.The process conditions for the preparation of CL-20,TNT and LLM-105 emulsions by mechanical stirring were as follows:LLM-105 content of 10 wt%,oil-water volume ratio of 1:7,CL-20 content of 0.0660 g,TNT content of 0.0340 g,and a resting time of less than 20 min.The particle size of the obtained CL-20/TNT co-crystal@LLM-105 spherical core-shell complex was about 60-90μm,and their H₅₀and P values were 38 cm and 34%,respectively.The results show that this method,which combines various sensing reduction techniques such as eutectic,spheroidization and cladding,could significantly improve the safety performance of CL-20 and is expected to advance the practical application of CL-20-based explosives and nano energetic materials.