Construction Of CL-20 Based Superfine Composite Energetic Materials By Spray Drying And Study On Their Properties

Hexanitrohexaazaisopentazine（CL-20）has the advantages of high detonation velocity,high detonation pressure,and high detonation heat,it is currently the highest energy elementary explosive that can be practically used.However,the higher sensitivity and poor safety of CL-20 restricted its application.So,this work was devoted to solving the problems of CL-20 with irregular morphology,wide particle size distribution,and poor safety.Firstly,the spray drying method was used to prepare superfine spherical CL-20,and the orthogonal experiment was adopted to explore the optimal process parameters.Secondly,based on the optimal process parameter of superfine spherical CL-20 process parameters,the Estane 5703,F₂₆₀₂,and PVAC were added with CL-20 as the binder.Finally,the spray drying method was used to prepare CL-20/（HMX,RDX,AP）co-crystal materials,the effect of surface coating modification and co-crystal types on the sensitivity of CL-20 was studied.The details were as follows:（1）Firstly,superfine spherical CL-20 was prepared by spray drying technology.Ethyl acetate was used as the solvent for spray drying.In order to study the effects of concentration,inlet temperature of spray drying and feeding speed on the morphology and structure of superfine spherical CL-20,an orthogonal experiment with three factors and four levels was designed.The particle size(D₅₀)and morphology of CL-20 prepared by spray drying were selected to evaluate the superfine spherical CL-20.The results showed that the optimum parameters for the preparation of superfine spherical CL-20 by spray drying are as follows:the concentration of CL-20 was 80 mg/m L,the inlet temperature was 80℃,and the feeding speed was 10%（about 3.33 m L/min）.The performance test and analysis of the superfine spherical CL-20 prepared under this parameter showed that the morphology of the prepared ultrafine spherical CL-20 was dense spherical,the D₅₀was 4.968μm,and the crystal type changed toβtype.The activation energy and T_p0of superfine spherical CL-20 were increased by 14.18 k J/mol and 16℃,respectively,the critical temperature of thermal explosion（T_b）increased by 15.81℃,and the minimum initiation energy increased by 10%.（2）Secondly,based on the process parameters of preparing ultrafine spherical CL-20,three different binders(Estane 5703,F₂₆₀₂and PVAC)were selected as coating materials to modify CL-20.The tested results showed that the CL-20 crystal form of the prepared CL-20/binder(Estane 5703,F₂₆₀₂,PVAC)composite energetic material（hereinafter referred to as CL-20/binder composites）was pureβtype.When the inlet temperature and the binder content were 70℃and 2%,respectively,the morphology of CL-20/binder composite with spherical and good sphericity.Compared with the other two binders,Estane 5703/CL-20 composite showed excellent properties,such as smooth spherical shape with particle size less than 10μm.Compared with raw CL-20,the activation energy of Estane 5703/CL-20 was increased by7.77 k J/mol,T_p0was increased by 4.05℃,the critical temperature of thermal explosion T_bwas increased by 3.71℃,the minimum initiation energy was increased by 250%,and the safety was greatly improved.（3）Finally,CL-20/HMX,CL-20/RDX and CL-20/AP solutions were prepared with acetone as solvent（molar ratios of 2:1,1:1 and 1:1 respectively）,and the CL-20 co-crystal was prepared by spray-drying method accordingly.The results showed that the morphology of CL-20/（HMX,RDX,AP）eutectic was spherical,the particle size was about 5μm,and a new diffraction peak was found in the XRD pattern of eutectic sample,indicating the formation of CL-20 eutectic material.Compared with the raw CL-20,The activation energies of CL-20/HMX and CL-20/AP co-crystal were increased by 32.5 and 52.35 k J/mol,respectively.The critical temperature of thermal explosion T_bwas increased by 0.73 and 9℃,T_p0by 2.03and 10.69℃,respectively,and the minimum initiation energy was increased by 33.33%and46.67%.CL-20/RDX co-crystal showed different thermal decomposition performances from the raw material.DSC showed that there was an endothermic peak near 170℃,and the minimum initiation energy was 44.44%higher than that of the raw material CL-20,indicating that the safety had been improved.