Thermal Safety Evaluation Of CL-20 Based Co-crystal Explosives Based On Thermal Decomposition Kinetics

In the field of energetic materials,the successful application of co-crystal technology has opened up a new way for the study of sensitization reduction of CL-20.In recent years,several excellent CL-20 based co-crystal explosives have been successfully prepared by researchers.However,experimental studies on thermal decomposition of CL-20 based co-crystal are still rare.In order to promote the application of CL-20 based co-crystal explosive in future engineering amplification and later stage stereotyping,thermal hazard assessment needs to be studied urgently.In this paper,two typical new co-crystal explosives,CL-20/HMX and CL-20/BTF co-crystal,are selected as research objects;the research is carried out by means of DSC,in-situ IR,in-situ XRD and ARC-GC-MS;the thermal decomposition kinetics model of CL-20/HMX,CL-20/BTF co-crystal was established by using nonlinear optimization fitting method;thermal decomposition mechanism,thermal safety performance and storage life of CL-20-based co-crystal explosives?CL-20/HMX,CL-20/BTF co-crystal?were studied which based on the established decomposition kinetics model.The specific research contents are as follows:1.Study on thermal properties of co-crystal explosives:using DSC,ARC,etc.,to study the characteristic parameters such as crystal transformation temperature,melting point,initial decomposition temperature,termination temperature,peak temperature,decomposition enthalpy.2.Study on thermal decomposition kinetics of co-crystal explosives:Based on the above thermal characteristic parameters,thermal decomposition kinetics model was established to obtain the thermal decomposition kinetics parameters of co-crystal explosives,such as activation energy E_a,pre-exponential factor A,thermal decomposition mechanism function????,etc.3.Study on thermal decomposition mechanism of co-crystal explosives:Real-time acquisition of thermal decomposition gas products by means of in-situ thermal analysis such as ARC-GC-MS;In-situ spectral techniques such as in-situ IR were used to obtain structural evolution information of co-crystal explosives,such as molecular groups and molecular skeletons.Thereby,the characteristics of thermal decomposition and its internal mechanism can be systematically studied.4.Study on thermal safety performance of co-crystal explosives:Based on thermal decomposition kinetics model,the storage of 5 kg,20 kg,50 kg,150 kg CL-20/HMX co-crystal explosives and CL-20/BTF co-crystal explosives at constant ambient temperature were calculated and simulated.By evaluating the storage safety of large quantities of co-crystal explosives under different conditions,the typical thermal safety parameters of co-crystal explosives were obtained and assessing their aging life.It is found that the thermal decomposition process of CL-20/HMX co-crystal and CL20/BTF co-crystal is a two-step parallel complex autocatalytic reaction,and the two parallel reaction paths are competitive and dominant in the thermal decomposition process,and their contribution to the total reaction varies with the heating rate of DSC;the simulated isothermal prediction experiments of CL-20/HMX co-crystal and CL-20/BTF co-crystal and the critical temperature of 1000^th second thermal explosion are in good agreement with the experimental results,which proves the accuracy of the thermal decomposition kinetic model.On this basis,typical thermal safety parameters of CL-20/HMX co-crystal and CL-20/BTF co-crystal were obtained,such as T_d,24,SADT,emergency temperature and controllable temperature.In addition,a deeper understanding of thermal decomposition process of CL-20 and CL-20/HMX co-crystals at the molecular level?chemical structure?has been gained.It is found that the infrared absorption characteristics of the inner and outer groups of the molecular skeleton of CL-20 and CL-20/HMX co-crystal undergo a multi-stage change process with increasing temperature.The outer groups of the molecular skeleton are more sensitive to temperature and respond earlier than the inner groups of the skeleton.During the heating process of CL-20,the C-C stretching vibration appears a new infrared characteristic peak which is closely related to crystal transformation of CL-20??-??.Moreover,the change of C-C stretching vibration mode in the skeleton did not stop until the end of thermal decomposition of CL-20;during the heating process of CL-20/HMX co-crystal,the-NO₂ group outside the molecular skeleton might first break off.