Phase Transition Characteristics And Induction Mechanism Of New High-energy Explosive DATNBI

The energetic crystal is the most core component of the explosive components,and its microstructure largely determines the properties of the explosive components themselves.Under the action of complex environment,it is necessary to have higher structural stability and performance reliability to ensure the long-term safety and effectiveness of weapons in an increasingly complex combat environment.1,1'-diamino-4,4',5,5'-tetranitro-2,2'-biimidazole(DATNBI)was first reported by Breiner in 2013 as a new low-sensitivity high-energy explosive.The energy density of DATNBI is similar to that of HMX,but the sensitivity is lower,which is an ideal substitute.It has been found that there are two crystal forms of?and?in DATNBI,of which the density of?crystal form is up to 1.950 g·cm^-3and the detonation velocity is up to 9129 m·s^-1.Due to the existence of polycrystalline phenomenon,DATNBI will transform to?crystal form at about 140°C,resulting in the deterioration of structure and performance of PBX based on it.At present,it is believed that?-DATNBI(density:1.932 g·cm^-3)will not undergo phase transformation again under thermal stimulation,so the application assessment of?crystal form is focused on.However,will there be no structural phase transition and new crystal form in?crystal under thermal stimulation?What is the thermal expansion characteristics and phase transformation mechanism of DATNBI under thermal stimulation?Is there a good solution to restrain its bad phase transition process?The research on these problems is not clear at present,so this thesis studies the phase transformation characteristics and induction mechanism of DATNBI,so as to have a deeper understanding of the phase transformation process and phase transformation mechanism of DATNBI.It is also helpful to improve the process,performance evaluation and application of DATNBI.The following are the research contents and results of this thesis.(1)It is found for the first time that?and?-DATNBI undergo phase transition under thermal stimulation(before decomposition temperature),forming a new?crystal form,and the phase transition paths are?????and???,respectively,while?-DATNBI does not undergo phase transition before thermal decomposition.Based on in-situ XRD characterization technology,it was found that the cell volume expansion after phase transformation was more than 2.1%,resulting in crystal rupture and forming a large number of small defects.The?crystal after phase transformation still maintains?crystal when it is restored to room temperature and placed for a long time,indicating that it can stably exist at room temperature and atmospheric pressure.(2)From the perspective of cell accumulation,?is a wavy crystal connected by dislocations,?is the alternating accumulation of two different molecular layers to form a wavy crystal,and?is a cross-crossed grid crystal.In the molecular structure of?crystal,the nitro and amino groups deviate from the binary ring greatly,and are not at the same level as the ring,which is also the reason why the phase will not occur again.The structural evolution mechanism of DATNBI was proposed through the understanding of the thermal expansion characteristics of DATNBI and the gradual transition of cell slip to structural phase transition and to the final primary thermal decomposition.(3)According to the calculation results of phase transformation kinetics,the phase transformation activation energy of???process of DATNBI is higher than that of???.Since the activation energy changes with temperature,the phase transformation process is not a one-step reaction,but a complex multi-step reaction.At the same time,the melting and decomposition temperatures of DATNBI prepared by recrystallization were higher than those reported in the literature,indicating that the improvement of crystal quality was helpful to improve the thermal performance and thermal stability of DATNBI.(4)The effect of additives in composite explosives on the phase transformation behavior of?-DATNBI was studied by in-situ XRD.Based on the Rietveld method,the phase transformation law of?-DATNBI in composite explosives was obtained.According to the effect,the additives were divided into three categories:the promotion system,the intermediate system and the inhibition system.The phase transformation process and kinetic mechanism of DATNBI/binder were studied by DSC,and the molecular interaction between DATNBI and binder was studied by Fourier transform infrared spectroscopy,trying to find out the possible reasons for the above effects from the physical and chemical action modes of coating,mixing,and microdissolution.It provides an effective theoretical basis for controlling the phase transition process of DATNBI and reducing the risk of accidental phase transition of DATNBI.This also contributes to the practical application of DATNBI-based explosive composites in military and civilian fields.