| Temperature and pressure are two important parameters that control the structure and properties of materials,as well as the necessary extreme conditions that energetic materials need to experience before detonation and ignition.Explosive explosion is an ultra-fast and damaging process,and an alternative way to understand the initiation reaction process from the atomic and molecular scale is to statically load the high temperature/pressure encountered in the process of the shock wave generation.And to study its effect on the unreacted energetic materials,so that experimental observations can be carried out on a longer time scale,making it possible to measure various physical and chemical properties of energetic materials under high temperature and high pressure.In this thesis,we selected research subjects that the representative of insensitive explosives TATB crystal and the representative of energy explosives CL-20 crystal in traditional energetic materials,CL-20/DNB cocrystal and CL-20/CO2 host-guest explosive in novel energetic materials,and systematically studied their structural evolution,the law of crystal form transition,stability,chemical decomposition reaction,temperature-pressure phase diagram,and the light absorption phenomenon,etc.The present thesis consists of six chapters,and its contents are as follows:In the first chapter,the development of high-pressure science and technology,the experimental technology of diamond anvil cells,the technical means and application fields of high-pressure research,and the research status of energetic materials under high pressure are introduced.In the second chapter,the effect of high pressure on the conformational changes and electronic structure of the energetic material TATB is systematically studied.Using experimental methods,such as Raman,absorption and synchrotron radiation x-ray diffraction,combined with first-principles calculations,the mechanism of discoloration of TATB samples is explained.The study find that near the pressure of 5 GPa,TATB has a conformational transition,which involves the rotation of the nitro and amino groups relative to the benzene ring plane,and is accompanied by the color’s changes of the sample from yellow to red and the red shift of the absorption edge.At the same time,the third-order Birch-Murnaghan equation of state（EOS）for TATB is obtained in the pressure range of 16.5 GPa.In addition,we discussed the stability at low temperature and thermal decomposition behavior at high temperature of TATB.Simultaneously,we added two parameters,temperature and pressure,to study its thermal decomposition under high pressure.The results indicate that pressure can hinder the process of decomposition reaction of TATB and have a great influence on its decomposition temperature.In the third chapter,the law of conversion for different crystal forms,structural evolution and temperature-pressure（T-P）phase diagram of high-energy explosive CL-20 under extreme conditions of high temperature and high pressure are systematically studied.The study finds that the ε→γ phase transition,accompanied by a 6-7%volume mutation,occurs in the temperature range of 145-165℃.The γ phase is the most stable phase at high temperature and maintains the structural stability until it decomposes during the process of loading temperature.In addition,a systematic study of structural evolution and the route of phase transition for ε-CL-20 and γ-CL-20 are performed under quasi-hydrostatic pressures of up to 60 GPa.The research results show that when the initial phase is ε phase,it will go through the following phase transition process:ε→γ’（0.9～4.4 GPa）,γ’→η（6.9～10.6 GPa）,η→φ（28 GPa）and φ→ι（50.5 GPa）.However,with the y phase as the initial phase,the process of γ-ζ phase transition is only observed near the pressure of 1.3 GPa,and the ζ phase maintains its structural stability with continued pressurization until 47.4 GPa.Meanwhile,we compare the different paths of phase transition for newly discovered γ’ phase in the experiment and γ phase under high pressure,and finally summarize the temperature-pressure phase diagram for CL-20 of different crystal forms.In the fourth chapter,the phase transition and thermal decomposition process of the novel energetic material CL-20/DNB cocrystal under high temperature conditions,as well as the structural stability and light absorption phenomena under high pressure conditions,are studied.The research results present that the CL-20/DNB cocrystal has an endothermic phenomenon in the temperature range of 120～130℃,which corresponds to the melting process of the DNB single-component.In the meantime,the process of β→γ phase transition for CL-20 single-component is observed.Under pressure loading,the synchrotron radiation x-ray diffraction results demonstrate that the cocrystal sample has a significant structural phase transition near 14 GPa,which results in the changes in the color of the sample and a notable red shift of the absorption edge.In the fifth chapter,a novel α-CL-20/CO2 explosive with host-guest structure is prepared using high-pressure physical methods to embed small molecular gas CO2 in the lattice of high-energy caged explosive CL-20.And its structure and morphology are characterized.The law of structural evolution and high-pressure stability of the host-guest explosive are studied in-depth.It is found that its stability under high pressure is far better than that of CL-20 crystals without small molecules embedded.In the sixth chapter,we gave a summary of the research contents of this thesis. |
