高压下含能材料结构稳定性的原位拉曼散射实验与第一性原理计算研究

发布时间：2018-08-18 09:33

【摘要】：材料的结构与性质是凝聚物理学、材料科学、化学等相关领域非常关注的基础问题之一。深入研究物质的微观结构不但有助于我们改善材料的性能而且能够指导我们发展新材料。含能材料在现代国防和民用经济建设中占据重要地位。虽然人类利用含能材料已有数百年历史,但对于其微观结构的稳定性和能量释放机理的研究还相对缺乏。特别是从微观层次认识含能炸药的起爆机理一直是现代爆轰物理、兵器科学、高压凝聚态物理、材料科学等多学科领域共同关注的重要科学问题。含能炸药在点火起爆过程中涉及高温高压环境,经历着复杂的物理、化学变化过程。但从根本上来说,材料的物理和化学性质与其结构息息相关,而研究含能材料在各种加载条件下发生爆炸的微观机理就是要揭示其分子在极端条件下如何发生结构转变或分解反应的问题。另外,研究压力作用下含能材料的分子结构变化对于认识其在起爆过程中的早期反应途径非常有益。因此,开展高压下含能材料的结构及稳定性研究对理解其分解和点火起爆等微观机理方面具有重要的科学意义。基于上述问题,本文采用金刚石压砧(DAC)和轻气炮加载技术,结合原位拉曼光谱技术、冲击热辐射技术以及第一性原理计算方法对几种典型含能材料在高压条件下的结构稳定性进行了研究,具体内容为:首先,研究了硝基苯(NB)在高压下的结构稳定性。硝基苯作为一种结构最为简单的芳香硝基化合物,通常被作为研究硝基苯胺类炸药的模型物质。采用DAC技术和原位拉曼光谱技术,在0-10 GPa压力范围内考察了硝基苯晶体的高压结构与分子振动特性。实验发现,在5 GPa压力附近硝基苯发生了一次结构的突变。为了深入理解实验观测结果,采用基于密度泛函理论(DFT)的第一性原理计算方法对硝基苯在高压下的结构响应行为进行理论模拟研究,计算发现分子键长、键角、二面角等物理参量均在7 GPa压力下发生一个不连续的跳变,预示着硝基苯在高压下发生了结构转变。对照实验和计算结果,我们认为硝基苯分子结构的变化是由于持续增加的压力促使其分子结构扭曲以抵抗增加的相互作用力,继而导致分子结构发生调整;高压下硝基苯拉曼光谱中有限的振动模式发生变化正是由于该分子结构的调整所致。其次,研究了典型的含能材料硝基甲烷(NM)在冲击高压条件下的结构及其稳定性。从微观层面认识含能材料的冲击起爆机理是现代爆轰物理、高压凝聚态物理等多学科领域关注的重要问题之一。我们选取硝基甲烷这一结构最为简单的硝基化合物作为研究对象,基于轻气炮加载平台结合瞬态拉曼散射技术和冲击热辐射原位测量技术,研究了液态炸药硝基甲烷的拉曼特征峰随冲击压力的变化规律和冲击起爆延迟时间。实验结果表明,在冲击起爆前硝基甲烷仍然保持其光学透明特征。获得了硝基甲烷在冲击诱导期间生成新产物的拉曼光谱。首次发现在冲击高压下C-H键率先断裂的实验证据;新的实验结果为研究其他含能材料的点火反应以及冲击起爆机理提供了参考数据。再者,研究了含能晶体1,3-二氨基-2,4,6-三硝基苯(DATB)在高压条件下的结构变化及其稳定性。DATB是硝基苯胺类炸药中一种重要的含能材料,与著名的高钝感炸药TATB的分子结构非常类似,但对其在不同压力下结构及性质的相关研究十分有限。本文采用色散修正密度泛函理论(DFT-D)计算方法,在0-15 GPa压力范围内对DATB晶体的结构及其稳定性进行了研究。结果表明,在常压条件下模拟计算的晶体常数、分子几何结构以及分子间相互作用特征均与实验结果吻合。其次,晶格常数、分子几何结构和弹性常数随压力的变化趋势均在7.5 GPa压力附近发生突变;根据晶体稳定性的力学判据,发现DATB晶体在7.3 GPa左右已不稳定,表明在7.5 GPa压力附近DATB晶体发生了结构失稳。最后,研究了新型含能化合物3,4-二氨基-1,2,4三唑-1-氨基四唑-5-酮(ATO·DATr)在不同压力下的结构稳定性。ATO·DATr具有较高的密度、良好的爆压和爆速,被认为是潜在的钝感含能材料。这类富氮含能化合物由于具有较高的氮元素和生成热,且产物主要是环境友好的氮气等优点而备受关注。本文采用DFT-D计算方法,在0-50 GPa压力范围内研究了 ATO·DATr的晶体结构、状态方程以及电子性质;同时,运用Hirshfeld表面和二维指纹图方法考察了其晶体内分子间相互作用的变化。结果表明,在零压下计算的晶格常数、分子几何结构以及分子间相互作用与实验值相一致。晶体的可压缩性呈现出各向异性并随着压力的增加而减小,ATO · DATr的体积模量也比其他常见含能材料的要高;同时随着压力的增加晶体中的短程相互作用增强,涉及长程相互作用的de值减小,揭示出高压下ATO · DATr晶体可压缩性的减小与分子间相互作用的增强有关。
[Abstract]:Structures and properties of materials are one of the fundamental issues of great concern in condensed physics, material science, chemistry and other related fields. In-depth study of the microstructure of materials can not only help us improve the properties of materials but also guide us to develop new materials. Energetic materials play an important role in modern national defense and civil economic construction. However, it has been hundreds of years since the energetic materials were used by human beings, but the research on the stability of microstructure and the mechanism of energy release is still relatively scarce. The process of ignition and detonation of energetic explosives involves high temperature and high pressure, and undergoes complicated physical and chemical changes. But fundamentally, the physical and chemical properties of materials are closely related to their structures. To study the micro-mechanism of explosion of energetic materials under various loading conditions is to reveal the molecular structure of energetic explosives. In addition, it is very useful to study the molecular structure changes of energetic materials under pressure for understanding the early reaction pathways in the initiation process. Therefore, the study on the structure and stability of energetic materials under high pressure is helpful to understand the micro-machine such as decomposition and ignition initiation. Based on the above problems, the structural stability of several typical energetic materials under high pressure is studied by means of diamond anvil (DAC) and light gas gun loading technique, in situ Raman spectroscopy, thermal shock radiation technique and first-principles calculation method. The structure stability of nitrobenzene (NB) at high pressure has been studied. Nitrobenzene, as the simplest aromatic nitro compound, is usually used as a model material for the study of nitroaniline explosives. The high pressure structure and molecular vibration of NB crystals have been investigated by using DAC and in situ Raman spectroscopy in the pressure range of 0-10 GPa. In order to understand the experimental results, the first-principles calculation method based on density functional theory (DFT) was used to simulate the structure response behavior of nitrobenzene at high pressure. The molecular bond length, bond angle and dihedral angle were found. A discontinuous jump of physical parameters at 7 GPa pressures indicates a structural transition of nitrobenzene at high pressures. Contrasting the experimental and computational results, we believe that the change of the molecular structure of nitrobenzene is attributed to the continuous increase of pressure which leads to the distortion of its molecular structure to resist the increasing interaction force, and then leads to the molecular structure. Secondly, the structure and stability of a typical energetic material, nitromethane (NM), under shock high pressure were studied. The shock initiation mechanism of energetic materials was recognized as modern detonation physics from the microscopic level. The Raman characteristic peaks of liquid explosive nitromethane have been studied based on the light gas gun loading platform combined with the transient Raman scattering technique and the shock thermal radiation in situ measurement technique. The experimental results show that the optical transparency of nitromethane is maintained before shock initiation. Raman spectra of new products of nitromethane during shock induction are obtained. Furthermore, the structural changes and stability of energetic crystals 1,3-diamino-2,4,6-trinitrobenzene (DATB) under high pressure were studied. DATB is an important energetic material in nitroaniline explosives, and the molecule of famous highly insensitive explosive TATB. The structure of DATB crystals is very similar, but the research on the structure and properties of DATB crystals under different pressures is very limited. In this paper, the structure and stability of DATB crystals are studied in the pressure range of 0-15 GPa by using the dispersion-corrected density functional theory (DFT-D). Secondly, the lattice constants, molecular geometric structures and elastic constants change abruptly near 7.5 GPa pressure. According to the mechanical criterion of crystal stability, it is found that DATB crystal is unstable around 7.3 GPa, indicating that DATB crystal is unstable near 7.5 GPa pressure. Finally, the structural stability of a new energetic compound 3,4-diamino-1,2,4-triazole-1-aminotetrazole-5-one (ATO.DATr) at different pressures was studied. ATO.DATr is considered as a potential insensitive energetic material because of its high density, good detonation pressure and detonation velocity. In this paper, the crystal structure, equation of state and electronic properties of ATO DATr have been studied by DFT-D method in the pressure range of 0-50 GPa. The results show that the lattice constants, molecular geometry and intermolecular interactions calculated at zero pressure are consistent with the experimental values. The compressibility of the crystals is anisotropic and decreases with the increase of pressure. The bulk modulus of ATO. DATr is also higher than that of other energetic materials. The short-range interaction in the crystal is enhanced, and the de value involved in the long-range interaction decreases. It is revealed that the decrease of compressibility of ATO.DATr crystal under high pressure is related to the enhancement of intermolecular interaction.
【学位授予单位】：西南交通大学
【学位级别】：博士
【学位授予年份】：2017
【分类号】：TB34

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