冲击动态加载下水的瞬态拉曼光谱与亚稳态结构研究

发布时间：2018-03-07 15:42

  本文选题：冲击加载　切入点：亚稳态冰　出处：《西南交通大学》2015年博士论文　论文类型：学位论文

【摘要】：水是自然界最丰富的物质之一,有重要的工业和国防应用。单个水分子(H20)结构虽然简单,但它的凝聚态形式却十分复杂。人们已经发现在静态高压下水可以转化为十几种不同结构形式的冰相,却对在冲击动态加载过程中水的结构演变特征了解甚少。冲击波加载过程发生在纳秒时间尺度,在此过程体系的温度和压强变化的速率可能远远超过结晶相变的速率,以致人们所预期的某些结晶过程可能还没来得及发生,体系的结构将直接演变到某些亚稳态形式。在动态加载过程中水的结构演变途径将对其冲击动力学性质产生重要影响,在设计海洋水下目标的攻击和防护方案时水的动力学特征是必要的物理与力学参量。最近人们研究了水在等熵加载和准等熵加载(多次冲击加载)过程中的动力学行为和光学透明特性,揭示了水在冲击波诱导下的结晶现象和相变动力学弛豫现象。但是,有关冲击波诱导产生的高压相冰的微观结构和光谱特性研究还是空白,因而关于水的冲击结晶相的具体结构目前仍然还仅是一种推测。瞬态拉曼光谱技术是探测冲击波诱导物质结构相变的最理想实验手段,然而水分子的拉曼散射截面非常小,其拉曼信号十分微弱。多年来,这个技术瓶颈一直没有新突破,该科学问题的解决面临挑战。本文发展了一种气炮加载冲击瞬态拉曼光谱技术,提高了时间控制精度和灵敏度,使其能够跟踪多次冲击加载过程并分辨出体系中更丰富的光谱特征。在此基础上,结合轻气炮快速加载手段、瞬态拉曼原位光谱技术以及从头计算分子动力学模拟方法,在探索冲击高压下条件水的微观结构、振动频谱和分子间氢键变化规律方面取得了一些新的结果：(1)采用冲击-再冲击加载技术,首次在冰Ⅶ熔化线两侧的温度和压强条件下获得了水的冲击瞬态拉曼散射光谱；(2)在冲击加载条件下首次观测到水拉曼散射光谱中位于低波段的成分明显增加,证实再冲击加载体系中的氢键效应增强；(3)首次在冰Ⅶ相稳定的温压区获得水的冲击瞬态拉曼散射光谱,发现冲击波诱导结冰过程所生成的新相不同于冰Ⅶ相,而是一种亚稳相高压冰结构；(4)采用从头计算分子动力学模拟方法,在与冲击加载实验相近的温度和压强区域获得了一种具有无定形结构的高压冰相,发现该冰相的模拟振动谱与冲击-再冲击状态水的实测拉曼散射光谱轮廓相似,在光谱展宽方面也相似；(5)采用从头计算分子动力学模拟方法,首次揭示出O-H振动频谱与体系中局域氢键键长分布间存在关联性,并支持局域氢键环境不对称导致分子两支内O-H伸缩振动谱不对称这一观点。
[Abstract]:Water is one of the most abundant substances in nature and has important industrial and national defense applications. But its condensed form is very complicated. It has been found that at static high pressure water can be converted into a dozen different structural forms of ice, However, very little is known about the structural evolution of water during dynamic impact loading. The shock wave loading occurs on a nanosecond time scale, and the rate of temperature and pressure changes in this process may be much higher than the rate of crystallization phase transition. As a result, some of the expected crystallization processes may not take place in time, and the structure of the system will directly evolve to some metastable state. During dynamic loading, the evolution of water structure will have an important effect on its impact dynamic properties. The dynamic characteristics of water are necessary physical and mechanical parameters in designing attack and protection schemes for underwater targets. Recently, the dynamic behavior of water in isentropic loading and quasi-isentropic loading (multiple shock loading) has been studied. Academic behavior and optical transparency, The phenomena of crystallization and phase transition dynamics relaxation of water induced by shock wave are revealed. However, the study on the microstructure and spectral characteristics of high-pressure phase ice induced by shock wave is still blank. Therefore, the specific structure of the impact crystalline phase of water is still only speculated. Transient Raman spectroscopy is the most ideal experimental means to detect the structural phase transition induced by shock wave, but the Raman cross section of water molecule is very small. The Raman signal is very weak. For many years, there has been no new breakthrough in this technical bottleneck, and the solution of this scientific problem is facing a challenge. In this paper, a gas gun loaded shock transient Raman spectroscopy technology is developed, which improves the time control accuracy and sensitivity. On the basis of this, the transient Raman in-situ spectroscopy and ab initio molecular dynamics simulation are combined with the rapid loading method of light gas gun, the transient Raman in-situ spectroscopy and the ab initio molecular dynamics simulation. Some new results have been obtained in exploring the microstructure, vibrational spectrum and intermolecular hydrogen bond variation of water under shock pressure. Under the condition of temperature and pressure on both sides of the melting line of ice 鈪，

本文编号：1579911