In Situ X-ray Diffraction Study of Phase Transitions in Shock-Compressed Minerals

冲击压缩矿物相变的原位 X 射线衍射研究

基本信息

批准号：
1644614
负责人：
Thomas Duffy
金额：
$ 47.8万
依托单位：
Princeton University
依托单位国家：
美国
项目类别：
Continuing Grant
财政年份：
2017
资助国家：
美国
起止时间：
2017-01-01 至 2021-12-31
项目状态：
已结题

来源：
https://www.nsf.gov/awardsearch/showAward?AWD_ID=1644614&HistoricalAwards=false
关键词：
Situ ray Diffraction Study Phase

项目摘要

High pressures and temperatures deep within the Earth transform minerals found near the Earth's surface to denser crystalline structures. High density forms of some minerals are also found in trace amounts at the Earth's surface as a result of past meteorite impact events. By impacting minerals with high-speed projectiles in laboratory shock-compression experiments, minerals can be rapidly driven into the high pressure and high temperature conditions occurring deep within the Earth's interior. As such, shock compression experiments have played an important role in earth science for decades by providing insight into the mechanical and acoustic properties of high-pressure minerals. However, past shock compression experiments on minerals have not directly revealed the crystal structures formed during impact and interpretation of shock compression experiments has relied on comparison with results of static high-pressure experiments. In the present research, high-energy synchrotron x-rays will be used during high-speed impact experiments on minerals to directly examine how mineral structures evolve on nanosecond to microsecond timescales during an impact event. The findings will improve our understanding of minerals in the Earth's mantle and will also allow us to better understand the crystal structure modifications occurring in shocked minerals during meteorite impact events. This project will support the training of a graduate student and two undergraduates who will be trained on National synchrotron facilities.This project will be performed at the Dynamic Compression Sector (DCS) at the Advanced Photon Source. The DCS combines a half-inch bore two-stage gas gun capable of launching projectiles with velocities up to 6 km/s with high-energy synchrotron x-ray diffraction capability. Representative minerals such as enstatite, rutile and olivine will be shock compressed via high-speed impact to stresses up to about 60 gigapascals, pressures corresponding to those occurring in large natural meteorite impact events. The velocity histories at the rear surface of the shocked samples will be measured using velocity interferometry; the velocity histories will be analyzed to determine the stress and density of the shocked minerals. Powder x-ray diffraction measurements will also be made on the mineral samples during the impact event using a transmission x-ray geometry in which the incident x-rays pass through the impactor (LiF or polycarbonate), the mineral sample and an x-ray window (LiF or polycarbonate). An x-ray detector will be used to obtain four x-ray diffraction frames (100 picoseconds duration snapshots separated in time by 153.4 nanoseconds) during the impact event. The resulting diffraction patterns will be used to identify the high-pressure mineral structures. Diffraction patterns for shocked single crystal minerals will also be analyzed to understand the high-pressure structure texture which will provide insight into the atomic motions occurring during the structural transformations.

地球深处的高压和高温将地球表面附近发现的矿物转化为更致密的晶体结构。由于过去的陨石撞击事件，在地球表面也发现了一些高密度形式的微量矿物质。通过在实验室冲击压缩实验中用高速射弹撞击矿物，矿物可以被快速驱动到地球内部深处发生的高压和高温条件中。因此，数十年来，冲击压缩实验通过深入了解高压矿物的机械和声学特性，在地球科学中发挥了重要作用。然而，过去对矿物的冲击压缩实验并没有直接揭示冲击过程中形成的晶体结构，并且对冲击压缩实验的解释依赖于与静态高压实验结果的比较。在目前的研究中，高能同步加速器X射线将用于矿物的高速撞击实验，以直接检查撞击事件期间矿物结构如何在纳秒至微秒的时间尺度上演化。这些发现将增进我们对地幔中矿物的了解，并使我们能够更好地了解陨石撞击事件期间受到冲击的矿物中发生的晶体结构变化。该项目将支持一名研究生和两名本科生的培训，他们将在国家同步加速器设施上接受培训。该项目将在先进光子源的动态压缩区（DCS）进行。 DCS 结合了半英寸口径的两级气枪，能够发射速度高达 6 公里/秒的弹丸，并具有高能同步加速器 X 射线衍射能力。顽辉石、金红石和橄榄石等代表性矿物将通过高速撞击而受到冲击压缩，应力高达约 60 吉帕斯卡，该压力相当于大型天然陨石撞击事件中发生的压力。将使用速度干涉测量法测量冲击样品后表面的速度历史；将分析速度历史以确定受冲击矿物的应力和密度。在撞击事件期间，还将使用透射 X 射线几何结构对矿物样品进行粉末 X 射线衍射测量，其中入射 X 射线穿过撞击器（LiF 或聚碳酸酯）、矿物样品和 X 射线窗口（LiF 或聚碳酸酯）。 X 射线探测器将用于在撞击事件期间获取四个 X 射线衍射帧（100 皮秒持续时间快照，时间间隔为 153.4 纳秒）。由此产生的衍射图案将用于识别高压矿物结构。还将分析冲击单晶矿物的衍射图案，以了解高压结构纹理，从而深入了解结构转变过程中发生的原子运动。