Experimental Investigations of Carbon in Earth's Core

地球中碳的实验研究的核心智力价值。 以前的研究提出，全球碳循环涉及Fe3C或Fe7C3作为地球固体部分的主要成分？的核心，即使关键的数据来测试的假设，碳化物丰富的内核仍然失踪。Fe-C二元系相关系的实验结果限制在70GPa。声速数据仅适用于Fe3C，在300 K时高达68 GPa，高温时高达47 GPa。Fe3C的密度测量在压力下达到~200 GPa，但高温数据很少。特别是，需要实验来评估70 GPa附近的磁性转变对碳化铁的热弹性和振动特性的影响，并量化温度对其磁性，密度和声速的影响。建议使用多对顶砧和金刚石对顶砧压力装置来研究高达核心压力区和~3000 K的碳化铁的压缩和熔化行为。具体目标包括：[1]采用核共振散射法测定了Fe3C和Fe7C3的偏声子密度;[2]采用同步辐射X射线衍射法建立了Fe3C和Fe7C3的热物态方程;[3]采用原位X射线衍射和聚焦离子束FIB淬火分析相结合的方法测定了Fe-C二元系的共晶成分。拟议的活动将提供关于候选碳化铁与堆芯压力和高温的相位关系、密度和声速的新数据，从而能够对以碳为主要成分的内核模型进行严格的测试。预期的结果将促进我们对地球的了解？地球深部碳循环是固体地球研究中的一个中心和及时的问题。这些研究将通过阐明磁体积和非谐性在潜在核心材料的热力学和晶格振动中的作用，为核心化学的最终模型奠定基础。对核心碳含量的关键限制将补充地球化学，地震学和地球动力学研究，以扩大地球深部研究的前沿。这项工作也将有助于天体物理学和行星科学的碳从星星诞生到行星分化的途径，以及材料科学和凝聚态物理学的碳基材料和极端环境下的强相关系统的行为。更广泛的影响。 首席PI致力于通过课程设置，讲座和辅导课程（例如，密歇根数学和科学学者计划和动力地球研究暑期学校合作研究所）。拟议的实验将培养一名研究生在美国国家实验室的高压研究实验室中使用最先进的实验技术来解决基础科学问题。密歇根州和先进光子源（APS）在阿贡国家实验室（ANL）。拟议的活动将通过区域和国家设施的合作项目，包括地球物理实验室，APS和国家纳米技术基础设施网络（NNIN），加强研究和教育的基础设施。该项目将为社区提供校准标准，以支持与碳有关的研究。该提案将涉及女性研究人员，并为陈博士作为新的PI提供部分支持。研究所将继续积极通过出版物、国家和国际会议、互联网和新闻媒体广泛传播研究成果。

Experimental Investigations of Carbon in Earth?s Core Intellectual merit. Previous studies proposed that the global carbon cycle involved Fe3C or Fe7C3 as a dominant component in the solid portion of Earth?s core, even though critical data to test the hypothesis of carbide-rich inner core are still missing. Experimental results on the phase relation of the Fe-C binary system are limited to 70 GPa. Sound velocity data are only available for Fe3C, under conditions up to 68 GPa at 300 K and up to 47 GPa at high temperatures. Density measurements on Fe3C have reached ~ 200 GPa in pressure, but high temperature data are scarce. In particular, experiments are needed to assess the effects of magnetic transition near 70 GPa on the thermoelastic and vibrational properties of the iron carbides, and to quantify the influence of temperature on their magnetism, density and sound velocities. It is proposed to investigate the compression and melting behavior of iron carbides up to the core pressure regime and ~ 3000 K using multi-anvil and diamond anvil cell pressure devices. Specific goals include: [1] determine the partial phonon density of Fe3C and Fe7C3 using the nuclear resonant scattering method; [2] establish the thermal equation of state of Fe3C and Fe7C3 using the synchrotron X-ray diffraction methods; [3] determine the eutectic composition of the Fe-C binary system using a combination of in situ X-ray diffraction and focused ion beam FIB-based quench analysis methods. The proposed activities will provide new data on the phase relations, densities, and sound velocities of candidate iron carbides to core pressures and high temperatures, thus enabling a stringent test of inner core models involving carbon as a major component. The expected results will advance our understanding of Earth?s deep carbon cycle, a central and timely issue in solid Earth research. The investigations will establish stepping-stones toward an ultimate model of core chemistry by elucidating the role of magneto-volume and anharmonicity in the thermodynamics and lattice vibration of potential core materials. Key constraints on the carbon content of the core will complement geochemical, seismological, and geodynamic studies to expand the frontier of deep Earth research. This work will also contribute to astrophysics and planetary science on the pathways of carbon from star birth to planet differentiation, and to materials science and condensed-matter physics on the behavior of carbon-based materials and strongly correlated systems under extreme environments. Broader impact. The lead PI is committed to teaching and training at high school to postdoctoral levels through course offerings, lectures, and tutorial sessions (e.g., for the Michigan Math and Science Scholar program and at the Cooperative Institute for Dynamic Earth Research Summer Schools). The proposed experiments will train a graduate student to tackle fundamental scientific problems using the state-of-the-art experimental techniques in the high-pressure research laboratories at U. Michigan and the Advanced Photon Source (APS) at the Argonne National Laboratory (ANL). The proposed activity will enhance the infrastructure for research and education through collaborative projects at regional and national facilities including the Geophysical Laboratory, APS, and National Nanotechnology Infrastructure Network (NNIN). The project will produce calibration standards for the community to support carbon-related research. The proposal will involve female researchers and provide partial support for Dr. Chen as a new PI. The PIs will continue to actively disseminate research results broadly through publications, national and international meetings, the Internet, and news media.