X-ray Scattering Experiments on Melting and Equations of State of Candidate Compositions of Earth's Core

这个项目的预期结果将提高我们对地核温度和化学成分的了解。众所周知，地球的核心是一种富含铁的合金，大部分是熔融的，但内核是坚固的。除了铁，它还含有大约5%的镍和大约10%的较轻元素，其身份尚不确定，但很可能是氧、硫、硅和/或碳的组合。更准确地了解地核的组成，对于限制我们对导致地球形成的化学和物理过程的理解是重要的。此外，地球深处的温度结构知之甚少，在相关的压力和温度条件下，通过更准确地测量候选岩芯成分的熔融温度，可以更好地约束这种结构。因此，该项目的目标是测量在极端压力下铁合金的熔化温度和密度，即地核中存在的温度条件。实验结果将被用来对地核的温度和成分设定更准确的界限。该项目有几个具体的实验研究目标。这些措施包括(1)确定Fe-O-S、Fe-Si-S和Fe-Si-O三元系统的熔化温度，直到地球外核适当的压力；(2)分析从这些三元系统熔体测量的X射线漫散射，以对其液体密度施加约束；(3)将Fe3C和Fe3S的状态方程扩展到更高的压力和温度条件，以便对S和含碳铁合金进行更精确的热力学处理，并对地核允许的S和C的最大含量进行更精确的密度约束。为了实现这些目标，PI将对在钻石顶压室中加压和激光加热的样品进行基于同步加速器的X射线散射实验，达到地球核心中存在的极端压力和温度条件(超过140 GPA和4000 K)。在这些研究的同时，他将继续开发实验方法，以提高他的实验室和其他实验室调查地核材料属性的能力。这些研究项目也将作为一个平台，在这个平台上，PI对研究生和本科生的培训将在实验室研究和科学追求方面进行。

The results expected from this project will improve our understanding of the temperature and chemical composition of Earth's core. Earth's core is known to be an iron-rich alloy, mostly molten but with a solid inner core. In addition to iron it contains approximately 5% nickel and approximately 10% of a lighter element, whose identity is uncertain but is likely a combination of oxygen, sulfur, silicon, and/or carbon. A more precise understanding of the composition of Earth's core is important to constrain our understanding of the chemical and physical processes that led to the formation of our planet. Furthermore, the temperature structure in the deep Earth is poorly known, and can be better constrained with more accurate measurements of the melting temperatures of candidate core compositions under the relevant pressure, temperature conditions. Accordingly, the aims of this project are to measure the melting temperatures and densities of iron alloys under the extreme pressure, temperature conditions that exist in Earth's core. The experimental results will be applied to place more accurate bounds on the temperatures and composition of Earth's core.The project has several specific experimental research goals. These include (1) Establishing melting temperatures in the ternary systems Fe-O-S, Fe-Si-S, and Fe-Si-O up to pressures appropriate in Earth's outer core; (2) Analyzing X-ray diffuse scattering measured from melts in these ternary systems to place constraints on their liquid densities; (3) Extending the equations of state of Fe3C and Fe3S to higher pressure and temperature conditions, to permit more precise thermodynamic treatment of S,C-bearing Fe-alloys, and more precise density-based constraints on the maximum content of S and C allowable in Earth's core. To achieve these goals the PI will perform synchrotron-based X-ray scattering experiments on samples that are pressurized and laser heated in a diamond anvil cell, reaching the extreme pressure, temperature conditions (in excess of 140 GPa and 4000 K) that exist in Earth's core. In parallel with these investigations, he will continue to develop experimental methods to improve the ability of his lab and others to investigate the material properties of Earth's core. These research projects will also serve as a platform on which the PI's training of graduate and undergraduate students will be trained in laboratory research and scientific pursuit.