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理解。众所周知，地核是一种富含铁的合金，大部分是熔融的，但内核是固体的。除了铁，它还含有大约5%的镍和大约10%的轻元素，这种轻元素的性质尚不确定，但可能是氧、硫、硅和/或碳的组合。更精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很重要的。此外，我们对地球深处的温度结构知之甚少，在相应的压力、温度条件下，对候选岩心成分的熔化温度进行更精确的测量可以更好地约束这些结构。因此，该项目的目的是测量铁合金在地核极端压力和温度条件下的熔化温度和密度。实验结果将用于对地核的温度和组成进行更精确的界定。该项目有几个具体的实验研究目标。这些措施包括：(1)将Fe-O-S、Fe-Si-S和Fe-Si-O三元体系的熔化温度提高到适合地球外核的压力；(2)分析这些三元体系中熔体的x射线漫射散射，以确定其液体密度的约束条件；(3)将Fe3C和Fe3S的状态方程扩展到更高的压力和温度条件下，以便对含S和C的铁合金进行更精确的热力学处理，并对地核中允许的S和C的最大含量进行更精确的基于密度的约束。为了实现这些目标，PI将对在金刚石砧细胞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，达到地核中存在的极端压力和温度条件（超过140 GPa和4000 K）。在进行这些研究的同时，他将继续开发实验方法，以提高他的实验室和其他实验室研究地核物质特性的能力。这些研究项目也将成为学院培养研究生和本科生进行实验室研究和科学追求的平台。

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.