Melting Studies of Core-forming Alloys

该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，地球的核心是一种富含铁的合金，大部分是熔融的，但有一个固体内核。除了铁，它还含有约5%的镍和约10%的较轻元素，其身份不确定，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更好地推断导致我们星球形成的化学和物理过程非常重要。对这个问题的一个未充分利用的约束是固体内芯与液体外芯边界处的密度对比，其中固化已经随着时间发生。这种密度差异，由地震学研究确定为约7%，意味着固体和液体之间的实质性成分差异，并且不容易通过相关富铁系统的现有相图来满足。然而，人们对这些相图知之甚少，因此，本项目的目的是通过测量在地球核心存在的极端压力和温度条件下共存的固体和液体铁合金的成分来获得它们。实验结果将被应用于地球核心组成的更精确的界限。该研究项目还将作为培养研究生和本科生进行高级实验室研究和科学追求的平台。该项目的具体实验研究目标是测量Fe-O-S系统中的固体/熔体相关系，其压力和温度与地球内部深处的压力和温度相当（即超过200 GPa和4000 K），使用激光加热金刚石砧座技术。实验将在芝加哥大学矿物物理实验室进行。将使用聚焦离子束（FIB）和扫描电子显微镜（SEM）进行样品提取和微量分析。根据需要，还可以通过透射电子显微镜（TEM）检查选定的样品。测得的共存的液相和固相的组成将被用来构建富铁合金系统的相图。为了增强实验，结果将用于指导合金系统的热力学描述;这将最大限度地减少所需实验的数量，并提供一个框架，用于将结果外推/内插到未通过实验直接研究的压力-温度-组成点。

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 deduce better the chemical and physical processes that led to the formation of our planet. An underutilized constraint on this problem is the density contrast at the solid inner core to liquid outer core boundary, where solidification has taken place over time. This density difference, determined by seismological studies to be approximately 7%, implies a subtantial compositional difference between the solid and liquid, and is not easily satisfied by existing phase diagrams of the relevant iron-rich systems. These phase diagrams are poorly known, however, and accordingly, the aims of this project are to obtain them by measuring the compositions of coexisting solid and liquid iron alloys under the extreme pressure, temperature conditions that exist in Earth's core. The experimental results will be applied to place more precise bounds on the composition of Earth's core. This research project will also serve as a platform for the training of graduate and undergraduate students in advanced laboratory research and scientific pursuit.The specific experimental research goals of this project are to measure the solid/melt phase relations in the Fe-O-S system up to pressures and temperatures comparable to those in Earth's deep interior (i.e. exceeding 200 GPa and 4000 K), using laser heated diamond anvil cell technology. The experiments will be performed in the Laboratory for Mineral Physics at the University of Chicago. Sample extraction and microanalysis will be performed using focused ion beam (FIB) and scanning electron microscopy (SEM). Selected samples may also be examined by transmission electron microscopy (TEM) as needed. The measured compositions of coexisting liquid and solid phases will be used to construct phase diagrams for the Fe-rich alloy systems. To augment the experiments, the results will be used to guide a thermodynamic description of the alloy systems; this will minimize the number of experiments needed as well as provide a framework for extrapolating / interpolating the results to pressure-temperature-composition points that are not directly studied by experiment.