CSEDI Collaborative Research: Experimental and Theoretical Investigations on the Elastic and Viscoelastic Properties of Fe-Ni-C Liquids

地核是地球上最遥远、最具活力的部分，由在其中心凝固的液态铁合金组成。地核的性质和动力学与许多地球物理问题密切相关，如地幔对流的驱动力、地球动力学和行星演化。核心主要是铁（Fe）与5-10%的镍（Ni）和一些较轻的元素，如硫(S)、硅（Si）、碳(C)、氧(O)和氢(H)的合金。了解富铁合金和富铁液体在相应堆芯条件下的性能是了解堆芯组成、热态和动力学的前提。与内核的结晶铁合金相比，由于实验的挑战，富铁合金的液体性能数据明显缺乏，这些数据是在远低于外核预期的条件下进行研究的。在可预见的未来，液体性质数据的缺乏和相关核心条件下实验研究面临的巨大挑战预计将继续存在。这促使团队采用协同方法，将实验可实现压力下的实验与核心条件下的计算结合起来。本次合作研究的重点是通过实验和理论的协同作用，研究Fe-Ni-C液体在高压下的弹性和粘弹性特性。这种研究液体性质的方法代表了一种研究极端条件下液体性质的潜在方法，从而推测这种联合努力对类似高压液态物理研究的适用性。提议的研究提供了一个独特的机会，让研究生和本科生在多尺度设施（部门，大学和国家实验室）利用最先进的实验技术和计算工具来解决一个活跃研究领域的基本问题。通过x射线吸收、超声干涉测量、x射线衍射、x射线粘度测定等实验技术，结合计算技术，研究Fe-Ni-C液体在高压下的弹性和粘弹性特性，建立一个关于密度、声速、粘度和液体结构的综合矿物物理数据库，这是以前未知的压力-温度-成分领域。实验数据将为超高压实验数据和理论数据的解释提供重要的基础。低压数据将用于基准测试和验证低压下的理论计算结果，高压计算结果将用于估计和预测岩心条件下的液体性质。这种方法在很大程度上消除了从低压到核心压力的长期外推所引起的错误，并识别了理论计算中的预期偏差。通过实验室实验和理论计算的协同努力，富铁液体的高压-高温行为将有助于提高我们对核心物理和化学的理解。根据这项研究确定的液体性质，将对外核的富碳核心组成模型进行严格的测试。提出的项目的结果，即核心材料的结构、密度、声速和粘度，将成为地球和行星内部碳储层和深层碳循环研究的重要组成部分。新的实验数据也可以很容易地用于讨论行星核心，如月球核心。该团队致力于通过同行评审的期刊出版物传播研究结果，并通过新闻稿、公开讲座和研究网站向当地和更大的社区宣传他们的工作。

The Earth's core, the most remote and dynamic part of our planet, is composed of liquid iron alloys solidified at its center. The nature and dynamics of the core are closely related to manifold geophysical problems such as the driving force of mantle convection, the geodynamo, and planetary evolution. The core is predominantly iron (Fe) alloyed with 5-10% nickel (Ni) and some lighter elements, such as sulfur (S), silicon (Si), carbon (C), oxygen (O), and hydrogen (H). The knowledge of the properties of Fe-rich alloys and liquids under relevant core conditions is a prerequisite for understanding the composition, thermal state and dynamics of the core. In comparison to crystalline iron alloys for the inner core, there exists a remarkable lack of data on liquid properties of iron-rich alloys due to experimental challenges, which have been investigated at conditions far below those expected for the outer core. The lack of data on liquid properties and great challenges facing experimental investigations under relevant core conditions are expected to continue in the foreseeable future. This prompts the team to adopt a synergistic approach by integrating experiments at experimentally-achievable pressures with computations up to core conditions. The focus of this collaborative research will be on the elastic and viscoelastic properties of Fe-Ni-C liquids under high pressures through the synergy between experiment and theory. This approach for investigating liquid properties represents a potential methodology for studying liquid properties under extreme conditions, so as to speculate on the suitability of such combined efforts for similar high-pressure liquid state physics research. The proposed research offers a unique opportunity to engage graduate and undergraduate students to utilize state-of-the-art experimental techniques and computational tools at multi-scale facilities (departmental, university, and national laboratory) for solving fundamental problems in an active research area.The elastic and viscoelastic properties of Fe-Ni-C liquids will be investigated at high pressures by experimental techniques such as X-ray absorption, ultrasonic interferometry, X-ray diffraction, and X-ray viscometry, in combination with computational techniques, to establish a comprehensive mineral physics database on the density, sound velocity, viscosity, and structure of the liquids in a previously uncharted pressure-temperature-composition sector. The laboratory data will provide an important foundation on which the interpretation of ultrahigh pressure laboratory data and theoretical data will be based. The low-pressure data will be used to benchmark and validate results from theoretical calculations at low-pressure, and the higher-pressure calculation results will be used to estimate and predict liquid properties under core conditions. Such a methodology largely eliminates errors often induced in long extrapolations from low-pressure to core pressures, and identifies prospective biases in theoretical calculations. High pressure-temperature behaviors of the iron-rich liquids by the synergistic efforts from laboratory experiments and theoretical calculations will help improve our understanding of the physics and chemistry of the core. Stringent tests of carbon-rich core composition models for the outer core will be performed based on the liquid properties determined from this research. The outcome of the proposed projects, i.e., structure, density, sound velocity, and viscosity of core materials, will become essential parts of the study on carbon reservoirs and deep carbon cycle in the Earth and planetary interiors. The new experimental data could also be readily used in the discussion of planetary cores, such as the lunar core. The team is committed to disseminating the results through peer-reviewed journal publications and to publicizing their work to their local and greater communities through news releases, public lectures, and their research websites.