CSEDI Collaborative Research: Electrical and Thermal Transport in Iron and Iron Alloys at Core Conditions and its Effects on the Geodynamo and Thermal Earth History

地球和其他行星体的磁场是由导电流体在其内部深处的湍流产生的。在地球上，它是由外核产生的，外核由液态铁和一些镍和轻元素组成。地球的磁场很重要，因为如果没有它对太阳风的屏蔽，生命可能不会存在。此外，核心上升的热量助长了地幔的热对流，这是板块构造和相关灾害的起因。要了解地球磁场和地核热流，需要详细了解在地核极端压力和温度下富铁物质的性质。然而，现有的实验数据和理论计算是不一致的。在这里，多学科团队研究了铁合金在极端条件下的导热和导电性。他们使用了原子尺度和核心尺度的最先进的实验、理论和建模的组合。预期的结果应该与地核的热传输和磁场演化的实验和建模相一致。该项目支持矿物物理领域的一名研究生和两名博士后助理。它对地磁学、地球动力学和地震学有很强的影响，对材料科学也有广泛的影响。高压和高温实验是在激光加热的金刚石压腔中进行的。极端的压力和温度产生在两个相对的钻石的尖端，也就是放置铁样的地方。该团队将在与堆芯相关的条件下测量和计算电导率和热导率。这使得他们能够测试Wiedemann-Franz定律在这些条件下的适用性。这一经验定律将金属的导热系数和电导系数联系起来。在这里，电导率是使用从电池外部引出的四个探头电连接来测量的。结合脉冲激光加热和模化，用光学光谱辐射法测量导热系数。用第一性原理量子力学模拟了类似的条件，计算了液态铁和固态铁的电导率和热导率，并与实验观测结果进行了比较。这些计算是困难的，因为它们涉及电子相互散射以及流体或固体中运动的原子的散射。实验和理论结果被用于堆芯冷却和磁场产生的地球物理模型。这将允许更好地限制地球磁场的历史和核-地幔边界的热流。这一奖项反映了NSF的法定使命，并通过使用基金会的智力优势和更广泛的影响审查标准进行评估，被认为值得支持。

The magnetic field of the Earth and other planetary bodies is generated by the turbulent flow of conducting fluids in their deep interiors. In the Earth, it is generated by the outer core, made of liquid iron with some nickel and light elements. Earth's magnetic field is important, as life may not exist without its shielding of the solar wind. Moreover, the heat rising from the core fuels mantle thermal convection, at the origin of plate tectonics and associated hazards. Understanding Earth's magnetic field and core heat flow requires detailed knowledge of iron-rich material properties at the extreme pressures and temperatures of the core. Yet, existing experimental data and theoretical calculations are inconsistent. Here, the multidisciplinary team investigates the thermal and electrical conductivities of iron alloys at extreme conditions. They use a combination of state-of-the-art experiments, theory, and modeling at both the atomic scale and the scale of the core. Expected results should reconcile experiments and modeling of the core's heat transport and magnetic field evolution. This project supports one graduate student and two postdoctoral associates in the field of Mineral Physics. It has strong implications for Geomagnetism, Geodynamics and Seismology, and broad impacts in Materials Science.High-pressure and temperature experiments are carried out in the laser-heated diamond anvil cell. Extreme pressures and temperatures are generated at the tips of two opposing diamonds, where the iron sample is placed. The team will measure and compute electrical and thermal conductivities at conditions relevant to the core. This allows them to test the applicability of the Wiedemann-Franz law at these conditions. This empirical law relates thermal and electrical conductivities in metals. Here, the electrical conductivity is measured using a four-probe electrical connection brought outside from the cell. Thermal conductivity is measured by optical spectroradiometry in conjunction with pulsed-laser heating and modeling. Similar conditions are simulated using first-principles quantum mechanics to compute the electrical and thermal conductivity in liquid and solid iron, and compare them with experimental observations. These calculations are difficult because they involve the scattering of electrons off each other and off the moving atoms in the fluid or solid. Experimental and theoretical results are used in geophysical models of core cooling and magnetic field generation. This will allow to better constrain the history of Earth's magnetic field and the heat flow at the core-mantle boundary.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.