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其内部深处导电流体的湍流产生的。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。地球磁场很重要，因为如果没有太阳风的屏蔽，生命就不可能存在。此外，从地核升起的热量会引发地幔热对流，这是板块构造和相关危险的根源。了解地球磁场和地核热流需要详细了解地核极端压力和温度下富铁材料的特性。然而，现有的实验数据和理论计算并不一致。在这里，多学科团队研究了极端条件下铁合金的导热性和导电性。他们在原子尺度和核心尺度上结合了最先进的实验、理论和建模。预期结果应该协调核心热传输和磁场演化的实验和建模。该项目支持矿物物理学领域的一名研究生和两名博士后。它对地磁学、地球动力学和地震学具有重要意义，并对材料科学产生广泛影响。高压和高温实验是在激光加热金刚石砧室中进行的。 放置铁样品的两颗相对的钻石的尖端会产生极高的压力和温度。该团队将测量和计算与核心相关的条件下的电导率和热导率。这使他们能够测试维德曼-弗朗茨定律在这些条件下的适用性。该经验定律与金属的导热性和导电性相关。这里，使用从电池外部引出的四探针电连接来测量电导率。热导率通过光学光谱辐射测量结合脉冲激光加热和建模来测量。使用第一原理量子力学模拟类似的条件，计算液态和固态铁的电导率和热导率，并将其与实验观察结果进行比较。这些计算很困难，因为它们涉及电子相互散射以及流体或固体中移动原子的散射。实验和理论结果用于岩心冷却和磁场生成的地球物理模型。 这将能够更好地限制地球磁场的历史和地核-地幔边界的热流。该奖项反映了 NSF 的法定使命，并通过使用基金会的智力价值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.