Collaborative Research: CSEDI--First Principles Calculations and Measurements of Thermal Diffusivity for Application to the Earth's Interior

合作研究：CSEDI——应用于地球内部的热扩散率第一原理计算和测量

• 批准号: 0757841
• 负责人: Anne Hofmeister
• 金额: $ 18.74万
• 依托单位: Washington University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2008
• 资助国家: 美国
• 起止时间: 2008-08-15 至 2014-07-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0757841&HistoricalAwards=false
• 关键词: Collaborative; Research; CSEDI; First; Principles

The Earth, like any other warm object, cools with time by shedding its heat to the surroundings. The rate limiting step is transfer of heat from inside the hotter interior to the surface, where heat release is manifest in volcanoes and motions of the crustal and lithospheric plates, which in turn generate earthquakes. These near-surface phenomena impact the biosphere and human endeavors and thus understanding the interior heat source that drives them is important. Cooling of the interior is governed by physical properties of minerals and rocks, foremost of which are thermal diffusivity and conductivity. Recent technology transfer of laser-flash analysis (LFA) from materials science now permits accurate measurement of thermal transport properties of geologic materials. However, studies of the Earth's interior require data at conditions not accessible by experiment, e.g., T 2300 K and P 100 GPa. Therefore, a robust theoretical model is needed to extrapolate the trends seen in the laboratory data to conditions in the Earth. Models are available, but have serious flaws, including being benchmarked against old data that contain significant and systematic errors. This proposal concerns development of a much improved robust theoretical model and providing accurate, state-of-the-art measurements of thermal diffusivity against which this model can be benchmarked. The proposed research is important to understand conduction in the outermost lithosphere layers and in the interior boundary between metal core and rock mantle, mantle circulations in the interior, and thermal evolution of planetary bodies due to nonlinear feedback in conservation equations. This work will further our understanding of not only planetary scale processes, but also probes the microscopic origin of heat transport.Specifically, older methods, involving physical contact with thermocouples, underestimate thermal diffusivity (D) by ~25% near 298 K, and provide incorrect signs and magnitude for D/T. Many models are based on the erroneous notion that thermal conductivity (* =*CPD, where is density and CP is heat capacity) can be obtained entirely from thermodynamic properties, which are static and depict equilibrium behavior, whereas transport by it nature is dynamic, involving interactions of vibrating atoms, and occurs under non-equilibrium conditions. We therefore propose construction of a new type of model based on a computational method that combines the quantitative, first-principles calculation of the dynamic interactions of vibrations in the mineral and microscopic Boltzmann transport theory to predict steady-state non-equilibrium distribution and changes in vibrational energy, and to benchmark this model against laser-flash measurements of simple, but relevant, systems. The mineral physics group and the solid-state theory group will work in parallel to establish reliable experimental and theoretical data, respectively. Initially, the study will focus on simple systems for which calculations are clearly feasible: Si, NaCl, and MgO, subsequently expanding to Al2O3 and Mg2SiO4. Experimental efforts will concentrate on interfacing a diamond anvil cell with the LFA to improve accuracy in measuring *

地球，像任何其他温暖的物体一样，随着时间的推移，通过向周围环境散发热量而变冷。速率限制步骤是将热量从较热的内部传递到地表，其中热量释放表现为火山以及地壳和岩石圈板块的运动，进而产生地震。这些近地表现象影响生物圈和人类活动，因此了解驱动它们的内部热源非常重要。 内部冷却受矿物和岩石的物理特性控制，其中最重要的是热扩散率和导热率。材料科学中激光闪光分析 (LFA) 的最新技术现在可以精确测量地质材料的热传输特性。 然而，对地球内部的研究需要实验无法获得的条件下的数据，例如 T 2300 K 和 P 100 GPa。 因此，需要一个强大的理论模型来将实验室数据中看到的趋势推断到地球的条件。 模型是可用的，但存在严重缺陷，包括针对包含重大系统错误的旧数据进行基准测试。该提案涉及开发一个大大改进的稳健理论模型，并提供准确、最先进的热扩散率测量结果，以此作为该模型的基准。这项研究对于理解最外层岩石圈层以及金属核和岩幔之间的内部边界的传导、内部的地幔环流以及由于守恒方程中的非线性反馈而导致的行星体的热演化具有重要意义。 这项工作不仅将进一步加深我们对行星尺度过程的理解，还将探索热传输的微观起源。具体而言，涉及与热电偶物理接触的旧方法会在 298 K 附近低估热扩散率 (D) 约 25%，并提供D/T 的符号和大小不正确。 许多模型都基于错误的观念，即热导率（* =*CPD，其中 是密度，CP 是热容）可以完全从热力学性质获得，热力学性质是静态的并描述平衡行为，而传输本质上是动态的，涉及振动原子的相互作用，并且发生在非平衡条件下。因此，我们建议构建一种基于计算方法的新型模型，该计算方法结合了矿物振动动态相互作用的定量第一原理计算和微观玻尔兹曼输运理论，以预测稳态非平衡分布和变化振动能量，并将该模型与简单但相关的系统的激光闪光测量进行基准测试。矿物物理小组和固态理论小组将并行工作，分别建立可靠的实验和理论数据。最初，该研究将重点关注计算显然可行的简单系统：Si、NaCl 和 MgO，随后扩展到 Al2O3 和 Mg2SiO4。实验工作将集中在金刚石砧座与 LFA 的连接上，以提高测量的准确性*