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

地球和任何其他温暖的物体一样，通过向周围散发热量，随着时间的推移而冷却。速度限制步骤是将热量从较热的内部转移到表面，在那里热量释放在火山以及地壳和岩石圈板块的运动中明显，这反过来又会产生地震。这些近地表现象影响了生物圈和人类的努力，因此了解驱动它们的内部热源是重要的。内部的冷却由矿物和岩石的物理性质决定，其中最重要的是热扩散性和导电性。材料科学的激光闪光分析(LFA)最近的技术转移使精确测量地质材料的热传输特性成为可能。然而，对地球内部的研究需要在实验无法获得的条件下获得数据，例如T 2300K和P 100 Gpa。因此，需要一个可靠的理论模型来推断实验室数据中看到的趋势与地球的条件。模型是可用的，但存在严重缺陷，包括以包含重大系统性错误的旧数据为基准。这项建议涉及开发一个大大改进的稳健理论模型，并提供准确的、最先进的热扩散率测量，以作为该模型的基准。这项研究对于了解岩石圈最外层和金属核与岩石地幔内部边界的传导、内部地幔环流以及由于守恒方程的非线性反馈而导致的行星体的热演化具有重要意义。这项工作不仅将加深我们对行星尺度过程的理解，而且还将探索热传输的微观起源。具体地说，旧方法涉及与热电偶的物理接触，在298K附近低估了~25%的热扩散系数(D)，并提供了错误的D/T符号和大小。许多模型基于错误的概念，即导热系数(*=*CPD，其中是密度，CP是热容)可以完全从热力学性质获得，这些热力学性质是静态的，描述了平衡行为，而热传递本质上是动态的，涉及振动原子的相互作用，发生在非平衡条件下。因此，我们建议建立一种新的模型，该模型基于一种计算方法，该方法结合了矿物和微观玻尔兹曼输运理论中振动动力学相互作用的定量第一原理计算，以预测稳态非平衡分布和振动能量的变化，并以简单但相关的系统的激光闪光测量为基准。矿物物理小组和固体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，这项研究将重点放在计算明显可行的简单体系上：硅、氯化钠和氧化镁，随后扩展到氧化铝和镁硅O4。实验工作将集中在将钻石砧座单元与LFA接口，以提高测量精度*

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 *