Optical Study of Thermal Conductivity of the Mantle Minerals at High Pressure and Temperature

高压高温下地幔矿物热导率的光学研究

• 批准号: 0711358
• 负责人: Alexander Goncharov
• 金额: $ 27万
• 依托单位: Carnegie Institution of Washington
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-09-01 至 2011-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0711358&HistoricalAwards=false
• 关键词: Optical; Study; Thermal; Conductivity; Mantle

Knowledge of thermal conductivity and thermal diffusivity of the Earth's minerals under extreme conditions is important for understanding the physical and chemical processes and their evolution in the Earth. The rate of the heat transport through the mantle is crucial for the existence and stability of the Earth's magnetic field. The temperature distribution inside the Earth's mantle depends on the rate of heat transfer by convection, conduction, and radiation. An understanding of these processes requires knowledge of the thermal conductivity as a function of pressure and temperature. In this project, the investigators propose to determine the thermal conductivity of the Earth's minerals under conditions of high pressure and temperature by direct optical measurements of its lattice and radiative contributions. The technique introduced in this proposal for measurements of the lattice thermal conductivity utilizes a periodic front surface temperature variation (measured by the spectroradiometry) of a metallic absorber surrounded by the material of interest and exposed to a pulsed laser radiation. They extract the thermal diffusivity of minerals by fitting the experimental results to the model finite element calculations. To extract the radiative part of thermal conductivity, optical properties of minerals are measured in near infrared, visible, and ultraviolet spectral ranges. The optical spectra are being measured in a wide range of pressure-temperature conditions (up to 130 GPa and 4000 K) to address the temperature effects and also the effects of the spin-pairing and perovskite- postperovskite transitions on the radiative heat transfer of the rock forming minerals in the lower mantle. Silicate perovskite and magnesiowustite, which are the two dominant phases of the Earth's lower mantle, are being studied; single crystals, grown of pre-synthesized materials with a composition close to that in the Earth's mantle, are being used as samples. The thermal conductivity of the postperovskite phase will also be measured on material synthesized by the laser heating. These experimental data give a direct estimation of the radiative and conduction parts of the thermal diffusivity, so they can be utilized in models of the thermal processes in the Earth, thus providing a crucial test of these models and our current understanding of the Earth's evolution. The results of this work have broad impact in various other fields including physics and chemistry, biology and soft matter, materials science and technology, and materials under extreme environments for advanced energy systems since all of them would benefit from the development of in situ technique for measurements of thermophysical parameters under extreme conditions. The recently designed versatile optical system for Raman, optical and IR spectroscopy is being adapted for in situ thermal conductivity measurements under extreme conditions of high pressure and temperature with external and laser heating. This is adding new features to the optical facility in Washington, DC, which is available for use by the broader high pressure research community, including visiting researchers and students, through a number of NSF-supported programs such as COMPRES and the Carnegie Summer Intern Program, as well as the DOE-supported CDAC high-pressure center headquartered at Carnegie. A range of students, including area high school students, undergraduates, graduate students, and postdoctoral associates, benefit from the scientific training at Carnegie and elsewhere through participating in cutting-edge science that is being developed throughout the course of this work.

了解地球矿物在极端条件下的导热率和热扩散率对于理解地球中的物理和化学过程及其演化非常重要。通过地幔的热传输速率对于地球磁场的存在和稳定性至关重要。地幔内部的温度分布取决于对流、传导和辐射的传热速率。要了解这些过程，需要了解热导率与压力和温度的函数关系。在该项目中，研究人员建议通过直接光学测量其晶格和辐射贡献来确定地球矿物在高压和高温条件下的导热率。本提案中引入的用于测量晶格热导率的技术利用了金属吸收体的周期性前表面温度变化（通过光谱辐射测量法测量），该金属吸收体被感兴趣的材料包围并暴露于脉冲激光辐射。 他们通过将实验结果拟合到模型有限元计算中来提取矿物的热扩散率。为了提取热导率的辐射部分，在近红外、可见光和紫外光谱范围内测量矿物的光学特性。光谱在各种压力-温度条件（高达 130 GPa 和 4000 K）下进行测量，以解决温度效应以及自旋配对和钙钛矿-后钙钛矿转变对下地幔造岩矿物辐射传热的影响。硅酸盐钙钛矿和镁方铁矿是地球下地幔的两个主要相，目前正在研究中；由预先合成的材料制成的单晶，其成分接近地幔中的成分，被用作样品。后钙钛矿相的热导率也将在激光加热合成的材料上进行测量。这些实验数据可以直接估计热扩散率的辐射和传导部分，因此可以在地球热过程模型中使用它们，从而为这些模型和我们目前对地球演化的理解提供了重要的测试。这项工作的成果对物理和化学、生物学和软物质、材料科学与技术、极端环境下先进能源系统材料等各个领域产生了广泛影响，因为所有这些领域都将受益于极端条件下热物理参数原位测量技术的发展。最近设计的用于拉曼、光学和红外光谱的多功能光学系统适用于在外部和激光加热的高压和高温极端条件下进行原位热导率测量。这为华盛顿特区的光学设施增添了新功能，该设施可供更广泛的高压研究界使用，包括访问研究人员和学生，通过许多 NSF 支持的项目，如 COMPRES 和卡内基暑期实习生项目，以及能源部支持的总部位于卡内基的 CDAC 高压中心。一系列学生，包括地区高中生、本科生、研究生和博士后，通过参与整个工作过程中正在开发的尖端科学，从卡内基和其他地方的科学培训中受益。