Structures and Densities of Silicate Liquids Under High Pressure

知识价值。该提案要求资金支持(1)高压下硅酸盐液体结构的实验研究，(2)使用新的同步加速器x射线衍射和吸收方法研究硅酸盐和岩浆液体的压力-体积-温度（P-V-T）关系。x射线散射技术将用于确定金刚石砧胞（DAC）中液体物质在大范围压力下直至地核地幔边界的结构。一种新开发的x射线吸收方法将用于测量高压-高温条件下硅酸盐液体的密度。为了达到熔融难熔硅酸盐所需的高温，将双面激光加热DAC技术和最近开发的内部加热DAC技术与同步加速器x射线束结合使用来分析液体结构。外部加热DAC和巴黎-爱丁堡电池将用于液体密度测量。这些实验将提供在高压和高温下的硅酸盐玻璃、锗酸盐和硅酸盐液体以及岩浆液体的结构和密度。将特别努力研究压力增加的液体的局部结构变化，包括配位数的变化。四面体液体和八面体液体的压缩行为将在它们的稳定场中被确定。这些结果将为液晶密度反演提供重要数据，并为行星历史上似是而非的岩浆海洋的分化和动力学模型设定约束条件。拟议的研究还将为了解在地球上地幔和下地幔底部的低速带和超低速带中可能存在的熔体提供实验证据。更广泛的影响。本提案支持一名博士后，该博士后将在开展研究活动中发挥重要作用。本次提案的PI是一名光束科学家，有机会与来自世界各地的大量研究生，博士后科学家和资深科学家一起工作。从提出的具有挑战性的实验中获得的经验和技术解决方案对外部用户执行自己的实验很有用。拟议的研究结果将在各种会议上报告，并在科学期刊上发表。

Intellectual Merit. This proposal requests funds to support experimental studies of (1) structures of silicate liquids at high pressures, and (2) the pressure-volume-temperature (P-V-T) relations of silicate and magmatic liquids using new synchrotron x-ray diffraction and absorption methods. An x-ray scattering technique will be utilized to determine structures of liquid materials in diamond anvil cells (DAC) under a wide range of pressures up to the core mantle boundary. A newly developed x-ray absorption method will be used to measure densities of silicate liquids at high pressure-temperature conditions. To reach the required high temperatures for melting refractory silicates, a double sided laser heated DAC technique and a recently developed internally heated DAC technique are used in combination with synchrotron x-ray beams to analyze the liquid structures. An externally heated DAC and the Paris-Edinburgh cell will be used for liquid density measurements. These experiments will provide structures and densities of silicate glasses, germanate and silicate liquids, and magmatic liquids at high pressures and high temperatures. Particular effort will be put on the local structural change, including the change in coordination number, in liquids with increasing pressures. The compression behavior of both tetrahedral liquids and octahedral liquids will be determined in their stability fields. These results will provide crucial data on liquid-crystal density inversions and set constraints on differentiation and dynamic models in plausible magma oceans in planetary history. The proposed research will also provide experimental evidence for understanding the possible presence of melts in the low and ultra-low velocity zones at the bottom regions of the Earth's upper mantle and the lower mantle.Broader Impacts. This proposal supports a post-doctoral associate who will play a major role in carrying out the research activities. The PI of this proposal is a beamline scientist, with the opportunity of working with a large number of graduate students, post-doctoral scientists, and senior scientists from all over the world. The experience and technical solutions from the proposed challenging experiments are useful for outside users in performing their own. The results of the proposed research will be reported in various meetings and published in scientific journals.