High Pressure-Temperature Equations of State, Oxygen Fugacity, and Earth's Core

材料在高压和高温下的性质对于了解地球内部深处是必不可少的。该项目通过现场测量高压、高温条件下的晶胞体积(高达100 Gpa和2500K)，扩展了我们对几种地球物理重要材料的状态方程(压力-体积-温度关系)的理解。同时测量金属及其共存氧化物的压力-体积-温度比单独测量每个相提供了更精确的相对状态方程的测量。同步辐射X射线衍射法用于测量这两种相的体积，高压和高温是使用激光加热的金刚石顶压室产生的。使用多锤头压力机的补充研究也在进行中；这些研究加强了较低压力范围(25 Gpa)的数据集。这两组实验的实验方法在早期的调查中都得到了成功的证明，但并未得到广泛应用。正在对金属和氧化物进行初步研究，包括铁-铁氧化物、镍-镍氧化物和Re-Re氧化物。这些数据在地球内部的研究中有几个应用。其一是改进了氧逸度缓冲器，通过积分精确的、实验确定的共存金属氧化物相的相对体积，将其扩展到高压。这些结果使人们能够更好地量化高压下的氧势，这是理解例如核-地幔相互作用和地幔中元素分配所必需的。此外，许多高压地球化学研究的氧逸度条件要么受这些金属氧化物缓冲液的控制，要么参考这些缓冲液。精确比较基于不同缓冲液的实验结果需要了解这些缓冲液随着压力的增加而发生的相对位移。最后，这些研究有助于将实验确定的候选核心成分的密度与观测到的、受地震约束的核心密度剖面进行直接比较。这里需要更多的数据来提高精度和减少外推，特别是在高温情况下。从这个项目中获得的信息将有助于我们了解行星的化学演化和核心的形成。

The properties of materials at high pressure and temperature are essential for understanding the Earth's deep interior. This project is extending our understanding of the equations of state (pressure - volume - temperature relationships) of several geophysically important materials, through in situ measurement of unit cell volumes under high pressure, high temperature conditions (up to 100 GPa and 2500 K). Simultaneous pressure - volume - temperature measurements of a metal and its coexisting oxide provide a more precise measure of their relative equations of state than measurements of each phase separately. Synchrotron x-ray diffraction is used to measure volumes of both phases, and high pressures and temperatures are generated using a laser heated diamond anvil cell. Complementary studies using a multi-anvil press are also underway; these strengthen the data set in the lower pressure range ( 25 GPa). The experimental methodologies for both sets of experiments was successfully demonstrated in earlier investigations, but had not been broadly applied. Metals and oxides are being studied primarily, including iron-iron oxide, nickel-nickel oxide, and rhenium-rhenium oxide. There are several applications of these data to studies of the Earth's interior. One is the improved extension of oxygen fugacity buffers to high pressures, by integration of precise, experimentally determined relative volumes of coexisting metal-oxide phases. These results allow one to better quantify the oxygen potential at high pressures, which is needed to understand, for example, core-mantle interaction and elemental partitioning in the mantle. Furthermore, the oxygen fugacity conditions of many high pressure geochemical studies are either controlled by, or referenced to, these metal-oxide buffers. Precise comparison of experimental results that are based on different buffers requires knowledge of the relative shifts of those buffers with increasing pressure. Finally, these studies facilitate direct comparison of experimentally determined densities of candidate core constituents with the observed, seismologically constrained density profiles of the core. More data have been needed here to improve precision and reduce extrapolations, especially at high temperature. The information gained from this project will benefit our understanding of the chemical evolution of the planet and the formation of the core.