Equation of State Measurements on Iron Near the Melting Curve at Planetary Core Conditions by Shock and Ramp Compressions
Equation of State Measurements on Iron Near the Melting Curve at Planetary Core Conditions by Shock and Ramp Compressions
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DOI：
10.1029/2020jb020008
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发表时间：
2021-02
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通讯作者：
S. Grant;Tommy Ao;C. Seagle;A. Porwitzky;J. Davis;Kyle R. Cochrane;Daniel H. Dolan;Jung-Fu Lin;T. Ditmire;Aaron C. Bernstein
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作者：
S. Grant;Tommy Ao;C. Seagle;A. Porwitzky;J. Davis;Kyle R. Cochrane;Daniel H. Dolan;Jung-Fu Lin;T. Ditmire;Aaron C. Bernstein
地球的外核主要由液态铁组成，内核边界由熔线与地温的交点决定。虽然对固态铁的热力学状态方程有很多研究，但液态铁的状态方程相对尚未被探索。我们利用桑迪亚国家实验室 Z 机的冲击斜坡功能，使用动态压缩来诊断铁的高压液体状态方程。该技术通过最初冲击样品并随后驱动进一步的无冲击压缩来测量 Hugoniot 上的材料状态。行星研究极大地受益于等熵、非于贡尼奥实验，因为它们可以涵盖接近行星内部绝热剖面的压力-温度（P-T）条件。我们使用这种方法将铁驱动到类似于地球外核边界的 P-T 条件，沿着液体中的高温等熵从 275 GPa 到 400 GPa。我们使用粒子速度迹线的混合后向积分-前向拉格朗日技术推导了状态方程，以确定样品的压力-密度历史。我们的结果与之前发布的状态方程表 SESAME 92141 非常一致。利用我们的数据和之前关于液态铁的实验数据，我们提供了有关铁熔线的新信息，并为基于 Vinet 的状态方程导出了新参数。该表和我们的参数化状态方程用于提供对系外行星内部液态铁芯的压力、质量和密度进行建模的更新方法。
The outer core of the Earth is composed primarily of liquid iron, and the inner core boundary is governed by the intersection of the melt line and the geotherm. While there are many studies on the thermodynamic equation of state for solid iron, the equation of state of liquid iron is relatively unexplored. We use dynamic compression to diagnose the high‐pressure liquid equation of state of iron by utilizing the shock‐ramp capability at Sandia National Laboratories’ Z‐Machine. This technique enables measurements of material states off the Hugoniot by initially shocking samples and subsequently driving a further, shockless compression. Planetary studies benefit greatly from isentropic, off‐Hugoniot experiments since they can cover pressure‐temperature (P‐T) conditions that are close to adiabatic profiles found in planetary interiors. We used this method to drive iron to P‐T conditions similar to those of the Earth’s outer‐inner core boundary, along an elevated‐temperature isentrope in the liquid from 275 GPa to 400 GPa. We derive the equation of state using a hybrid backward integration – forward Lagrangian technique on particle velocity traces to determine the pressure‐density history of the sample. Our results are in excellent agreement with SESAME 92141, a previously published equation of state table. With our data and previous experimental data on liquid iron we provide new information on the iron melting line and derive new parameters for a Vinet‐based equation of state. The table and our parameterized equation of state are applied to provide an updated means of modeling the pressure, mass, and density of liquid iron cores in exoplanetary interiors.