Equation of State Measurements on Iron Near the Melting Curve at Planetary Core Conditions by Shock and Ramp Compressions
Abstract
Abstract 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 datamore »
- Authors:
-
- Univ. of Texas, Austin, TX (United States); Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
- Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
- Univ. of Texas, Austin, TX (United States)
- Publication Date:
- Research Org.:
- Sandia National Lab. (SNL-NM), Albuquerque, NM (United States)
- Sponsoring Org.:
- USDOE National Nuclear Security Administration (NNSA); National Science Foundation (NSF)
- OSTI Identifier:
- 1772022
- Alternate Identifier(s):
- OSTI ID: 1786807
- Report Number(s):
- SAND-2021-2739J
Journal ID: ISSN 2169-9313; 694630
- Grant/Contract Number:
- AC04-94AL85000; NA0003525
- Resource Type:
- Accepted Manuscript
- Journal Name:
- Journal of Geophysical Research. Solid Earth
- Additional Journal Information:
- Journal Volume: 126; Journal Issue: 3; Journal ID: ISSN 2169-9313
- Publisher:
- American Geophysical Union
- Country of Publication:
- United States
- Language:
- English
- Subject:
- 58 GEOSCIENCES; equation of state; iron; planets
Citation Formats
Grant, Sean Campbell, Ao, Tommy, Seagle, Christopher T., Porwitzky, Andrew James, Davis, Jean-Paul, Cochrane, Kyle R., Dolan, Daniel H., Lin, Jung-Fu, Ditmire, Todd, and Bernstein, Aaron C. Equation of State Measurements on Iron Near the Melting Curve at Planetary Core Conditions by Shock and Ramp Compressions. United States: N. p., 2021.
Web. doi:10.1029/2020jb020008.
Grant, Sean Campbell, Ao, Tommy, Seagle, Christopher T., Porwitzky, Andrew James, Davis, Jean-Paul, Cochrane, Kyle R., Dolan, Daniel H., Lin, Jung-Fu, Ditmire, Todd, & Bernstein, Aaron C. Equation of State Measurements on Iron Near the Melting Curve at Planetary Core Conditions by Shock and Ramp Compressions. United States. https://doi.org/10.1029/2020jb020008
Grant, Sean Campbell, Ao, Tommy, Seagle, Christopher T., Porwitzky, Andrew James, Davis, Jean-Paul, Cochrane, Kyle R., Dolan, Daniel H., Lin, Jung-Fu, Ditmire, Todd, and Bernstein, Aaron C. Sun .
"Equation of State Measurements on Iron Near the Melting Curve at Planetary Core Conditions by Shock and Ramp Compressions". United States. https://doi.org/10.1029/2020jb020008. https://www.osti.gov/servlets/purl/1772022.
@article{osti_1772022,
title = {Equation of State Measurements on Iron Near the Melting Curve at Planetary Core Conditions by Shock and Ramp Compressions},
author = {Grant, Sean Campbell and Ao, Tommy and Seagle, Christopher T. and Porwitzky, Andrew James and Davis, Jean-Paul and Cochrane, Kyle R. and Dolan, Daniel H. and Lin, Jung-Fu and Ditmire, Todd and Bernstein, Aaron C.},
abstractNote = {Abstract 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.},
doi = {10.1029/2020jb020008},
journal = {Journal of Geophysical Research. Solid Earth},
number = 3,
volume = 126,
place = {United States},
year = {Sun Feb 07 00:00:00 EST 2021},
month = {Sun Feb 07 00:00:00 EST 2021}
}
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