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Title: High-Pressure Geophysical Properties of Fcc Phase FeH X

Abstract

Face centered cubic (fcc) FeHX was synthesized at pressures of 18-68 GPa and temperatures exceeding 1,500 K. Thermally quenched samples were evaluated using synchrotron X-ray diffraction (XRD) and nuclear resonant inelastic X-ray scattering (NRIXS) to determine sample composition and sound velocities to 82 GPa. To aid in the interpretation of nonideal (X≠1) stoichiometries, two equations of state for fcc FeH X were developed, combining an empirical equation of state for iron with two distinct synthetic compression curves for interstitial hydrogen. Matching the density deficit of the Earth's core using these equations of state requires 0.8-1.1 wt % hydrogen at the core-mantle boundary and 0.2-0.3 wt % hydrogen at the interface of the inner and outer cores. Furthermore, a comparison of Preliminary Reference Earth Model (PREM) to a Birch's law extrapolation of our experimental results suggests that an iron alloy containing approximate to 0.8-1.3 wt % hydrogen could reproduce both the density and compressional velocity (V P) of the Earth's outer core.

Authors:
ORCiD logo [1]; ORCiD logo [1];  [2]; ORCiD logo [3]; ORCiD logo [3]; ORCiD logo [4]; ORCiD logo [5]; ORCiD logo [5];  [1]
  1. Univ. of Chicago, IL (United States). Dept. of the Geophysical Sciences
  2. Univ. of Illinois, Urbana, IL (United States). Dept. of Geology; Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
  3. Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
  4. Univ. of Hawaii Manoa, Honolulu, HI (United States). Hawaii Inst. of Geophysics & Planetology
  5. Univ. of Chicago, IL (United States). Center for Advanced Radiation Sources (CARS)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
National Science Foundation (NSF); National Science Foundation (NSF) - Directorate for Geosciences Division of Earth Sciences (GEO/EAR); USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1459894
Alternate Identifier(s):
OSTI ID: 1418420
Grant/Contract Number:  
AC02-06CH11357; FG02-94ER14466; EAR 11-57758; EAR 1606856; NA0001974; FG02-99ER45775
Resource Type:
Journal Article: Accepted Manuscript
Journal Name:
Geochemistry, Geophysics, Geosystems
Additional Journal Information:
Journal Volume: 19; Journal Issue: 1; Journal ID: ISSN 1525-2027
Publisher:
American Geophysical Union
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; 37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; core; hydrogen; equation of state; X-ray diffraction; nuclear resonant inelastic X-ray scattering; synchrotron Mössbauer spectroscopy

Citation Formats

Thompson, E. C., Davis, A. H., Bi, W., Zhao, J., Alp, E. E., Zhang, D., Greenberg, E., Prakapenka, V. B., and Campbell, A. J. High-Pressure Geophysical Properties of Fcc Phase FeHX. United States: N. p., 2018. Web. doi:10.1002/2017GC007168.
Thompson, E. C., Davis, A. H., Bi, W., Zhao, J., Alp, E. E., Zhang, D., Greenberg, E., Prakapenka, V. B., & Campbell, A. J. High-Pressure Geophysical Properties of Fcc Phase FeHX. United States. doi:10.1002/2017GC007168.
Thompson, E. C., Davis, A. H., Bi, W., Zhao, J., Alp, E. E., Zhang, D., Greenberg, E., Prakapenka, V. B., and Campbell, A. J. Mon . "High-Pressure Geophysical Properties of Fcc Phase FeHX". United States. doi:10.1002/2017GC007168.
@article{osti_1459894,
title = {High-Pressure Geophysical Properties of Fcc Phase FeHX},
author = {Thompson, E. C. and Davis, A. H. and Bi, W. and Zhao, J. and Alp, E. E. and Zhang, D. and Greenberg, E. and Prakapenka, V. B. and Campbell, A. J.},
abstractNote = {Face centered cubic (fcc) FeHX was synthesized at pressures of 18-68 GPa and temperatures exceeding 1,500 K. Thermally quenched samples were evaluated using synchrotron X-ray diffraction (XRD) and nuclear resonant inelastic X-ray scattering (NRIXS) to determine sample composition and sound velocities to 82 GPa. To aid in the interpretation of nonideal (X≠1) stoichiometries, two equations of state for fcc FeHX were developed, combining an empirical equation of state for iron with two distinct synthetic compression curves for interstitial hydrogen. Matching the density deficit of the Earth's core using these equations of state requires 0.8-1.1 wt % hydrogen at the core-mantle boundary and 0.2-0.3 wt % hydrogen at the interface of the inner and outer cores. Furthermore, a comparison of Preliminary Reference Earth Model (PREM) to a Birch's law extrapolation of our experimental results suggests that an iron alloy containing approximate to 0.8-1.3 wt % hydrogen could reproduce both the density and compressional velocity (VP) of the Earth's outer core.},
doi = {10.1002/2017GC007168},
journal = {Geochemistry, Geophysics, Geosystems},
number = 1,
volume = 19,
place = {United States},
year = {Mon Jan 08 00:00:00 EST 2018},
month = {Mon Jan 08 00:00:00 EST 2018}
}

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Works referenced in this record:

Finite strain isotherm and velocities for single-crystal and polycrystalline NaCl at high pressures and 300°K
journal, January 1978


Calibration of the ruby pressure gauge to 800 kbar under quasi-hydrostatic conditions
journal, January 1986

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