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Title: Experimental constraints on the sound velocities of cementite Fe 3C to core pressures

Abstract

Sound velocities of cementite Fe 3C have been measured up to 1.5 Mbar and at 300 K in a diamond anvil cell using the nuclear resonant inelastic X-ray scattering (NRIXS) technique. From the partial phonon density of states (pDOS) and equation of state (EOS) of Fe 3C, we derived its elastic parameters including shear modulus, compressional (V-p) and shear-wave (V-s) velocities to core pressures. A pressure-induced spin-pairing transition in the powdered Fe3C sample was found to occur gradually between 10 and 50 GPa by the X-ray Emission Spectroscopy (XES) measurements. Following the completion of the spin-pairing transition, the V p and V s of low-spin Fe 3C increased with pressure at a markedly lower rate than its high-spin counterpart. Our results suggest that the incorporation of carbon in solid iron to form iron carbide phases, Fe 3C and Fe 7C 3, could effectively lower the V s but respectively raise the Poisson's ratio by 0.05 and 0.07 to approach the seismically observed values for the Earth's inner core. In conclusion, the comparison with the preliminary reference Earth model (PREM) implies that an inner core composition containing iron and its carbon-rich alloys can satisfactorily explain the observed seismic properties of themore » inner core.« less

Authors:
ORCiD logo [1];  [1]; ORCiD logo [2];  [2];  [3];  [3];  [3]; ORCiD logo [3];  [4]
  1. Univ. of Hawaii at Manoa, Honolulu, HI (United States)
  2. Univ. of Michigan, Ann Arbor, MI (United States)
  3. Argonne National Lab. (ANL), Argonne, IL (United States)
  4. Carnegie Institution of Washington, Argonne, IL (United States)
Publication Date:
Research Org.:
Argonne National Lab. (ANL), Argonne, IL (United States)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22); USDOE National Nuclear Security Administration (NNSA)
OSTI Identifier:
1462754
Alternate Identifier(s):
OSTI ID: 1548200
Grant/Contract Number:  
AC02-06CH11357; FG02-94ER14466; NA0001974; AC02–06CH11357; FG02-99ER45775
Resource Type:
Accepted Manuscript
Journal Name:
Earth and Planetary Science Letters
Additional Journal Information:
Journal Volume: 494; Journal Issue: C; Journal ID: ISSN 0012-821X
Publisher:
Elsevier
Country of Publication:
United States
Language:
English
Subject:
58 GEOSCIENCES; Poisson’s ratio; compressional-wave velocity; inner core; iron carbide; magnetic transition; shear-wave velocity

Citation Formats

Chen, Bin, Lai, Xiaojing, Li, Jie, Liu, Jiachao, Zhao, Jiyong, Bi, Wenli, Alp, E. Ercan, Hu, Michael Y., and Xiao, Yuming. Experimental constraints on the sound velocities of cementite Fe3C to core pressures. United States: N. p., 2018. Web. doi:10.1016/j.epsl.2018.05.002.
Chen, Bin, Lai, Xiaojing, Li, Jie, Liu, Jiachao, Zhao, Jiyong, Bi, Wenli, Alp, E. Ercan, Hu, Michael Y., & Xiao, Yuming. Experimental constraints on the sound velocities of cementite Fe3C to core pressures. United States. doi:10.1016/j.epsl.2018.05.002.
Chen, Bin, Lai, Xiaojing, Li, Jie, Liu, Jiachao, Zhao, Jiyong, Bi, Wenli, Alp, E. Ercan, Hu, Michael Y., and Xiao, Yuming. Thu . "Experimental constraints on the sound velocities of cementite Fe3C to core pressures". United States. doi:10.1016/j.epsl.2018.05.002. https://www.osti.gov/servlets/purl/1462754.
@article{osti_1462754,
title = {Experimental constraints on the sound velocities of cementite Fe3C to core pressures},
author = {Chen, Bin and Lai, Xiaojing and Li, Jie and Liu, Jiachao and Zhao, Jiyong and Bi, Wenli and Alp, E. Ercan and Hu, Michael Y. and Xiao, Yuming},
abstractNote = {Sound velocities of cementite Fe3C have been measured up to 1.5 Mbar and at 300 K in a diamond anvil cell using the nuclear resonant inelastic X-ray scattering (NRIXS) technique. From the partial phonon density of states (pDOS) and equation of state (EOS) of Fe3C, we derived its elastic parameters including shear modulus, compressional (V-p) and shear-wave (V-s) velocities to core pressures. A pressure-induced spin-pairing transition in the powdered Fe3C sample was found to occur gradually between 10 and 50 GPa by the X-ray Emission Spectroscopy (XES) measurements. Following the completion of the spin-pairing transition, the Vp and Vs of low-spin Fe3C increased with pressure at a markedly lower rate than its high-spin counterpart. Our results suggest that the incorporation of carbon in solid iron to form iron carbide phases, Fe3C and Fe7C3, could effectively lower the Vs but respectively raise the Poisson's ratio by 0.05 and 0.07 to approach the seismically observed values for the Earth's inner core. In conclusion, the comparison with the preliminary reference Earth model (PREM) implies that an inner core composition containing iron and its carbon-rich alloys can satisfactorily explain the observed seismic properties of the inner core.},
doi = {10.1016/j.epsl.2018.05.002},
journal = {Earth and Planetary Science Letters},
number = C,
volume = 494,
place = {United States},
year = {2018},
month = {5}
}

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