Hydrogen and Silicon Effects on Hexagonal Close Packed Fe Alloys at High Pressures: Implications for the Composition of Earth's Inner Core

Fu, Suyu; Chariton, Stella; Prakapenka, Vitali B.; Shim, Sang‐Heon

doi:10.1029/2022jb026016

Hydrogen and Silicon Effects on Hexagonal Close Packed Fe Alloys at High Pressures: Implications for the Composition of Earth's Inner Core

Journal Article · Fri Apr 14 00:00:00 EDT 2023 · Journal of Geophysical Research. Solid Earth

DOI:https://doi.org/10.1029/2022jb026016· OSTI ID:2423461

^[1]; Chariton, Stella ^[2]; ^[2]; ^[3]

Arizona State Univ., Tempe, AZ (United States); Univ. of Tokyo (Japan)
Univ. of Chicago, IL (United States)
Arizona State Univ., Tempe, AZ (United States)

Hexagonal close-packed (hcp) structured Fe-Ni alloy is believed to be the dominant phase in the Earth's inner core. This phase is expected to contain 4%–5% light elements, such as Si and H. While the effects of individual light element candidates on the equation of state (EoS) of the hcp Fe metal have been studied, their combined effects remain largely unexplored. Here, in this study, we report the equations of state for two hcp-structured Fe-Si-H alloys, namely Fe_0.83Si_0.17H_0.07 and Fe_0.83Si_0.17H_0.46, using synchrotron X-ray diffraction measurements up to 125 GPa at 300 K. These alloys were synthesized by cold compression of Fe-9wt%Si in either pure H₂ or Ar-H₂ mixture medium in diamond-anvil cells. The volume increase caused by a H atom in hcp Fe-Si-H alloys is approximately eight times greater than that by a Si atom. We used the improved data set to develop a composition-dependent EoS that covers a wide range of compositions. Our calculated density and bulk sound velocity of hcp Fe-Si-H alloys suggest a large trade-off between Si and H contents in fitting the seismic properties of the inner core. Combining our new EoS with geophysical and geochemical constraints, we propose 1.6–3 wt% Si and 0.15–0.6 wt% H in the Earth's inner core.

View Accepted Manuscript (DOE)

Research Organization:: Argonne National Laboratory (ANL), Argonne, IL (United States). Advanced Photon Source (APS)

Sponsoring Organization:: National Science Foundation (NSF); USDOE Office of Science (SC), Basic Energy Sciences (BES). Scientific User Facilities (SUF)

Grant/Contract Number:: AC02-06CH11357

OSTI ID:: 2423461

Journal Information:: Journal of Geophysical Research. Solid Earth, Journal Name: Journal of Geophysical Research. Solid Earth Journal Issue: 4 Vol. 128; ISSN 2169-9356; ISSN 2169-9313

Publisher:: American Geophysical UnionCopyright Statement

Country of Publication:: United States

Language:: English

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