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Open AccessArticle

Thermal Equation of State of Fe3C to 327 GPa and Carbon in the Core

1
Department of Earth Science, Graduate School of Science, Tohoku University, 6-3 Aza-Aoba, Aramaki, Aoba-ku, Sendai 980-8571, Japan
2
Japan Synchrotron Radiation Research Institute, 1-1-1 Kouto, Sayo 679-5198, Japan
*
Author to whom correspondence should be addressed.
Minerals 2019, 9(12), 744; https://doi.org/10.3390/min9120744
Received: 16 October 2019 / Revised: 25 November 2019 / Accepted: 26 November 2019 / Published: 30 November 2019
(This article belongs to the Special Issue Mineral Physics—In Memory of Orson Anderson)
The density and sound velocity structure of the Earth’s interior is modeled on seismological observations and is known as the preliminary reference Earth model (PREM). The density of the core is lower than that of pure Fe, which suggests that the Earth’s core contains light elements. Carbon is one plausible light element that may exist in the core. We determined the equation of state (EOS) of Fe3C based on in situ high-pressure and high-temperature X-ray diffraction experiments using a diamond anvil cell. We obtained the PV data of Fe3C up to 327 GPa at 300 K and 70–180 GPa up to around 2300 K. The EOS of nonmagnetic (NM) Fe3C was expressed by two models using two different pressure scales and the third-order Birch–Murnaghan EOS at 300 K with the Mie–Grüneisen–Debye EOS under high-temperature conditions. The EOS can be expressed with parameters of V0 = 148.8(±1.0) Å3, K0 = 311.1(±17.1) GPa, K0 = 3.40(±0.1), γ0 = 1.06(±0.42), and q = 1.92(±1.73), with a fixed value of θ0 = 314 K using the KBr pressure scale (Model 1), and V0 = 147.3(±1.0) Å3, K0 = 323.0(±16.6) GPa, K0 = 3.43(±0.09), γ0 = 1.37(±0.33), and q = 0.98(±1.01), with a fixed value of θ0 = 314 K using the MgO pressure scale (Model 2). The density of Fe3C under inner core conditions (assuming P = 329 GPa and T = 5000 K) calculated from the EOS is compatible with the PREM inner core. View Full-Text
Keywords: iron carbide; Fe3C; equation of state; high-pressure and high-temperature; inner core; in situ X-ray diffraction iron carbide; Fe3C; equation of state; high-pressure and high-temperature; inner core; in situ X-ray diffraction
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Takahashi, S.; Ohtani, E.; Ikuta, D.; Kamada, S.; Sakamaki, T.; Hirao, N.; Ohishi, Y. Thermal Equation of State of Fe3C to 327 GPa and Carbon in the Core. Minerals 2019, 9, 744.

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