Title: Phase relations of Fe₃C and Fe₇C₃ up to 185 GPa and 5200 K: Implication for the stability of iron carbide in the Earth's core

Abstract

We have investigated phase relations and melting behavior of Fe₃C and Fe₇C₃ using X-ray diffraction in a laser-heated diamond cell up to 185 GPa and 5200 K. Our results show that the starting Fe₃C sample decomposes into a mixture of solid orthorhombic Fe₇C₃ and hcp-Fe at above 145 GPa upon laser heating and then transforms into Fe-C liquid and solid Fe₇C₃ at temperatures above 3400 K. Using the intensity of the diffuse scattering as a primary criteria for detecting melting, the experimentally derived liquidus for a bulk composition of Fe₃C fitted with the Simon-Glatzel equation is T_m(K) = 1800 × [1 + (P_m-5.7)/15.10 ± 2.55]^{1/2.41 ± 0.17} at 24–185 GPa, which is ~500 K higher than the melting curve of iron reported by Anzellini et al. (2013) at Earth's core pressures. The higher melting point and relative stability of Fe₇C₃ in Fe-rich Fe-C system at Earth's core conditions indicate that Fe₇C₃ could solidify out of the early Earth's molten core to become a constituent of the innermost inner core.

Authors:

Liu, Jin  ^[1];

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• Search DOE PAGES for ORCID "0000-0002-1670-8199"

Lin, Jung-Fu  ^[2];

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• Search DOE PAGES for ORCID "0000-0002-0163-5329"

Prakapenka, Vitali B.  ^[3];

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• Search DOE PAGES for ORCID "0000-0001-9270-2330"

Prescher, Clemens  ^[3];

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• Search DOE PAGES for ORCID "0000-0002-9556-1032"

Yoshino, Takashi  ^[4]

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• Search DOE PAGES for ORCID "0000-0002-5422-7396"

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1. Univ. of Texas, Austin, TX (United States). Jackson School of Geosciences, Dept. of Geological Sciences; Stanford Univ., CA (United States). Dept. of Geological Sciences
2. Univ. of Texas, Austin, TX (United States). Jackson School of Geosciences, Dept. of Geological Sciences; Center for High Pressure Science and Technology Advanced Research, Shanghai (China)
3. Univ. of Chicago, IL (United States). Consortium for Advanced Radiation Sources
4. Okayama Univ., Okayama (Japan). Inst. for Planetary Materials

Publication Date:

Wed Dec 28 00:00:00 EST 2016

Research Org.:

Univ. of Chicago, IL (United States)

Sponsoring Org.:

USDOE

OSTI Identifier:

1465341

Grant/Contract Number:  

FG02-94ER14466

Resource Type:

Accepted Manuscript

Journal Name:

Geophysical Research Letters

Additional Journal Information:

Journal Volume: 43; Journal Issue: 24; Journal ID: ISSN 0094-8276

Publisher:

American Geophysical Union

Country of Publication:

United States

Language:

English

Subject:

58 GEOSCIENCES