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

Jin Liu, Jung Fu Lin, Vitali B. Prakapenka, Clemens Prescher, Takashi Yoshino

Research output: Contribution to journalArticle

19 Citations (Scopus)

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 Tm(K) = 1800 × [1 + (Pm − 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.

Original languageEnglish
Pages (from-to)12,415-12,422
JournalGeophysical Research Letters
Volume43
Issue number24
DOIs
Publication statusPublished - Dec 28 2016

Keywords

  • Earth's core
  • iron carbide
  • melting
  • X-ray diffraction

ASJC Scopus subject areas

  • Geophysics
  • Earth and Planetary Sciences(all)

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