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Phase relations of Fe 3 C and Fe 7 C 3 up to 185 GPa and 5200 K: Implication for the stability of iron carbide in the Earth's core
Author(s) -
Liu Jin,
Lin JungFu,
Prakapenka Vitali B.,
Prescher Clemens,
Yoshino Takashi
Publication year - 2016
Publication title -
geophysical research letters
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.007
H-Index - 273
eISSN - 1944-8007
pISSN - 0094-8276
DOI - 10.1002/2016gl071353
Subject(s) - liquidus , materials science , analytical chemistry (journal) , orthorhombic crystal system , melting point , diamond anvil cell , carbide , phase (matter) , inner core , earth (classical element) , diffraction , outer core , crystallography , crystal structure , chemistry , metallurgy , alloy , physics , optics , organic chemistry , chromatography , composite material , mathematical physics
We have investigated phase relations and melting behavior of Fe 3 C and Fe 7 C 3 using X‐ray diffraction in a laser‐heated diamond cell up to 185 GPa and 5200 K. Our results show that the starting Fe 3 C sample decomposes into a mixture of solid orthorhombic Fe 7 C 3 and hcp‐Fe at above 145 GPa upon laser heating and then transforms into Fe‐C liquid and solid Fe 7 C 3 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 Fe 3 C 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 Fe 7 C 3 in Fe‐rich Fe‐C system at Earth's core conditions indicate that Fe 7 C 3 could solidify out of the early Earth's molten core to become a constituent of the innermost inner core.