Premium
Electrical Resistivity of Fe‐C Alloy at High Pressure: Effects of Carbon as a Light Element on the Thermal Conductivity of the Earth's Core
Author(s) -
Zhang Chengwei,
Lin JungFu,
Liu Ying,
Feng Shaomin,
Jin Changqing,
Hou Mingqiang,
Yoshino Takashi
Publication year - 2018
Publication title -
journal of geophysical research: solid earth
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.983
H-Index - 232
eISSN - 2169-9356
pISSN - 2169-9313
DOI - 10.1029/2017jb015260
Subject(s) - electrical resistivity and conductivity , materials science , van der pauw method , alloy , impurity , inner core , carbon fibers , thermal conductivity , analytical chemistry (journal) , condensed matter physics , mineralogy , metallurgy , composite material , chemistry , hall effect , physics , engineering , organic chemistry , chromatography , composite number , electrical engineering
We measured the electrical resistivity of iron, Fe 99 C 1 , Fe 3 C, and Fe 7 C 3 up to ~80 GPa using the van der Pauw method in a diamond anvil cell. The electrical resistivity of disordered Fe 99 C 1 at high pressure shows a strong impurity resistivity of carbon. The ferromagnetic‐paramagnetic transition in Fe 3 C and Fe 7 C 3 is associated with the flattening of the resistivity pressure gradient at ~6 GPa. Fe 7 C 3 exhibits the highest electrical resistivity among all iron‐light element alloys, and Fe 3 C and Fe 7 C 3 disobey the Matthiessen's rule by showing a lower electrical resistivity than a disordered iron‐carbon alloy because of chemical ordering. A comparison of the impurity resistivity between silicon, sulfur, nickel, and carbon shows that carbon has an exceedingly stronger alloying effect than other elements. If the chemical ordering observed in Fe‐Si system is held true for the Fe‐C system, the chemical ordering in Fe 7 C 3 possibly increases the thermal conductivity of the inner core and enlarges the thermal and electrical conductivity gap at the inner‐core boundary. Models of the thermal conductivity of liquid Fe 70 C 30 with 8.4 wt % carbon show a low thermal conductivity of 38 Wm −1 K −1 at the pressure‐temperature conditions of the topmost outer core. The corresponding heat flow of 6 TW at the core‐mantle boundary is notably lower than previous electrical resistivity results on Fe and Fe alloys. The alloying effect of carbon on the electrical and thermal conductivity of iron can thus play a significant role in understanding the heat flux at the core‐mantle boundary and the thermal evolution of the core.