TY - JOUR
T1 - Electrical Resistivity of Fe-C Alloy at High Pressure
T2 - Effects of Carbon as a Light Element on the Thermal Conductivity of the Earth's Core
AU - Zhang, Chengwei
AU - Lin, Jung Fu
AU - Liu, Ying
AU - Feng, Shaomin
AU - Jin, Changqing
AU - Hou, Mingqiang
AU - Yoshino, Takashi
N1 - Funding Information:
We acknowledge Youjun Zhang for his constructive suggestions. We appreci ate technical assistance from Yanping Yang in the FIB analysis of the quenched samples. We thank Rusty Roberts and Freyja O’Toole for their edits and comments on this paper. We also thank anonymous reviewers for their comments and suggestions and editor M. Walter for his constructive comments. J.F.L. acknowledges support from the Geophysics and CSEDI Programs of the National Science Foundation (NSF), Deep Carbon Observatory of the Sloan Foundation, and Center for High Pressure Science and Advanced Technology (HPSTAR). The data for this paper are available in supplements.
Publisher Copyright:
©2018. American Geophysical Union. All Rights Reserved.
PY - 2018/5
Y1 - 2018/5
N2 - We measured the electrical resistivity of iron, Fe99C1, Fe3C, and Fe7C3 up to ~80 GPa using the van der Pauw method in a diamond anvil cell. The electrical resistivity of disordered Fe99C1 at high pressure shows a strong impurity resistivity of carbon. The ferromagnetic-paramagnetic transition in Fe3C and Fe7C3 is associated with the flattening of the resistivity pressure gradient at ~6 GPa. Fe7C3 exhibits the highest electrical resistivity among all iron-light element alloys, and Fe3C and Fe7C3 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 Fe7C3 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 Fe70C30 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.
AB - We measured the electrical resistivity of iron, Fe99C1, Fe3C, and Fe7C3 up to ~80 GPa using the van der Pauw method in a diamond anvil cell. The electrical resistivity of disordered Fe99C1 at high pressure shows a strong impurity resistivity of carbon. The ferromagnetic-paramagnetic transition in Fe3C and Fe7C3 is associated with the flattening of the resistivity pressure gradient at ~6 GPa. Fe7C3 exhibits the highest electrical resistivity among all iron-light element alloys, and Fe3C and Fe7C3 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 Fe7C3 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 Fe70C30 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.
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U2 - 10.1029/2017JB015260
DO - 10.1029/2017JB015260
M3 - Article
AN - SCOPUS:85047608516
VL - 123
SP - 3564
EP - 3577
JO - Journal of Geophysical Research
JF - Journal of Geophysical Research
SN - 0148-0227
IS - 5
ER -