期刊名称：Proceedings of the National Academy of Sciences
印刷版ISSN：0027-8424
电子版ISSN：1091-6490
出版年度：2022
卷号：119
期号：1
DOI：10.1073/pnas.2119001119
语种：English
出版社：The National Academy of Sciences of the United States of America
摘要：Significance
Earth’s liquid outer core is mainly composed of iron alloyed with ∼8 to 10% of light elements (e.g., silicon). Convection of the liquid core generates Earth’s magnetic field, which is controlled by the thermal conductivity of the core. In this study, we investigated the resistivity and thermal conductivity of iron-silicon alloys as a candidate composition in Earth’s core via high-pressure and -temperature experiments and numerical calculations. We found a near temperature independence of the resistivity in iron-silicon alloys at Earth core’s pressure and thus a high thermal conductivity. This work indicates that if silicon is the sole major light element in Earth’s core it could depress thermal convection and promote a thermally stratified layer at the topmost outer core.
Light elements in Earth’s core play a key role in driving convection and influencing geodynamics, both of which are crucial to the geodynamo. However, the thermal transport properties of iron alloys at high-pressure and -temperature conditions remain uncertain. Here we investigate the transport properties of solid hexagonal close-packed and liquid Fe-Si alloys with 4.3 and 9.0 wt % Si at high pressure and temperature using laser-heated diamond anvil cell experiments and first-principles molecular dynamics and dynamical mean field theory calculations. In contrast to the case of Fe, Si impurity scattering gradually dominates the total scattering in Fe-Si alloys with increasing Si concentration, leading to temperature independence of the resistivity and less electron–electron contribution to the conductivity in Fe-9Si. Our results show a thermal conductivity of ∼100 to 110 W⋅m
−1⋅K
−1 for liquid Fe-9Si near the topmost outer core. If Earth’s core consists of a large amount of silicon (e.g., > 4.3 wt %) with such a high thermal conductivity, a subadiabatic heat flow across the core–mantle boundary is likely, leaving a 400- to 500-km-deep thermally stratified layer below the core–mantle boundary, and challenges proposed thermal convection in Fe-Si liquid outer core.
