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Abstract Silicate liquids are important agents of thermal evolution, yet their thermal conductivity is largely unknown. Here, we determine the thermal conductivity of a silicate liquid by combining the Green‐Kubo method with a machine learning potential ofab initioquality over the entire pressure regime of the mantle. We find that the thermal conductivity of MgSiO3liquid is 1.1 W m−1 K−1at the 1 bar melting point, and 4.0 W m−1 K−1at core‐mantle boundary conditions. The thermal conductivity increases with compression, while remaining nearly constant on isochoric heating. The pressure dependence arises from the increasing bulk modulus on compression, and the weak temperature dependence arises from the saturation of the phonon mean free path due to structural disorder. The thermal conductivity of silicate liquids is less than that of ambient mantle, a contrast that may be important for understanding melt generation, and heat flux from the core.
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Non‐Isotropic Contraction and Expansion of Samples in Diamond Anvil Cells: Implications for Thermal Conductivity at the Core‐Mantle Boundary
Abstract The thermal conductivities of mantle and core materials have a major impact on planetary evolution, but their experimental determination requires precise knowledge of sample thickness at high pressure. Despite its importance, thickness in most diamond anvil cell (DAC) experiments is not measured but inferred from equations of state, assuming isotropic contraction upon compression or assuming isotropic expansion upon decompression. Here we provide evidence that in DAC experiments both assumptions are invalid for a range of mechanically diverse materials (KCl, NaCl, Ar, MgO, silica glass, Al2O3). Upon compression, these samples are ∼30–50% thinner than expected from isotropic contraction. Most surprisingly, all the studied samples continue to thin upon decompression to 10–20 GPa. Our results partially explain some discrepancies among the highly controversial thermal conductivity values of iron at Earth's core conditions. More generally, we suggest thatin situcharacterization of sample geometry is essential for conductivity measurements at high pressure.
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- Award ID(s):
- 2125954
- PAR ID:
- 10444075
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Geophysical Research Letters
- Volume:
- 49
- Issue:
- 19
- ISSN:
- 0094-8276
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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