Iron self diffusion in liquid pure iron and iron-carbon alloys

Meyer, Andreas; Hennig, L; Kargl, Florian; Unruh, Tobias

doi:10.1088/1361-648x/ab2855

Cited by 16 publications

(17 citation statements)

References 33 publications

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“…As pressure increases, it becomes challenging to accurately obtain the diffusion coefficient because the linear regime is reached at longer times relative to at low pressures. The calculated value of the Fe/Ni diffusion coefficient with a composition of Fe 72.9 Ni 7.3 C 19.8 (∼5 wt% C) is 3.15 ± 0.01 × 10 −9 m 2 /s at 0.34 GPa and 1673 K, which is closely comparable with a recent experimental measured value of 2.43 ± 0.12 × 10 −9 m 2 /s for Fe at ambient pressure and 1680 K within a composition of Fe 83.1 C 16.9 (∼4.2 wt% C) (Meyer et al, 2019), and in agreement with the experimental result ∼5 × 10 −9 m 2 /s for Fe in Fe-Si and Fe-Cr alloys at their melting temperatures (Posner et al, 2017). The diffusion coefficient of C is consistently higher than Fe/Ni, in agreement with a previous study using similar techniques (Sobolev and Mirzoev, 2013).…”

Section: Diffusion Coefficient and Shear Viscositysupporting

confidence: 90%

Short- and Intermediate-Range Structure and Dynamics of Fe-Ni-C Liquid Under Compression

et al. 2019

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Properties of liquid Fe alloys under high-pressure conditions are crucial for understanding the composition, thermal state, and dynamics of Earth's core. Experiments on such liquids, however, are often performed under pressures far below those of the outer core, necessitating long extrapolations of experimental results to core conditions. Such estimates can be complicated by light elements possibly forming pressure-dependent molecular clusters that can significantly affect the physical properties of liquids as core conditions are approached. First-principles molecular dynamics simulations were employed to compute the properties of an Fe-Ni-C liquid with a composition of Fe 3.7 Ni 0.37 C at 1673 K and pressures from 0 to 67 GPa to benchmark computational methods on pressure effects on the structure and properties of the liquid relative to low pressure experimental results. The shortrange structure is manifested by the coordination number (CN) of Fe/Ni-Fe/Ni being around 12, indicative of a nearly close-packed structure in the pressure range, and the CN of C-Fe/Ni gradual increasing from 6.5 to 8.5, indicative of an approximately octahedral to cubic transition as pressure increases. The Fe/Ni-Fe/Ni bond distance, however, is found to be 10 times more compressible than the C-Fe/Ni distance. The intermediate-range structure of Fe/Ni-Fe/Ni and C-Fe/Ni subsystems, described by a partial configurationally decomposed distribution function, undergoes substantial changes, characterized by a significant increase of the number of polyhedra that share 3 atoms with each other. Such dense configurations are related to an increased bulk modulus, decreased diffusion coefficient, decreased activation volume for diffusion, and increased shear viscosity. Reproducing the experimental observations at low pressures provides important support for modeling the liquid under the conditions relevant to the outer core.

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Section: Diffusion Coefficient and Shear Viscositysupporting

confidence: 90%

Short- and Intermediate-Range Structure and Dynamics of Fe-Ni-C Liquid Under Compression

et al. 2019

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“…Here, we assume that core material infiltrates the mantle. Therefore, in the influx scenario we follow assumptions of Hayden and Watson (2007), Otsuka and Karato (2012), Bouffard et al (2019), andMeyer et al (2019) where the chemical diffusivity could be in the range of 𝐴𝐴 10 −9 𝑚𝑚 2 𝑠𝑠 (amounting to a Lewis number of only 10 3 ) for iron or HSE. The comparison of the results from the influx scenario to those of the primordial layer scenario (with no basal influx) shows that both scenarios give a qualitatively similar behavior.…”

Section: Discussionmentioning

confidence: 99%

Formation of Thermochemical Heterogeneities by Core‐Mantle Interaction

Stein

Hansen

2023

JGR Solid Earth

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“…denotes experimental data at the ambient melting point (7.019 g/cm 3 , 1811 K). 12.0 53 0.83 46 2.36 48 0.28 47 5.44 49 a 2pt-mf.…”

Section: The Journal Of Chemical Physicsmentioning

confidence: 99%

Atomic transport properties of liquid iron at conditions of planetary cores

Sun

Zhang

et al. 2021

The Journal of Chemical Physics

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Atomic transport properties of liquid iron are important for understanding the core dynamics and magnetic field generation of terrestrial planets. Depending on the sizes of planets and their thermal histories, planetary cores may be subject to quite different pressures (P) and temperatures (T). However, previous studies on the topic mainly focus on the P-T range associated with the Earth's outer core; a systematic study covering conditions from small planets to massive exoplanets is lacking. Here, we calculate the self-diffusion coefficient (D) and viscosity (η) of liquid iron via ab initio molecular dynamics from 7.0 to 25 g/cm 3 and 1800 to 25 000 K. We find that D and η are intimately related and can be fitted together using a generalized free volume model. The resulting expressions are simpler than those from previous studies where D and η were treated separately. Moreover, the new expressions are in accordance with the quasi-universal atomic excess entropy (Sex) scaling law for strongly coupled liquids, with normalized diffusivity D ⋆ = 0.621 exp(0.842Sex) and viscosity η ⋆ = 0.171 exp(−0.843Sex). We determine D and η along two thermal profiles of great geophysical importance: the iron melting curve and the isentropic line anchored at the ambient melting point. The variations of D and η along these thermal profiles can be explained by the atomic excess entropy scaling law, demonstrating the dynamic invariance of the system under uniform time and space rescaling. Accordingly, scale invariance may serve as an underlying mechanism to unify planetary dynamos of different sizes.

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Iron self diffusion in liquid pure iron and iron-carbon alloys

Cited by 16 publications

References 33 publications

Short- and Intermediate-Range Structure and Dynamics of Fe-Ni-C Liquid Under Compression

Short- and Intermediate-Range Structure and Dynamics of Fe-Ni-C Liquid Under Compression

Formation of Thermochemical Heterogeneities by Core‐Mantle Interaction

Atomic transport properties of liquid iron at conditions of planetary cores

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