Ab initio studies of the short-range atomic structure of liquid iron–carbon alloys

Sobolev, Andrey; Мирзоев, А. А.

doi:10.1016/j.molliq.2012.11.019

Cited by 14 publications

(8 citation statements)

References 30 publications

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“…These data indicate that the basic local structure of the liquid Fe‐C alloy is essentially same as that of liquid Fe. These results are consistent with ambient‐pressure structural studies (Boronenkov et al, ; Sobolev & Mirzoev, ).…”

Section: Resultssupporting

confidence: 92%

Effect of Silicon, Carbon, and Sulfur on Structure of Liquid Iron and Implications for Structure‐Property Relations in Liquid Iron‐Light Element Alloys

Shibazaki

Kono

2018

JGR Solid Earth

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Planetary cores are considered to be composed of iron (Fe) and light elements. Extensive studies on structure and properties of crystalline Fe‐light element alloys have been carried out to discuss composition and structure of the solid inner core. In contrast, structure and properties of liquid Fe‐light element alloys, which are important to discuss nature and dynamics of the liquid outer core, remain poorly understood. Here we conducted series of liquid structure measurements to systematically understand effect of silicon (Si), carbon (C), and sulfur (S) on structure of liquid Fe. We found that incorporation of Si in liquid Fe shortens the nearest (r1) and second (r2) neighbor distances, while incorporation of C and small amount of S expands these distances. The different structural behavior is interpreted in view of different light‐element incorporation mechanisms: substitutional incorporation of Si and interstitial incorporation of C and S. All light elements lower density of liquid Fe regardless of shortening or expansion of the r1 and r2 distances, while P‐wave velocities of liquid Fe‐light element alloys show linear increase with shortening of the r1 and r2. The different light‐element incorporation behavior in the structure of liquid Fe and the resultant variation in the properties of liquid Fe‐light element alloys should be important in understanding behavior of liquid Fe‐light element alloys in the planetary cores.

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Section: Resultssupporting

confidence: 92%

Effect of Silicon, Carbon, and Sulfur on Structure of Liquid Iron and Implications for Structure‐Property Relations in Liquid Iron‐Light Element Alloys

Shibazaki

Kono

2018

JGR Solid Earth

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“…Our experimental PDFs of FeNi5C and FeNi3C liquids also show a weak but visible peak at ~1.8–1.9 Å at each pressure of the measurements (Figures and S3). As suggested by our MD simulations and previous MD results (Sobolev & Mirzoev, ), this peak is associated with the Fe‐C pairs. The calculated PDFs from MD simulations yield no peak or zero intensity for r < 1.6 Å.…”

Section: Resultssupporting

confidence: 87%

“…The calculated total CNs for the Fe/Ni‐Fe/Ni coordination have an initial increase from 11.8 to 12.2 across the liquid structural transition but remain almost constant at 12.2 at 5–67 GPa. A previous study suggested that regions with Fe 3 C‐like structure (a deformed epsilon( ε )‐Fe lattice) exist in the Fe‐C liquids when the carbon concentration is higher than 3 wt % at ambient condition (Sobolev & Mirzoev, ). As revealed by our MD calculations, the C‐Fe/Ni polyhedra are also found in the liquid structure and they become severely distorted as compared to crystal Fe 3 C structure at high pressure (Figure S4).…”

Section: Resultsmentioning

confidence: 99%

Polyamorphic Transformations in Fe‐Ni‐C Liquids: Implications for Chemical Evolution of Terrestrial Planets

et al. 2017

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During the formation of the Earth's core, the segregation of metallic liquids from silicate mantle should have left behind evident geochemical imprints on both the mantle and the core. Some distinctive geochemical signatures of the mantle‐derived rocks likely own their origin to the metal‐silicate differentiation of the primitive Earth, setting our planet apart from undifferentiated meteorites as well as terrestrial planets or moons isotopically and compositionally. Understanding the chemical evolution of terrestrial planetary bodies requires knowledge on properties of both liquid iron alloys and silicates equilibrating under physicochemical conditions pertinent to the deep magma ocean. Here we report experimental and computational results on the pressure‐induced structural evolution of iron‐nickel liquids alloyed with carbon. Our X‐ray diffraction experiments up to 7.3 gigapascals (GPa) demonstrate that Fe‐Ni (Fe90Ni10) liquids alloyed with 3 and 5 wt % carbon undergo a polyamorphic liquid structure transition at approximately 5 GPa. Corroborating the experimental observations, our first‐principles molecular dynamic calculations reveal that the structural transitions result from the marked prevalence of three‐atom face‐sharing polyhedral connections in the liquids at >5 GPa. The structure and polyamorphic transitions of liquid iron‐nickel‐carbon alloys govern their physical and chemical properties and may thus cast fresh light on the chemical evolution of terrestrial planets and moons.

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“…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). The ratio of the diffusion coefficients, D C /D Fe/Ni , is ∼1.7 at pressures less than ∼5 GPa, and ∼2.4 at pressures greater than ∼5 GPa.…”

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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Ab initio studies of the short-range atomic structure of liquid iron–carbon alloys

Cited by 14 publications

References 30 publications

Effect of Silicon, Carbon, and Sulfur on Structure of Liquid Iron and Implications for Structure‐Property Relations in Liquid Iron‐Light Element Alloys

Effect of Silicon, Carbon, and Sulfur on Structure of Liquid Iron and Implications for Structure‐Property Relations in Liquid Iron‐Light Element Alloys

Polyamorphic Transformations in Fe‐Ni‐C Liquids: Implications for Chemical Evolution of Terrestrial Planets

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

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