Thermal expansion of iron-rich alloys and implications for the Earth's core

Chen, Bin; Gao, Lili; Funakoshi, K.; Li, Jie

doi:10.1073/pnas.0610474104

Cited by 41 publications

(47 citation statements)

References 44 publications

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“…The density deficit of hcp-Fe 0.85 Si 0.15 is fairly independent of the density increase, though Fe 3 C, Fe 3 S, and FeH systems seem to show a marginally positive slope (33,37,39), whereas FeO displays a negative slope (33). We have also calculated the density deficits of Fe alloys using the V Φ − ρ profiles from the XRD measurements following the same method to derive the density deficits from the V P − ρ profiles (29,30,35,(50)(51)(52)(53)(54)(55)(56)(57)(58) (Fig. 4B).…”

Section: Resultsmentioning

confidence: 99%

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Sound velocities of Fe and Fe-Si alloy in the Earth’s core

Mao

Lin

Liu

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

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101

138

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Compressional wave velocity-density (V P − ρ) relations of candidate Fe alloys at relevant pressure-temperature conditions of the Earth's core are critically needed to evaluate the composition, seismic signatures, and geodynamics of the planet's remotest region. Specifically, comparison between seismic V P − ρ profiles of the core and candidate Fe alloys provides first-order information on the amount and type of potential light elements-including H, C, O, Si, and/or S-needed to compensate the density deficit of the core. To address this issue, here we have surveyed and analyzed the literature results in conjunction with newly measured V P − ρ results of hexagonal closest-packed (hcp) Fe and hcp-Fe 0.85 Si 0.15 alloy using in situ highenergy resolution inelastic X-ray scattering and X-ray diffraction. The nature of the Fe-Si alloy where Si is readily soluble in Fe represents an ideal solid-solution case to better understand the lightelement alloying effects. Our results show that high temperature significantly decreases the V P of hcp-Fe at high pressures, and the Fe-Si alloy exhibits similar high-pressure V P − ρ behavior to hcp-Fe via a constant density offset. These V P − ρ data at a given temperature can be better described by an empirical power-law function with a concave behavior at higher densities than with a linear approximation. Our new datasets, together with literature results, allow us to build new V P − ρ models of Fe alloys in order to determine the chemical composition of the core. Our models show that the V P − ρ profile of Fe with 8 wt % Si at 6,000 K matches well with the Preliminary Reference Earth Model of the inner core.compressional-wave velocity | high pressure-temperature E nigmatic properties of the Earth's inner core have recently been discovered including differential super-rotation (1), seismic anisotropies (2-4), and fine-scale seismic heterogeneities (5, 6). Deciphering these observations requires solid knowledge about the composition of the Earth's inner core and, therefore, the elasticity of candidate Fe alloys (7-16). Since F. Birch pointed out in the 1950s that Earth's core is too dense if composed of Fe or Fe-Ni alloy alone (13), a number of candidate major light elements, including oxygen (O), silicon (Si), sulfur (S), carbon (C), and hydrogen (H), have been suggested via cosmochemical, geochemical, and geophysical evidence (17). To ascertain the identity and exact amount of light elements needed in the Earth's inner core, one key piece of information lies in the comparison of the seismic V P − ρ profiles with reliable laboratory measurements of these properties for candidate Fe alloys. Potential Fe-light element alloy must have V P − ρ profiles that match seismic models such as the Preliminary Reference Earth Model and AK135 (7,8). Thus, this requires precise experimental results describing the V P − ρ relationships of Fe alloys at pressure-temperature (P-T) conditions relevant to the Earth's core. To address this issue, here, we present new experimental measurements on the V...

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Section: Resultsmentioning

confidence: 99%

“…In addition to the V P − ρ profiles, static XRD and shockcompression studies have provided constraints on the V Φ − ρ relations of Fe alloys (18,29,30,(50)(51)(52)(53)(54)(55)(56)(57) (Fig. 3C).…”

Section: Resultsmentioning

confidence: 99%

Sound velocities of Fe and Fe-Si alloy in the Earth’s core

Mao

Lin

Liu

et al. 2012

Proc. Natl. Acad. Sci. U.S.A.

Self Cite

101

138

View full text Add to dashboard Cite

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“…According to the work, 1% density deficit can be considered by either 1.69 wt% Si or 0.73 wt% O at the iron melting temperature of 6350 K at the inner and the outer core boundary [Alfè, 2009]. Similar value for Si is also given by Chen et al [2007]. Thus the amounts of O and Si inferred above would create a density deficit of 2.9/1.69+2.6/0.73=5.5% in the outer core, quite similar to the value of Anderson and Isaak [2002] based on equation of state calculations.…”

Section: Resultsmentioning

confidence: 59%

Partitioning of Si and O between liquid iron and silicate melt: A two‐phase ab‐initio molecular dynamics study

Zhang

Guo

2009

Geophysical Research Letters

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The magma ocean process in the early history of the Earth has a great influence on the light element identities and contents of the core which subsequently affect the energy of the geodynamo provided by the compositional convection and the inner core growth through their effect on the phase diagram of iron alloy. In the present work, a two‐phase ab‐initio molecular dynamics method is established to study the solubility of silicon and oxygen in liquid iron in equilibrium with silicate melt. The ab‐initio results are found to be in close agreement with experimental data. At the base of a deep magma ocean (39 GPa and 3116 K), liquid iron contains 2.7 wt% silicon and 0.5 wt% oxygen at the current bulk Earth composition. The oxygen content is low compared with its current estimate in the core, indicating a deeper magma ocean may need to be invoked.

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“…Bcc Fe-based composition models containing silicon [6,7], sulphur [7], and nickel [8] alloying elements can reproduce the density deficit [9] of the inner core. However, none of these composition models show agreement in other physical properties of the inner core, as given in the Preliminary Reference Earth Model [10].…”

Section: Introductionmentioning

confidence: 99%

Thermo-physical properties of body-centered cubic iron–magnesium alloys under extreme conditions

Kádas

Ahuja

Johansson

et al. 2011

Solid State Communications

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This is an author produced version of a paper published in Solid State Communications. This paper has been peer-reviewed but does not include the final publisher proof-corrections or journal pagination. AbstractUsing density functional theory formulated within the framework of the exact muffin-tin orbitals method, we investigate the thermo-physical properties of body-centered cubic (bcc) iron-magnesium alloys, containing 5 and 10 atomic % Mg, under extreme conditions, at high pressure and high temperature. The temperature effect is taken into account via the Fermi-Dirac distribution of the electrons. We find that at high pressures pure bcc iron is dynamically unstable at any temperature, having a negative tetragonal shear modulus (C ′ ). Magnesium alloying significantly increases C ′ of Fe, and bcc Fe-Mg alloys become dynamically stable at high temperature. The electronic structure origin of the stabilization effect of Mg is discussed in details. We show that the thermo-physical properties of a bcc Fe-Mg alloy with 5% Mg agree well with those of the Earth's inner core as provided by seismic observations.

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Thermal expansion of iron-rich alloys and implications for the Earth's core

Cited by 41 publications

References 44 publications

Sound velocities of Fe and Fe-Si alloy in the Earth’s core

Sound velocities of Fe and Fe-Si alloy in the Earth’s core

Partitioning of Si and O between liquid iron and silicate melt: A two‐phase ab‐initio molecular dynamics study

Thermo-physical properties of body-centered cubic iron–magnesium alloys under extreme conditions

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