Experimental determination of oxygen diffusion in liquid iron at high pressure

Posner, Esther S.; Rubie, D. C.; Frost, Daniel J.; Steinle‐Neumann, Gerd

doi:10.1016/j.epsl.2017.02.020

Cited by 21 publications

(31 citation statements)

References 35 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…In general, calculated D Fe values are 2–4 times slower that D O , consistent with previous studies on liquid iron alloys with low oxygen contents ( X O ≲ 0.2) [ Pozzo et al , ; Ichikawa and Tsuchiya , ]. Low pressure results are in good agreement with experimental oxygen diffusion data at 7 GPa [ Posner et al , ].…”

Section: Resultssupporting

confidence: 90%

“…Additionally, experiments and computations on the diffusivities of Si and Fe show the expected behavior of a reasonably strong pressure dependence, as expressed through their activation volumes (Δ V ~ 0.4 cm 3 mol −1 ) [ Posner et al , ], defined as

\frac{\partial ln D}{\partial P} = - \frac{normalΔ V}{RT},

where D is the diffusion coefficient and R is the universal gas constant. By contrast, oxygen diffusion experiments up to 18 GPa show a negligible pressure effect (Δ V = 0.1 ± 0.1 cm 3 mol −1 ) [ Posner et al , ] and a computational study on the transport and structural properties of Fe–FeO liquid reports only a slightly larger pressure effect (Δ V ~ 0.3 cm 3 mol −1 ) [ Ichikawa and Tsuchiya , ]. However, the simulations were conducted at pressures above 100 GPa only, which is far beyond the pressure range accessible in the experiments and therefore provide little basis for a reasonable comparison.…”

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Structural changes and anomalous self‐diffusion of oxygen in liquid iron at high pressure

Posner

Steinle‐Neumann

Vlček

et al. 2017

Geophysical Research Letters

Self Cite

View full text Add to dashboard Cite

We report structural properties and diffusivity of liquid Fe0.96O0.04 over a density range of 5.421–11.620 g cm−3, corresponding to pressures of 0–330 GPa and 2200–5500 K, using first‐principles molecular dynamics. We predict a change in compression mechanism near 8 g cm−3. At lower density, Fe and O coordinations increase from ~10 to ~13 and ~3 to ~6, respectively, the average Fe–O distance increases from ~1.81 Å to ~1.88 Å, and the Fe–Fe distance remains essentially constant. Calculated oxygen diffusivities, DO, remain constant over the corresponding pressure range, consistent with experiments. For larger densities, interatomic distances and diffusion rates for both species decrease monotonically. Oxygen coordination reaches a maximum of ~8.5 at ~9.4 g cm−3, indicating a local B2 packing for Fe around O under conditions of the Earth's core. The pressure‐induced structural evolution provides an explanation for a previously reported change in pressure dependence of oxygen solubility in liquid iron.

show abstract

Section: Resultssupporting

confidence: 90%

\frac{\partial ln D}{\partial P} = - \frac{normalΔ V}{RT},

Section: Introductionmentioning

confidence: 99%

Structural changes and anomalous self‐diffusion of oxygen in liquid iron at high pressure

Posner

Steinle‐Neumann

Vlček

et al. 2017

Geophysical Research Letters

Self Cite

View full text Add to dashboard Cite

show abstract

“…Diffusion of hydrogen in the liquid core is much faster than in solid silicates. Our nominal value for its diffusivity in the core is D H,C = 1.2 × 10 −7 m 2 /s, which is 20 times the diffusivity of oxygen in liquid iron at 20 GPa and 2000 K inferred from recent experiments (Posner et al, ). The plausible range for D H,C extends from ~1.4 × 10 −7 m 2 /s as measured at ~1873 K and ambient pressure (Depuydt & Parlee, ) to ~8 × 10 −8 m 2 /s for Earth's core at 4400 K and 130 GPa from first‐principles calculations (Umemoto & Hirose, ).…”

Section: Theory and Numerical Methodsmentioning

confidence: 74%

Hydrogenation of the Martian Core by Hydrated Mantle Minerals With Implications for the Early Dynamo

O’Rourke

Shim

2019

JGR Planets

View full text Add to dashboard Cite

Mars lacks an internally generated magnetic field today. Crustal remanent magnetism and meteorites indicate that a dynamo existed after accretion but died roughly four billion years ago. Standard models rely on core/mantle heat flow dropping below the adiabatic limit for thermal convection in the core. However, rapid core cooling after the Noachian is favored instead to produce long‐lived mantle plumes and magmatism at volcanic provinces such as Tharsis and Elysium. Hydrogenation of the core could resolve this apparent contradiction by impeding the dynamo while core/mantle heat flow is superadiabatic. Here we present parameterized models for the rate at which mantle convection delivers hydrogen into the core. Our models suggest that most of the water that the mantle initially contained was effectively lost to the core. We predict that the mantle became increasingly ironrich over time and a stratified layer awaits detection in the uppermost core—analogous to the E′ layer atop Earth's core but likely thicker than alternative sources of stratification in the Martian core such as iron snow. Entraining buoyant, hydrogen‐rich fluid downward in the core subtracts gravitational energy from the total dissipation budget for the dynamo. The calculated fluxes of hydrogen are high enough to potentially reduce the lifetime of the dynamo by several hundred million years or longer relative to conventional model predictions. Future work should address the complicated interactions between the stratified, hydrogen‐rich layer and convection in the underlying core.

show abstract

“…Several previous studies (e.g., Posner, Rubie, Frost, & Steinle‐Neumann, ; Rubie et al, ; Samuel, ) report that a centimeter‐scale maximum radius of iron‐rich metallic droplets (e.g., diffusion distance

\propto \sqrt{D}

) is required to achieve full metal‐silicate equilibration assuming a diffusion coefficient D ~ 10 −8 m 2 ·s −1 . As we demonstrate here, the kinetics of chemical equilibration depends on the species ϕ, and shorter (longer) equilibration times are required for alloying elements with faster (slower) D ϕ .…”

Section: Implications For Planetary Coresmentioning

confidence: 99%

Mass Transport and Structural Properties of Binary Liquid Iron Alloys at High Pressure

Posner

Steinle‐Neumann

2019

Geochem Geophys Geosyst

Self Cite

View full text Add to dashboard Cite

We determine mass transport and structural properties of binary liquid iron alloys over a wide density (5.055–11.735 g·cm−3) and temperature range (2,500–6,500 K) using first‐principles molecular dynamics. Compositions consist of 96 at% Fe and 4 at% ϕ, where ϕ = H, C, N, O, Mg, Si, S, or Ni. Self‐diffusion coefficients (D) of Fe and ϕ range from 3.5·10−9 to 1.9·10−7 m2·s−1. Results show a relation between mean atomic radius and diffusivity ratio for the alloying element and iron: Si and Ni are “iron‐like” with similar atomic radii and D compared with those of Fe; H, C, N, O, and S are “small non‐iron‐like” with smaller atomic radii and larger D; and Mg transitions from “large non‐iron‐like” with a larger atomic radius and smaller D at low density to iron‐like under conditions of the Earth's core. The effect of pressure on D for C, N, and O is negligible for densities below ~8 g·cm−3, accompanied by an increase in average coordination numbers to ~6, and an increase in mean atomic radii. For densities above ~8 g·cm−3, diffusivities and atomic radii of these elements decrease monotonically with pressure, which is typical for the iron‐like alloying elements as well as for H, Mg, and S over the whole compression range. While atomic radius ratios move toward unity with compression, diffusivity ratios for the alloying element relative to iron tend to increase for the “non‐iron‐like” elements with density.

show abstract

Experimental determination of oxygen diffusion in liquid iron at high pressure

Cited by 21 publications

References 35 publications

Structural changes and anomalous self‐diffusion of oxygen in liquid iron at high pressure

Structural changes and anomalous self‐diffusion of oxygen in liquid iron at high pressure

Hydrogenation of the Martian Core by Hydrated Mantle Minerals With Implications for the Early Dynamo

Mass Transport and Structural Properties of Binary Liquid Iron Alloys at High Pressure

Contact Info

Product

Resources

About