Pressure Dependence of Melting Temperature of Iron at the Earth’s Core Conditions

AbstractWe summarize the main ideas used to determine the thermodynamic properties of pure systems and binary alloys from first principles calculations. These are based on the ab initio calculations of free energies. As an application we present the study of iron and iron alloys under Earth,s core conditions. In particular, we report the whole melting curve of iron under these conditions, and we put constraints on the composition of the core. We found that iron melts at 6350士600 K at the pressure corresponding to the boundary between the solid inner core and the liquid outer core (ICB). We show that the core could not have been formed from a binary mixture of Fe with S, Si or O and we propose a ternary or quaternary mixture with 8—10% of S/Si in both liquid and solid and an additional ~8% of oxygen in the liquid. Based on this proposed composition we calculate the shift of melting temperature with respect to the melting temperature of pure Fe of ~—700 K, so that our best estimate for the temperature of the Earth's core at ICB is 5650±600 K.

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New high-pressure phases of Fe7N3 and Fe7C3 stable at Earth's core conditions: evidences for carbon–nitrogen isomorphism in Fe-compounds

RSC Advances ◽

10.1039/c8ra09942a ◽

2019 ◽

Vol 9 (7) ◽

pp. 3577-3581 ◽

Cited By ~ 5

Author(s):

Nursultan Sagatov ◽

Pavel N. Gavryushkin ◽

Talgat M. Inerbaev ◽

Konstantin D. Litasov

Keyword(s):

Crystal Structure ◽

High Pressure ◽

Ab Initio ◽

Structure Prediction ◽

Harmonic Approximation ◽

Crystal Structure Prediction ◽

Earth’S Core ◽

Earth's Core ◽

Core Conditions

We carried out ab initio calculations on the crystal structure prediction and determination of P–T diagrams within the quasi-harmonic approximation for Fe7N3 and Fe7C3.

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Thermal and electrical conductivity of solid iron and iron–silicon mixtures at Earth's core conditions

Earth and Planetary Science Letters ◽

10.1016/j.epsl.2014.02.047 ◽

2014 ◽

Vol 393 ◽

pp. 159-164 ◽

Cited By ~ 56

Author(s):

Monica Pozzo ◽

Chris Davies ◽

David Gubbins ◽

Dario Alfè

Keyword(s):

Electrical Conductivity ◽

Earth’S Core ◽

Earth's Core ◽

Iron Silicon ◽

Solid Iron ◽

Core Conditions

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Thermodynamics of hexagonal-close-packed iron under Earth’s core conditions

Physical Review B ◽

10.1103/physrevb.64.045123 ◽

2001 ◽

Vol 64 (4) ◽

Cited By ~ 216

Author(s):

D. Alfè ◽

G. D. Price ◽

M. J. Gillan

Keyword(s):

Earth’S Core ◽

Earth's Core ◽

Hexagonal Close Packed ◽

Core Conditions

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First-principles calculations of properties of orthorhombic iron carbideFe7C3at the Earth's core conditions

Physical Review B ◽

10.1103/physrevb.91.214112 ◽

2015 ◽

Vol 91 (21) ◽

Cited By ~ 12

Author(s):

Zamaan Raza ◽

Nina Shulumba ◽

Nuala M. Caffrey ◽

Leonid Dubrovinsky ◽

Igor A. Abrikosov

Keyword(s):

First Principles ◽

First Principles Calculations ◽

Earth’S Core ◽

Earth's Core ◽

Core Conditions

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The Thermal Conductivity of Earth's Core: A Key Geophysical Parameter's Constraints and Uncertainties

Annual Review of Earth and Planetary Sciences ◽

10.1146/annurev-earth-082517-010154 ◽

2018 ◽

Vol 46 (1) ◽

pp. 47-66 ◽

Cited By ~ 21

Author(s):

Q. Williams

Keyword(s):

Thermal Conductivity ◽

High Pressures ◽

Inner Core ◽

Thermal Evolution ◽

Magnetic Moments ◽

Earth’S Core ◽

Earth's Core ◽

Current State ◽

Core Conditions

The thermal conductivity of iron alloys at high pressures and temperatures is a critical parameter in governing ( a) the present-day heat flow out of Earth's core, ( b) the inferred age of Earth's inner core, and ( c) the thermal evolution of Earth's core and lowermost mantle. It is, however, one of the least well-constrained important geophysical parameters, with current estimates for end-member iron under core-mantle boundary conditions varying by about a factor of 6. Here, the current state of calculations, measurements, and inferences that constrain thermal conductivity at core conditions are reviewed. The applicability of the Wiedemann-Franz law, commonly used to convert electrical resistivity data to thermal conductivity data, is probed: Here, whether the constant of proportionality, the Lorenz number, is constant at extreme conditions is of vital importance. Electron-electron inelastic scattering and increases in Fermi-liquid-like behavior may cause uncertainties in thermal conductivities derived from both first-principles-associated calculations and electrical conductivity measurements. Additional uncertainties include the role of alloying constituents and local magnetic moments of iron in modulating the thermal conductivity. Thus, uncertainties in thermal conductivity remain pervasive, and hence a broad range of core heat flows and inner core ages appear to remain plausible.

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16. Iron at Earth's Core Conditions from First Principles Calculations

Theoretical and Computational Methods in Mineral Physics ◽

10.1515/9781501508448-018 ◽

2010 ◽

pp. 337-354

Author(s):

Dario Alfè

Keyword(s):

First Principles ◽

First Principles Calculations ◽

Earth’S Core ◽

Earth's Core ◽

Core Conditions

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Approaching Earth’s core conditions in high-resolution geodynamo simulations

Geophysical Journal International ◽

10.1093/gji/ggz232 ◽

2019 ◽

Vol 219 (Supplement_1) ◽

pp. S137-S151 ◽

Cited By ~ 6

Author(s):

Julien Aubert

Keyword(s):

Magnetic Field ◽

High Resolution ◽

Large Scale ◽

Small Scale ◽

Low Resolution ◽

Earth’S Core ◽

Earth's Core ◽

Density Anomaly ◽

Core Conditions ◽

The Magnetic Field

SUMMARY The geodynamo features a broad separation between the large scale at which Earth’s magnetic field is sustained against ohmic dissipation and the small scales of the turbulent and electrically conducting underlying fluid flow in the outer core. Here, the properties of this scale separation are analysed using high-resolution numerical simulations that approach closer to Earth’s core conditions than earlier models. The new simulations are obtained by increasing the resolution and gradually relaxing the hyperdiffusive approximation of previously published low-resolution cases. This upsizing process does not perturb the previously obtained large-scale, leading-order quasi-geostrophic (QG) and first-order magneto-Archimedes-Coriolis (MAC) force balances. As a result, upsizing causes only weak transients typically lasting a fraction of a convective overturn time, thereby demonstrating the efficiency of this approach to reach extreme conditions at reduced computational cost. As Earth’s core conditions are approached in the upsized simulations, Ohmic losses dissipate up to 97 per cent of the injected convective power. Kinetic energy spectra feature a gradually broadening self-similar, power-law spectral range extending over more than a decade in length scale. In this range, the spectral energy density profile of vorticity is shown to be approximately flat between the large scale at which the magnetic field draws its energy from convection through the QG-MAC force balance and the small scale at which this energy is dissipated. The resulting velocity and density anomaly planforms in the physical space consist in large-scale columnar sheets and plumes, respectively, co-existing with small-scale vorticity filaments and density anomaly ramifications. In contrast, magnetic field planforms keep their large-scale structure after upsizing. The small-scale vorticity filaments are aligned with the large-scale magnetic field lines, thereby minimizing the dynamical influence of the Lorentz force. The diagnostic outputs of the upsized simulations are more consistent with the asymptotic QG-MAC theory than those of the low-resolution cases that they originate from, but still feature small residual deviations that may call for further theoretical refinements to account for the structuring constraints of the magnetic field on the flow.

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