scholarly journals Review of Electrical Resistivity Measurements and Calculations of Fe and Fe-Alloys Relating to Planetary Cores

2021 ◽  
Vol 9 ◽  
Author(s):  
Meryem Berrada ◽  
Richard A. Secco
Keyword(s):  
Electrical Resistivity ◽  
Boundary Conditions ◽  
Inner Core ◽  
Earth’S Core ◽  
Earth's Core ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
Direct Measurements ◽  
Core Boundary ◽  
Core Conditions

There is a considerable amount of literature on the electrical resistivity of iron at Earth’s core conditions, while only few studies have considered iron and iron-alloys at other planetary core conditions. Much of the total work has been carried out in the past decade and a review to collect data is timely. High pressures and temperatures can be achieved with direct measurements using a diamond-anvil cell, a multi-anvil press or shock compression methods. The results of direct measurements can be used in combination with first-principle calculations to extrapolate from laboratory temperature and pressure to the relevant planetary conditions. This review points out some discrepancies in the electrical resistivity values between theoretical and experimental studies, while highlighting the negligible differences arising from the selection of pressure and temperature values at planetary core conditions. Also, conversions of the reported electrical resistivity values to thermal conductivity via the Wiedemann-Franz law do not seem to vary significantly even when the Sommerfeld value of the Lorenz number is used in the conversion. A comparison of the rich literature of electrical resistivity values of pure Fe at Earth’s core-mantle boundary and inner-core boundary conditions with alloys of Fe and light elements (Si, S, O) does not reveal dramatic differences. The scarce literature on the electrical resistivity at the lunar core suggests the effect of P on a wt% basis is negligible when compared to that of Si and S. On the contrary, studies at Mercury’s core conditions suggest two distinct groups of electrical resistivity values but only a few studies apply to the inner-core boundary. The electrical resistivity values at the Martian core-mantle boundary conditions suggest a negligible contribution of Si, S and O. In contrast, Fe-S compositions at Ganymede’s core-mantle boundary conditions result in large deviations in electrical resistivity values compared to pure Fe. Contour maps of the reported values illustrate ρ(P, T) for pure Fe and its alloys with Ni, O and Si/S and allow for estimates of electrical resistivity at the core-mantle boundary and inner-core boundary conditions for the cores of terrestrial-like planetary bodies.

Hydromagnetic spin-up under conditions of the earth's core-mantle boundary

1978 ◽  
Vol 22 (3) ◽  
pp. 276-282
Author(s):  
Jozef Brestenský ◽  
Gustáv Siráň ◽  
I. Cupal
Keyword(s):  
Earth’S Core ◽  
Earth's Core ◽  
Mantle Boundary ◽  
Core Mantle Boundary

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

2018 ◽  
Vol 46 (1) ◽  
pp. 47-66 ◽  
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.

scholarly journals The flow at the Earth's core-mantle boundary under weak prior constraints

2016 ◽  
Vol 121 (3) ◽  
pp. 1343-1364 ◽  
Author(s):  
Julien Baerenzung ◽  
Matthias Holschneider ◽  
Vincent Lesur
Keyword(s):  
Earth’S Core ◽  
Earth's Core ◽  
Mantle Boundary ◽  
Core Mantle Boundary

scholarly journals Amorphous boron oxide at megabar pressures via inelastic X-ray scattering

2018 ◽  
Vol 115 (23) ◽  
pp. 5855-5860 ◽  
Author(s):  
Sung Keun Lee ◽  
Yong-Hyun Kim ◽  
Paul Chow ◽  
Yunming Xiao ◽  
Cheng Ji ◽  
...  
Keyword(s):  
Oxide Glass ◽  
X Rays ◽  
Oxide Glasses ◽  
Earth’S Core ◽  
Earth's Core ◽  
X Ray ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
X Ray Scattering ◽  
Ray Scattering

Structural transition in amorphous oxides, including glasses, under extreme compression above megabar pressures (>1 million atmospheric pressure, 100 GPa) results in unique densification paths that differ from those in crystals. Experimentally verifying the atomistic origins of such densifications beyond 100 GPa remains unknown. Progress in inelastic X-ray scattering (IXS) provided insights into the pressure-induced bonding changes in oxide glasses; however, IXS has a signal intensity several orders of magnitude smaller than that of elastic X-rays, posing challenges for probing glass structures above 100 GPa near the Earth’s core–mantle boundary. Here, we report megabar IXS spectra for prototypical B2O3 glasses at high pressure up to ∼120 GPa, where it is found that only four-coordinated boron ([4]B) is prevalent. The reduction in the [4]B–O length up to 120 GPa is minor, indicating the extended stability of sp3-bonded [4]B. In contrast, a substantial decrease in the average O–O distance upon compression is revealed, suggesting that the densification in B2O3 glasses is primarily due to O–O distance reduction without the formation of [5]B. Together with earlier results with other archetypal oxide glasses, such as SiO2 and GeO2, the current results confirm that the transition pressure of the formation of highly coordinated framework cations systematically increases with the decreasing atomic radius of the cations. These observations highlight a new opportunity to study the structure of oxide glass above megabar pressures, yielding the atomistic origins of densification in melts at the Earth’s core–mantle boundary.

Influence of thermochemical piles on topography at Earth's core–mantle boundary

2007 ◽  
Vol 261 (3-4) ◽  
pp. 443-455 ◽  
Author(s):  
Teresa Mae Lassak ◽  
Allen K. McNamara ◽  
Shijie Zhong
Keyword(s):  
Earth’S Core ◽  
Earth's Core ◽  
Mantle Boundary ◽  
Core Mantle Boundary

Antipodal observations of global differential times of diffracted P and PKPAB within the D″ layer above Earth's core–mantle boundary

2020 ◽  
Vol 222 (1) ◽  
pp. 327-337
Author(s):  
Rhett Butler ◽  
Seiji Tsuboi
Keyword(s):  
Seismic Velocity ◽  
Compressional Wave ◽  
Polar Phase ◽  
Apparent Velocity ◽  
Earth’S Core ◽  
Earth's Core ◽  
Mantle Boundary ◽  
Core Mantle Boundary ◽  
Velocity Constraints ◽  
Global Mean

SUMMARY Antipodal diffracted, compressional wave (Pdiff) data analysed diametrically opposite three large earthquakes have uniformly sampled 99% of the laterally heterogeneous zone above Earth's core–mantle boundary (D″ in seismic nomenclature). These antipodal data offer a fundamental gross Earth datum—a robust, global constraint on the average compressional velocity at the base of the mantle. We use for the first time the seismic phase PKPAB as a reference, which travels an identical mantle path as Pdiff, thereby cancelling common mantle heterogeneity. Differential traveltimes between Pdiff, PKPAB and PKIKP are measured, appropriately making allowance for the phase shifts acquired in propagation. We have independently confirmed the $\pi /4$ polar phase shift of Pdiff at the antipode. The global mean PKPAB − Pdiff time is 136.5 ± 0.6 s. The global mean apparent velocity (13.05 km s−1) and ray parameter (4.65 ± 0.01 s deg−1) are within the margin of error of prior Pdiff studies—which were dominated by Northern Hemisphere paths—indicating that complementary, southern hemisphere paths have a comparable, mean Pdiff apparent velocity. The seismic velocity constraints afforded by antipodal Pdiff and PKPAB suggest that the heterogeneous processes already observed in D″ may be broadly ascribed where D″ coverage has been lacking or poorly resolved.

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