Thermal conductivity and Seebeck coefficient of Fe and Fe-Si alloys: Implications for variable Lorenz number

Secco, Richard A.

doi:10.1016/j.pepi.2017.01.005

Cited by 63 publications

(71 citation statements)

References 82 publications

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“…The Lorenz ratio approaches the Sommerfeld derivation L 0 , 2.44 × 10 −8 WK 2 , provided that the thermal conductivity is purely electronic, the electron gas is highly degenerate, and the relaxation time is the same for electrical and thermal conduction (Klemens, ). The deviation of the Lorenz ratio has been observed for Fe alloys (de Koker et al, ; Secco, ). In metallic alloys such as Fe‐S, the thermal transport is a complex process due to the coexistence of electron and phonon conduction.…”

Section: Methodsmentioning

confidence: 80%

Thermal Conductivity of FeS and Its Implications for Mercury's Long‐Sustaining Magnetic Field

et al. 2019

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The MESSENGER mission revealed that Mercury's magnetic field might have operated since 3.7–3.9 Ga. While the intrinsic magnetism suggests an active dynamo within Mercury's core, the mechanism that is responsible for sustaining the dynamo for prolonged period of time remains unknown. Here we investigated the electrical conductivity of Fe‐S alloys at pressure of 8 GPa and temperatures up to 1,700 K. We show that the electrical conductivity of Fe‐S alloys at 1,500 K is about 103 S/m, 2 orders of magnitude lower than the previously assumed value for dynamo calculations. The thermal conductivity was estimated using the Wiedemann‐Franz law. The total thermal conductivity of FeS is estimated to be ~4 Wm/K at the Mercurian core‐mantle boundary conditions. The low thermal conductivity suggests that a thermally driven dynamo operating on Mercury is more likely than expected. If coupled with chemical buoyancy sources, it is possible to sustain an intrinsic dynamo during time scales compatible with the MESSENGER observations.

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Section: Methodsmentioning

confidence: 80%

Thermal Conductivity of FeS and Its Implications for Mercury's Long‐Sustaining Magnetic Field

et al. 2019

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“…Values of L(T)/L 0 are less than unity in the low temperature range, indicating that if L(T) was used in our calculation, the thermal conductivity values calculated with our experimental resistivity values would be even lower than those plotted in the low temperature range. However, in the higher‐ T range, L(T)/L o > 1 for Ni and this is also consistent with Fe as recently discussed [ Secco , ]. The values of the electronic thermal conductivity of Ni display the same general trend as the experimentally obtained total thermal conductivity at atmospheric pressure [ Laubitz et al ., ; Ho et al ., ].…”

Section: Resultsmentioning

confidence: 99%

“…The experiments were carried out using a 3000 t multianvil large volume press with the capability of fully automated pressure control and adjustable rates of heating. The technical details of the press and its pressure calibration at room and high T have been described elsewhere [Secco andYong, 2012, 2016;Secco and Sukara, 2016]. Detailed expositions on the multianvil pressure cell design, materials, properties, and applications have been given by others [Frost et al, 2004;Leinenweber et al, 2012;Shatskiy et al, 2011].…”

Section: Methodsmentioning

confidence: 99%

Constant electrical resistivity of Ni along the melting boundary up to 9 GPa

Silber

Secco

2017

JGR Solid Earth

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Characterization of transport properties of liquid Ni at high pressures has important geophysical implications for terrestrial planetary interiors, because Ni is a close electronic analogue of Fe and it is also integral to Earth's core. We report measurements of the electrical resistivity of solid and liquid Ni at pressures 3–9 GPa using a 3000 t multianvil large volume press. A four‐wire method, in conjunction with a rapid acquisition meter and polarity switch, was used to overcome experimental challenges such as melt containment and maintaining sample geometry and to mitigate the extreme reactivity/solubility of liquid Ni with most thermocouple and electrode materials. Thermal conductivity is calculated using the Wiedemann‐Franz law. Electrical resistivity of solid Ni exhibits the expected P dependence and is consistent with earlier experimental values. Within experimental uncertainties, our results indicate that resistivity of liquid Ni remains invariant along the P‐dependent melting boundary, which is in disagreement with earlier prediction for liquid transition metals. The potential reasons for such behavior are examined qualitatively through the impact of P‐independent local short‐range ordering on electron mean free path and the possibility of constant Fermi surface at the onset of Ni melting. Correlation among metals obeying the Kadowaki‐Woods ratio and the group of late transition metals with unfilled d‐electron band displaying anomalously shallow melting curves suggests that on the melting boundary, Fe may exhibit the same resistivity behavior as Ni. This could have important implications for the heat flow in the Earth's core.

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“…Our experimental results show that these competing effects appear to offset each other on the P ‐ and T ‐dependent melting boundary. In the approach to solving the linearized Boltzmann equation that uses the relaxation time approximation, the kinetic coefficients are defined (e.g., Secco, ). The Boltzmann equation is a description of the steady state, whereas the relaxation time specifies how the system returns to equilibrium.…”

Section: Discussionmentioning

confidence: 99%

Heat Flow in Earth's Core From Invariant Electrical Resistivity of Fe‐Si on the Melting Boundary to 9 GPa: Do Light Elements Matter?

et al. 2019

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The electrical resistivity and thermal conductivity of liquid Fe alloys are the least constrained parameters in Earth's outer core (OC). These parameters are important as they modulate energy budget available for the geodynamo and affect the spatiotemporal evolution of the core. We report results of electrical resistivity measurements on solid and liquid Fe‐4.5 wt%Si from 3–9 GPa using a large volume multianvil press. The internally modified 18/11 octahedron cell was used to maintain the geometry of the liquid sample and to delay the onset of contamination. Electrical resistivity of solid Fe‐4.5Si decreases steadily with pressure and is very sensitive to increasing temperature‐driven onset of phase transitions. Along the melting boundary and within error, electrical resistivity remains constant and assumes the same value of 120 μΩcm as observed in pure liquid Fe. The results are interpreted in the context of icosahedral short‐range order (ISRO) structures that exhibit higher concentration with increasing pressure. Along the melting line, the increasing concentration of ISROs reduces charge carrier mean free path and prevents decrease of electrical resistivity with increasing pressure as seen in liquid metals, Cu, Ag, and Au, which do not have ISROs. In light of recent developments in understanding of the structure and dynamics of liquid transition metals and alloys, we postulate that our findings are applicable to other Fe alloys in the OC with small light element (C, S, and O) content. We calculated an adiabatic heat flow of 9.4–12 TW at the OC‐CMB interface, which admits thermal convection.

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Thermal conductivity and Seebeck coefficient of Fe and Fe-Si alloys: Implications for variable Lorenz number

Cited by 63 publications

References 82 publications

Thermal Conductivity of FeS and Its Implications for Mercury's Long‐Sustaining Magnetic Field

Thermal Conductivity of FeS and Its Implications for Mercury's Long‐Sustaining Magnetic Field

Constant electrical resistivity of Ni along the melting boundary up to 9 GPa

Heat Flow in Earth's Core From Invariant Electrical Resistivity of Fe‐Si on the Melting Boundary to 9 GPa: Do Light Elements Matter?

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