Electrical resistivity of liquid Fe to 12 GPa: Implications for heat flow in cores of terrestrial bodies

Abstract

Electrical and thermal transport properties of liquid Fe under high pressure have important implications for the dynamics and thermal evolution of planetary cores and the geodynamo. However, electrical resistivity (ρ) and thermal conductivity (k) of liquid Fe at high pressure still remain contentious properties. To date, only two experimental investigations of ρ of liquid Fe in the pressure region below 7 GPa are reported in literature. Here we report the results of measurements of ρ for solid and liquid Fe (inversely proportional to k through the Wiedemann-Franz law) at pressures from 3 to 12 GPa, using a large multi-anvil press. We show that ρ of liquid Fe decreases as a function of pressure up to the δ-γ-liquid triple point at ~5.2 GPa, and subsequently remains invariant from 6 to 12 GPa, which is consistent with an earlier study on liquid Ni. Our results demonstrate an important effect of solid phase on the structure and properties of liquid Fe. Our values of ρ for solid and liquid Fe are used to calculate k in Mercury's solid inner core and along the adiabat in the liquid outer cores of Moon, Ganymede, Mercury and Mars. Our robust values of thermal conductivity place the focus on uncertainties in thermal expansion as the cause of variation in values of core conducted heat. Except for Mercury, our adiabatic heat flux values in these terrestrial cores validate the use of similar values used in several previous studies. Our high values of core adiabatic heat flux in Mercury would provide a stabilizing effect on, and lead to an increase in thickness of, the thermally stratified layer at the top of the core.