Electrical resistivity and thermal conductivity of hcp Fe–Ni alloys under high pressure: Implications for thermal convection in the Earth’s core

Abstract

We measured the electrical resistivity of Fe–Ni alloys (iron with 5, 10, and 15wt.% nickel) using four-terminal method in a diamond-anvil cell up to 70GPa at 300K. The results demonstrate that measured resistivity increases linearly with increasing nickel impurity concentration, as predicted by the Matthiessen’s rule. The impurity resistivity is predominant at ambient temperature; the incorporation of 5wt.% nickel into iron doubles the electrical resistivity at 60GPa. Such impurity effect becomes minor at high temperature of the Earth’s core because of the resistivity “saturation”. We also calculated that >0.9TW heat flow is necessary at the top of the inner core for thermal convection in the inner core. It requires the CMB heat flow of ∼30TW, which is much higher than recent estimates of 5–15TW. This means that purely thermal convection does not occur in the inner core.