Electrical Resistivity Measurements of Fe‐Si With Implications for the Early Lunar Dynamo
Meryem Berrada, Richard A. Secco, Wenjun Yong, Joshua A. H. Littleton
Abstract
Abstract The effect of impurities on the electrical resistivity of Fe at core conditions is controversial due to the challenges of measuring transport properties of Fe alloys under high‐pressure and high‐temperature conditions. In this study we describe an innovative technique to make wires of Fe‐Si samples initially in powder form for measuring electrical resistivity. The electrical resistivity of Fe‐2, Fe‐8.5, and Fe‐17 wt%Si was measured at 3, 4, and 5 GPa at temperatures into the liquid state and compared to results of Fe‐4.5 wt%Si and Fe from prior studies. Isothermal electrical resistivity increases linearly with increasing Si content. Yet the effect of Si content on the magnitude of the electrical resistivity compared to that of Fe diminished as temperature increased at all experimental pressures. This implies the contribution to the electrical resistivity due to Si impurities is dependent on temperature, in disagreement with Matthiessen's rule. Thermal conductivity of Fe‐Si alloys calculated using the Wiedemann‐Franz law indicates a nonnegligible influence of the Si content on the thermal conductive properties of Fe‐Si alloys. The results are used to calculate the adiabatic heat flux of an Fe‐Si lunar core and date the end of the high magnetic field intensity era of the lunar dynamo to be in the range 3.32–3.80 Ga.