Electrical and thermal transport properties of iron and iron-silicon alloy at high pressure

► Electrical and thermal transport properties of iron and iron-silicon alloy at high pressure

The efficiency of heat transfer by conduction in the Earth's core controls the dynamics of convection and limits the power available for the geodynamo. We have measured the room temperature electrical resistivity of iron and iron-silicon alloy to 60 GPa and present a new model of the resistivity at high pressures and temperatures relevant to the Earth's core. The model is compared with available shock wave data and theoretical studies. For a power law and linear temperature dependence of electrical resistivity, the calculated thermal conductivity at the core-mantle boundary is ~67–145 W/m/K for pure Fe and ~41–60 W/m/K for Fe–9 wt % Si. Impurities in the core have a strong effect on the transport properties of iron that could significantly impact core thermal models. The models describing the data indicate higher thermal conductivity at core pressure than previously suggested, requiring additional energy sources in the past to operate the geodynamo.

 (a) Experimental geometry of Experiment 1. (b) Photomicrograph of Experiment 1 viewed through the top anvil in Figure 1a in reflected and transmitted light at ~50 GPa. A cubic boron nitride insert was transparent at this pressure, and the Pt electrical leads are the opaque wedges connecting to the iron sample in the center.

C. Seagle, E. Cottrell, Y. Fei, D.R. Hummer, V.B. Prakapenka, Electrical and thermal transport properties of iron and iron-silicon alloy at high pressure, (2013), Geophys. Res. Lett., v. 40, 1-5, http://dx.doi.org/10.1002/2013GL057930