Thermal conductivity of iron and nickel during melting: Implication to the planetary liquid outer core

We report the measurements of the thermal conductivity (κ) of iron (Fe) and nickel (Ni) at high pressures and high temperatures near the core–mantle boundary (CMB) of Mercury and Mars. κ values are estimated from the temperature measurements across the sample surface in a laser-heated diamond anvil cell (LHDAC) and using the COMSOL software. In both metals, values of κ drop suddenly at the melting temperature and can be used as another helpful technique to estimate melting temperatures at high pressures. We have obtained the thermal conductivity values of Fe and Ni at the CMB of Mercury to be about (60-70) ± 28 W m^-1 K^-1 and (65-70) ± 28 W m^-1 K^-1, respectively. Similarly, in the case of Mars CMB pressure and temperature conditions, the thermal conductivities of Fe and Ni are found to be 80 ± 32 W m^-1 K^-1 and (65-70) ± 28 W m^-1 K^-1, respectively. Using the obtained thermal conductivity values of Fe and Ni, we have estimated the adiabatic heat conduction at the outer core of Mercury and Mars, to be about (59-69) ± 28 mW m^-2 and (61-72) ± 29 mW m^-2 , respectively. Both these values are much larger than the values predicted recently from the estimation of electronic thermal conductivity. (author)