Viscosity of Fe-Ni-C Liquids up to Core Pressures and Implications for Dynamics of Planetary Cores

The viscosity of iron alloy liquids is the key for the core dynamo and core-mantle differentiation of terrestrial bodies. Here we measured the viscosity of Fe-Ni-C liquids up to 7 GPa using the floating sphere viscometry method and up to 330 GPa using first-principles calculations. We found a viscosity increase at similar to 3-5 GPa, coincident with a structural transition in the liquids. After the transition, the viscosity reaches similar to 14-27 mPa center dot s, a factor of 2-4 higher than that of Fe and Fe-S liquids. Our computational results from 5 to 330 GPa also indicate a high viscosity of the Fe-Ni-C liquids. For a carbon-rich core in large terrestrial body, the level of turbulence in the outer core would be lessened approaching the inner core boundary. It is also anticipated that Fe-Ni-C liquids would percolate in Earth's deep silicate mantle at a much slower speed than Fe and Fe-S liquids.

Automated summary

The viscosity of iron alloy liquids is crucial for the core dynamo and core-mantle differentiation of terrestrial bodies. Through experimental measurements and first-principles calculations, it was found that Fe-Ni-C liquids undergo a structural transition at certain pressures, resulting in an increase in viscosity. The viscosity of Fe-Ni-C liquids is higher than that of Fe and Fe-S liquids, and for a carbon-rich core, the turbulence in the outer core would decrease, and the percolation speed of Fe-Ni-C liquids in the deep silicate mantle would be slower compared to Fe and Fe-S liquids.