Abstract
The Earth's core is primarily composed of iron-nickel alloy with some light elements. These light elements aid in convection in the Earth's liquid outer core, generating the magnetic field. For understanding how these light elements influence the transport properties of liquid iron alloy, we examine diffusion and viscosity of liquid iron along Fe-C/N binary systems. We explore pressures up to 360 GPa and temperatures between 4000 and 7000 K using first-principles molecular dynamics simulations. We explore light element concentrations ranging between approximately 16 and 42 mol%. Our preliminary results show that the viscosity of liquid iron along the outer core adiabat ranges from 0.01-0.015 Pa s, and the presence of light elements slightly reduces viscosity. The effect of temperature is more pronounced than the effect of light elements (C/N) on the viscosity. For the liquid Fe-C with approximately 4 wt.% dissolved carbon, the viscosity decreases by 10-15% at outer core conditions. We find that iron diffuses faster with increasing concentration of light element for Fe- C/N binary alloys. At the core mantle boundary, Fe diffusion in pure liquid iron is 4 X 10 (super -9) m (super 2) s (super -1) . At similar P-T conditions, Fe diffusion is approximately 5-7 X 10 (super -9) m (super 2) s (super -1) for Fe-C/N alloy with 31 mol% of C/N. We find a correlation between enhanced iron mobility and changes in the Fe-Fe coordination number. The average Fe-Fe coordination number in volatile free molten iron is approximately 13. In contrast, the average Fe-Fe coordination number ranges between 11 and 9 as the nitrogen concentration increases from 23 to 42 mol%. The average Fe-Fe coordination number ranges between 12 and 10 as the carbon concentration increases from 16 to 31 mol%. The rate of diffusion for both carbon and nitrogen in Fe-C/N melts are similar and faster than iron. Acknowledgements: Authors would like to acknowledge the US NSF awards: EAR 1753125 and EAR 1763215.