11:30 〜 11:45
[SIT21-28] First-principles Investigation of Iron Diffusion Properties with Implications to Inner Core Plasticity
★Invited Papers
キーワード：Inner Core, Self-diffusion, Plasticity
The mechanical properties of Earth’s inner core are key for understanding the evolution and dynamics of the core. However, little is known about the mechanical properties of iron (alloys) at inner core conditions. Therefore, long-standing questions remain open about the viscous strength of the inner core (Yoshida et al., 1996; Karato, 1999), about the origin of its seismic anisotropy (Deuss, 2014) and about its rotational dynamics (Buffett, 1997). All these issues rely on plastic deformation of the inner core, which is barely constrained.
Under extreme conditions of the Earth’s deep interior, plasticity is expected to be rate limited by atomic diffusion. Experimental studies of diffusion in iron-nickel alloys at elevated P,T conditions finally rely on extrapolation to inner core conditions (Yunker and Van Orman, 2007; Reaman et al., 2012). Here, we investigate vacancy diffusion in iron at the appropriate inner core conditions. We use a density functional approach to calculate all quantities entering the diffusion coefficient, including the role of pressure and temperature, and quantify the self-diffusion coefficient of hcp iron according to transition state theory (TST).
Vacancy diffusion controls many deformation mechanisms such as dislocation creep, an effective strain producing mechanism in metals. We derived a creep model (based on Weertman, 1955 and Nabarro, 1967) to quantify the rate limiting bounds of climb-controlled dislocation creep in hcp iron to provide the first theoretical estimates of the inner core viscosity. Our results suggest an inner core viscosity that is significantly lower than that of Earth’s mantle.
Under extreme conditions of the Earth’s deep interior, plasticity is expected to be rate limited by atomic diffusion. Experimental studies of diffusion in iron-nickel alloys at elevated P,T conditions finally rely on extrapolation to inner core conditions (Yunker and Van Orman, 2007; Reaman et al., 2012). Here, we investigate vacancy diffusion in iron at the appropriate inner core conditions. We use a density functional approach to calculate all quantities entering the diffusion coefficient, including the role of pressure and temperature, and quantify the self-diffusion coefficient of hcp iron according to transition state theory (TST).
Vacancy diffusion controls many deformation mechanisms such as dislocation creep, an effective strain producing mechanism in metals. We derived a creep model (based on Weertman, 1955 and Nabarro, 1967) to quantify the rate limiting bounds of climb-controlled dislocation creep in hcp iron to provide the first theoretical estimates of the inner core viscosity. Our results suggest an inner core viscosity that is significantly lower than that of Earth’s mantle.