Interdiffusion of Earthʹs core materials to 65 GPa and 2200 K

Diffusion of iron and nickel in an Fe64Ni36 alloy was measured via the use of focused-ion-beam (FIB) milling and energy dispersive x-ray spectroscopy (EDX) to 65 GPa and ∼2200 K. The experiments were performed using a combination of micro-fabricated samples in the laser-heated diamond-anvil cell (DAC), increasing the pressure range for experimentally determined interdiffusion coefficients in FeNi alloys by >40 GPa. Diffusivity in the iron–nickel system follows a homologous temperature relationship D=D0 exp(−19.3(2.7)Tm/T) where D0 is 4.6(7)×10−4 m2 s−1, with zero-pressure activation energy, 301(40) kJ mol−1, consistent with measurements at lower pressures. At inner core conditions, this predicts an inner core solid-state diffusivity of 1×10−14 m2 s−1 (Tm/T=0.95), with an inner core viscosity of 1020–1022 Pa s assuming power-law creep (n=3) with a deviatoric stress of 103–104 Pa.