Interdiffusion of Earth's 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 similar to 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=D-o exp(-19.3(2.7)T-m/T) where D-o is 4.6(7) x 10(-4) m(2) 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 x 10(-14) m(2) s(-1) (T-m/T=0.95), with an inner core viscosity of 10(20)-10(22) Pa s assuming power-law creep (n=3) with a deviatoric stress of 10(3)-10(4) Pa. (C) 2012 Elsevier B.V. All rights reserved.