Diffusion of Siderophile Elements in Fe-Ni Alloys at High Temperature and 10GPa

Diffusivities of siderophile elements in an iron-nickel alloy comparable to model composition of the earth's core, (90%Fe and 10%Ni), have been obtained at temperatures ranging from 1400° C-1600° C and 10 GPa through experiments in a multi-anvil apparatus. Alloys were prepared by synthesizing mixtures of pure metal powders in a piston cylinder at 1400° C and 1GPa. The resulting homogeneous alloys were then sectioned into wafers approximately 1mm thick, and the faces were polished to prepare for diffusion experiments. Diffusion couple experiments were conducted by mating a pure alloy wafer and a doped wafer, and placing the couple directly into a MgO sleeve for pressurization and heating in the multi-anvil apparatus. The duration of the diffusion experiments ranged from 0.5 hours to 48 hours. Upon run completion, the couples were extracted, sectioned lengthwise, and polished for analysis. Diffusion profiles were measured using an electron microprobe. Preliminary results of these experiments show that the diffusivities of Au and Pd are slowed by approximately an order of magnitude when pressure is increased from 1GPa to 10 GPa. It is recognized that diffusion of siderophile elements in the metal phase could be an important rate-limiting factor in partitioning behavior. These preliminary results will lead to a more comprehensive understanding of siderophile diffusion in iron-rich metal and could help in placing important time constraints on element partitioning and possibly on models of core formation. It could also aid in understanding the siderophile element distribution observed in nature, in both terrestrial and extra-terrestrial materials.