HR: 13:40h
AN: T22D-01    [PDF]
TI: The Effect of Pressure on Diffusion of Au, Pd, and Re in Fe-Ni Alloys
AU: * Watson, H C
EM: watsoh@rpi.edu
AF: Rensselaer Polytechnic Institute, Department of Earth and Environmental Sciences 110 Eighth St., Troy, NY 12180 United States
AU: Fei, Y
EM: y.fei@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington 5251 Broad Branch Rd, NW, Washington, DC 20015 United States
AU: Watson, B
EM: watsoe@rpi.edu
AF: Rensselaer Polytechnic Institute, Department of Earth and Environmental Sciences 110 Eighth St., Troy, NY 12180 United States
AB: It is understood that the core of the earth consists predominantly of an iron-nickel alloy. Diffusion is commonly considered to be a rate limiting step in many processes such as crystal growth as well as element partitioning. It follows that understanding the diffusive behaviour of trace siderophile elements in Fe-Ni alloys could help constrain models of core formation, time and length scales of communication between the inner and the outer core of the earth, and crystallization of the inner core. We measured the effect of pressure on the diffusivity of several siderophile elements (Au, Pd, Re) in solid 90:10 iron-nickel alloy using a multi-anvil pressure device. The elements investigated can be considered to be broadly representative of many siderophile elements. Diffusion couple experiments were conducted at pressures ranging from 5 to 25 GPa, and temperatures ranging from $1200\deg$ C to $1600\deg$ C. Alloys for the diffusion couples were presynthesized by compacting and heating mixtures of pure metal powders in a piston-cylinder device at 1GPa and $1400\deg$ C for 60 hours. The diffusion couples were made by juxtaposing a disk of pure 90%Fe 10%Ni alloy with another disk of a similar alloy doped with up to 2% of the diffusant of interest. The duration of the experiments ranged from 12-120 hours. Diffusion profiles in all experimental products were measured by elctrom microprobe analysis. It was found that there is a substantial decrease in diffusivity with the application of pressure for all three elements, and the magnitude of this decrease appears to be similar for all three elements. The relative diffusivities consistently span about an order of magnitude at any given set of conditions (Au is always ~10x faster than Re, and Pd is intermediate). These are some of the first high pressure data of trace element diffusion in iron nickel alloys, and are part of a broader study with the goal of systematically understanding the general diffusion behaviour of siderophile elements in Fe-Ni alloys at conditions relevant to the earth and other planetary bodies.
DE: 1000 GEOCHEMISTRY (New field, replaces Rock Chemistry)
DE: 1065 Trace elements (3670)
DE: 3924 High-pressure behavior
DE: 5120 Plasticity, diffusion, and creep
DE: 8124 Earth's interior--composition and state (old 8105)
SC: Tectonophysics [T]
MN: 2003 Fall Meeting