HR: 0800h
AN: V31B-0617 [Abstracts]
TI: The Effect of Composition on Diffusion of Au in Fe and Fe-Ni Alloys
AU: * Johanesen, K E
EM: johanese@stu.beloit.edu
AF: Department of Geology Beloit College, 700 College St., Beloit, WI 53511
United States
AU: Watson, H C
EM: h.watson@gl.ciw.edu
AF: Geophysical Laboratory Carnegie Institution of Washington, 5251 Broad Branch Rd. NW, Washington, DC
20015
United States
AU: Fei, Y
EM: fei@gl.ciw.edu
AF: Geophysical Laboratory Carnegie Institution of Washington, 5251 Broad Branch Rd. NW, Washington, DC
20015
United States
AB:
Understanding siderophile element diffusion in Fe-Ni alloys will lead to tighter constraints on processes such as meteoritic
body cooling rates, and inner core-outer core communication. Recent studies have determined the effect of temperature and
pressure on diffusion in this system, but the effect of composition has not yet been explored adequately. The effect of Ni
content on Au diffusion in an Fe-Ni system was explored for Fe-Ni alloys with concentrations of 0, 20, and 30 wt. % Ni.
Diffusion couple experiments were conducted using a piston cylinder press at 1 GPa and temperatures ranging from 1150°C
to 1400°C. Concentration profiles were measured by electron microprobe and were fitted to the linear diffusion solution
for an semi-infinite diffusion couple to extract diffusion coefficients (D) using a non-linear least squares fit routine. As
predicted, D increases with Ni content and also with temperature. The diffusivities ranged from 2.06×10-9 at
1150°C to 5.76×10-8 at 1350°C for 0 wt. % Ni; 5.17×10-9 at 1150° C to 1.93×10-7
at 1400°C for 20 wt. % Ni; and 2.41×10-8 at 1150°C to 2.13×10-7 at 1400°C for 30 wt. %
Ni. As temperature increases, the effect of Ni on diffusion rates increases, implying a possible change in diffusion
mechanism between 1250°C and 1300°C. Ni appears to have a negligible effect at lower temperatures, which would
indicate that Ni may not need to be considered when modeling siderophile trace element diffusion rates in iron meteorites.
DE: 1000 GEOCHEMISTRY
DE: 1015 Composition of the core
DE: 1028 Composition of meteorites (3662, 6240)
DE: 3630 Experimental mineralogy and petrology
DE: 5120 Plasticity, diffusion, and creep
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005