4:30 PM - 4:45 PM
[SIT06-23] Preliminary result on iron self-diffusion in ε-iron
In this study, by using sintered diamond anvils, we conducted diffusion experiments at pressure ~50 GPa in a Kawai-type multianvil apparatus, “6-axis press”, installed at Okayama University, In the experiments, the natural isotopic iron and 54Fe enriched iron was used as diffusion couple. On the recovered sample after diffusion annealing, diffusion profiles were obtained by the isotope imaging technique using SIMS1270 at Hokkaido University.
Diffusion coefficient at 1400 K was determined to be ~10-17 m2/s in the present study although our result at present is preliminary one because diffusion length is small compared with the length of convolution effect and data is limited. The obtained value is 2-3 order smaller than self-diffusion coefficient in γ-iron at same temperature but ambient pressure. When homologous temperature scaling is applied, diffusion coefficient in the inner core condition is estimated to be ~1013 m2/s by using T/Tm = 0.9 (where Tm is melting temperature) and melting curve of iron (Anzellini et al., 2013). The estimated diffusion coefficient suggests that Harper-Dorn creep may be the dominant deformation mechanism among dislocation creep, diffusion creep and Harper-Dorn creep. Assuming the dominant of Harper-Dorn creep, viscosity of the inner core is calculated to be 1012 Pas consistent with previous estimations based on mineral physics (Van Orman, 2004) and geophysics (Buffett, 1997). In the future work, effect of light element on diffusion will be investigated to understand the origin of the heterogeneity observed in seismology.
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