Japan Geoscience Union Meeting 2015

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International Session (Oral)

Symbol S (Solid Earth Sciences) » S-IT Science of the Earth's Interior & Techtonophysics

[S-IT06] Early Earth - from accumulation to formation -

Sun. May 24, 2015 11:00 AM - 12:45 PM 303 (3F)

Convener:*Tatsuya Sakamaki(Department of Earth Science, Tohoku University), Akio Suzuki(Department of Earth and Planetary Materials Science, Faculty of Science, Tohoku University), Seiji Kamada(Graduate school of Science, Tohoku University), Bjorn Mysen(Geophysical Laboratory, Carnegie Inst. Washington), Chair:Tatsuya Sakamaki(Department of Earth Science, Tohoku University)

12:30 PM - 12:45 PM

[SIT06-09] Compression of hcp Fe-Si-H alloy to 130 GPa

*Shoh TAGAWA1, Kenji OHTA1, Kei HIROSE2, Yasuo OHISHI3 (1.Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2.Earth-Life Science Institute, Tokyo Institute of Technology, 3.SPring-8, Japan Synchrotron Radiation Research Institute)

Keywords:Light elements, Core formation, Hydorogen, Silicon, High pressure, Diamond anvil cell (DAC)

The light elements in the Earth's core have not been identified yet, but hydrogen is now collecting more attention because recent planet formation theory suggests that large amount of water (e.g. 10 to 100 times seawater) should have been brought to the Earth during the late stage of its formation. Hydrogen is a strong siderophile element and thus it is possibly present in the core. The effect of hydrogen on the property of iron alloy is little known yet. Moreover, the presence of 〜 6 wt.% silicon has been also strongly supported by geochemical and cosmochemical arguments. Here we report hydrogenation of Fe0.88Si0.12 (6.5 wt. % Si) alloy and the compression behavior of Fe0.88Si0.12H0.8 alloy to 130 GPa at room temperature. Fe0.88Si0.12 foil was loaded into a diamond anvil cell (DAC), and then liquid hydrogen was introduced at temperatures below 20 K. The results demonstrate that the octahedral sites of Fe-Si-H alloys are not fully occupied by hydrogen unlike the case of FeH and as a consequence Fe0.88Si0.12H0.8 is formed under hydrogen-saturated condition. The compressibility of hcp Fe0.88Si0.12H0.8 is similar to that of pure iron. Assuming that liquid and solid alloys have identical density and ideal solution of hydorogen and silicon in the hcp phase, we found that the observed density profile in the outer core may be reconciled with Fe0.88Si0.12H0.4. It means that the amount of hydrogen corresponding to about 90 times seawater could be in the Earth's core. This study suggests that Fe-Si-H system is a plausible chemical composition of the core.