Abstract
We observed a direct reaction of metallic iron with water to form iron hydride and iron oxide, 3Fe + H2O–>2FeH x + FeO, at pressures from 6 GPa to 84 GPa and temperatures above 1,000 K in diamond anvil cell (DAC). Iron hydride is dhcpFeH x or γ-FeH x , and iron oxide has the rhombohedral or B1 structure at pressures at least up to 37 GPa. The formation of an assembly composed of dhcpFeH x and FeO with the B8 structure was observed at 84 GPa. In primordial Earth, water formed by dehydration of the low temperature primitive materials reacts with metallic iron in the high temperature component to form iron hydride FeH x and iron oxide FeO. The former would be incorporated in the iron forming the core. Thus hydrogen could be an important element of the Earth’s core. This reaction would be essential for transport of hydrogen into the core in the accretion stage of the Earth.
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Acknowledgments
In situ X-ray diffraction was conducted at the beamlines BL13A and BL18C of the Photon Factory. We thank T. Yagi for his help and encouragement during this work. We also thank two anonymous reviewers and S. Saxena for constructive review to improve the manuscript. This work was partially supported by the Grant-in-aid of the Scientific Research of Priority Area B (No. 12126201) and Scientific Research S (No.14102009) of the Ministry of Education, Science, Culture, Sport, and Technology of the Japanese Government to EO. X-ray diffraction experiments were conducted under the approval of the Photon Factory Program Committee (Proposed numbers: 01G059 and 02G055).
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Ohtani, E., Hirao, N., Kondo, T. et al. Iron-water reaction at high pressure and temperature, and hydrogen transport into the core. Phys Chem Minerals 32, 77–82 (2005). https://doi.org/10.1007/s00269-004-0443-6
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DOI: https://doi.org/10.1007/s00269-004-0443-6