HR: 0800h
AN: T41B-1182    [Abstracts]
TI: Iron-nickel-water system under high pressure and high temperature
AU: * Hirao, N
EM: hirao@ganko.tohoku.ac.jp
AF: Tohoku University, Institute of Mineralogy, Petrology, and Economic Geology, Faculty of Science, Sendai, 980-8578 Japan
AU: Ohtani, E
EM: ohtani@mail.tains.tohoku.ac.jp
AF: Tohoku University, Institute of Mineralogy, Petrology, and Economic Geology, Faculty of Science, Sendai, 980-8578 Japan
AU: Kondo, T
EM: tdskondo@mail.tains.tohoku.ac.jp
AF: Tohoku University, Institute of Mineralogy, Petrology, and Economic Geology, Faculty of Science, Sendai, 980-8578 Japan
AU: Kikegawa, T
EM: takumi.kikegawa@kek.jp
AF: High Energy Accelerator Reaserch Organization, Photon Factory, Tsukuba, 305-0801 Japan
AB: Hydrogen has been proposed as one of the light elements in the Earth's core. Information on hydrogen distribution between the mantle and core is very important because hydrogen would have profound influence on the rheological properties and phase relations of minerals and rocks and the Earth's dynamics in global scale. The behavior of water in the primordial Earth also remains unclear. Since the discovery of high solubility of hydrogen into iron at high pressure, various studies on the Fe-H and Fe-H$_{2}$O systems have been carried out. However, the Earth's core contains 5-15$%$ nickel, based on cosmochemistry arguments. In order to simulate more realistic condition for the core formation process in proto-Earth, we investigated the reaction between iron-nickel alloys, Fe$_{90}$Ni$_{10}$ and Fe$_{95}$Ni$_{5}$, and water at high pressures and high temperatures. A series of experiments were performed in the laser-heated diamond-anvil cell (LHDAC) at pressures 5 to 23 GPa and temperatures up to 1220 K with synchrotron radiation at BL13A beamline of Photon Factory (PF), High Energy Accelerator Research Organization (KEK). The reaction of iron-nickel alloys with water depends on pressure. Iron-nickel hydrides (Fe,Ni)H and iron-nickel hydroxide (Fe,Ni)(OH)$_{2}$ were formed at low pressure of 5 GPa, while iron-nickel oxide (Fe,Ni)O and iron-nickel oxyhydroxide (Fe,Ni)OOH coexisting with iron-nickel hydride (Fe,Ni)H were observed above 18 GPa. We found that the amount of hydride formed by the reaction is smaller in the iron-nickel-water system than in the iron-water system, although the hydrogen content in iron-nickel hydride is not significantly different from that in iron hydride. Our results indicate that the existence of nickel in iron tend to reduce the amount of hydrogen supplied into the Earth's core.
DE: 3924 High-pressure behavior
DE: 3954 X ray, neutron, and electron spectroscopy and diffraction
DE: 1060 Planetary geochemistry (5405, 5410, 5704, 5709, 6005, 6008)
DE: 1015 Composition of the core
SC: Tectonophysics [T]
MN: 2004 AGU Fall Meeting