Phase relations of iron determined by in-situ x-ray diffraction in an internally-heated diamond anvil cell

HR: 12:02h
AN: MR22A-09 [Abstracts]
TI: Phase relations of iron determined by in-situ x-ray diffraction in an internally-heated diamond anvil cell
AU: * Komabayashi, T
EM: komabayashi.t.aa@m.titech.ac.jp
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd., N.W., Washington DC, DC 20015, United States
AU: * Komabayashi, T
EM: komabayashi.t.aa@m.titech.ac.jp
AF: Department of Earth and Planetary Sciences, Tokyo Institute of Technology, 2-12-1 Ookayama, Meguro, Tokyo, 152-8551, Japan
AU: Fei, Y
EM: y.fei@gl.ciw.edu
AF: Geophysical Laboratory, Carnegie Institution of Washington, 5251 Broad Branch Rd., N.W., Washington DC, DC 20015, United States
AB: Iron, as the primary phase of the Earth's core has been extensively investigated for the last 50 years. However, iron phase diagram is still controversial above 20 GPa which is beyond the multianvil apparatus pressure range. The major controversial issues include the Clapeyron slope of the FCC-HCP boundary, the presence of beta phase, and the melting curve, because of the lack of in-situ pressure determination at high temperatures in a diamond anvil cell (DAC) and technical challenge to generate stable and uniform heating in the DAC. In this study, we investigated the iron phase diagram using an improved “internal-heating” technique combined with in- situ X-ray diffraction measurements. High-pressure was generated with a pair of diamond anvils with 350- μm culet, using a gasket made of a fine powder of cubic boron nitride. In the sample chamber, ground quartz was used as a pressure medium and corundum was put on the iron foil. A thin (~15-μm) iron (99.999%Fe) foil was used as a sample and a heater simultaneously. The iron foil is heated up by increasing power through a DC power supply. This technique provides more stable and uniform heating than the laser- heating technique and much higher temperature than the external-heating method. High-P-T in-situ x-ray diffraction experiments were performed at the beamline 13-IDD of Advanced Photon Source. Temperatures were measured by the spectroscopic method and pressures at high temperature were determined from existing equations of state of Fe, SiO₂, and Al₂O₃. We observed FCC-HCP transition in the pressure range from 20 to 50 GPa and constructed the phase relations of iron up to 50 GPa and 2000 K based on the data obtained by our new heating technique.
DE: 1015 Composition of the core
DE: 3611 Thermodynamics (0766, 1011, 8411)
DE: 3612 Reactions and phase equilibria (1012, 8412)
DE: 3630 Experimental mineralogy and petrology
DE: 3954 X-ray, neutron, and electron spectroscopy and diffraction
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting