Department of Physics and Astronomy

Permanent link for this collectionhttps://hdl.handle.net/2022/22354

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Browsing Department of Physics and Astronomy by Subject "Earth (Planet) -- Core"

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    Phase relations of Fe-Si alloy in Earth’s core
    (Wiley, 2009) Lin, Jung-Fu; Scott, Henry P.; Fischer, Rebecca A.; Chang, Yun-Yuan; Kantor, Innokenty; Prakapenka, Vitali B.
    Phase relations of an Fe0.85Si0.15 alloy were investigated up to 240 GPa and 3000 K using in situ X-ray diffraction in a laser-heated diamond anvil cell. An alloy of this composition as starting material is found to result in a stabilized mixture of Si-rich bcc and Si-poor hcp Fe-Si phases up to at least 150 GPa and 3000 K, whereas only hcp-Fe0.85Si0.15 is found to be stable between approximately 170 GPa and 240 GPa at high temperatures. Our extended results indicate that Fe0.85Si0.15 alloy is likely to have the hcp structure in the inner core, instead of the previously proposed mixture of hcp and bcc phases. Due to the volumetric dominance of the hcp phase in the hcp + bcc coexistence region close to the outer-core conditions, the dense closest-packed Fe-Si liquid is more relevant to understanding the properties of the outer core.
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    Pressure-induced magnetic transition and sound velocities of Fe3C: Implications for carbon in the Earth’s inner core
    (Wiley, 2008) Gao, Lili, 1984-; Scott, Henry P.
    We have carried out nuclear resonant scattering measurements on 57Fe-enriched Fe3C between 1 bar and 50 GPa at 300 K. Synchrotron Mo¨ssbauer spectra reveal a pressure-induced magnetic transition in Fe3C between 4.3 and 6.5 GPa. On the basis of our nuclear resonant inelastic X-ray scattering spectra and existing equation-of-state data, we have derived the compressional wave velocity VP and shear wave velocity VS for the high-pressure nonmagnetic phase, which can be expressed as functions of density (r): VP(km/s) = -3.99 + 1.29r(g/cm3) and VS(km/s) = 1.45 + 0.24r(g/cm3). The addition of carbon to iron-nickel alloy brings density, VP and VS closer to seismic observations, supporting carbon as a principal light element in the Earth’s inner core.