Thermal equation of state of iron and Fe0.91Si0.09 |
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Authors: | J Zhang F Guyot |
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Institution: | (1) ChiPR and Department of Geosciences, State University of New York at Stony Brook, Stony Brook, NY 11794, USA Fax: +1-516-632-8140; e-mail: zhang@sbmp04.ess.sunysb.edu, US;(2) Laboratoire de Mineralogie-Cristallographie and IPGP, Tour 16, Case 115, 4 Place Jussieu, F-75252 Paris Cedex 05, France, FR |
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Abstract: | We have carried out an in situ synchrotron X-ray diffraction study on iron and an iron-silicon alloy Fe0.91Si0.09 at simultaneously high pressure and temperature. Unit-cell volumes, measured up to 8.9 GPa and 773 K on the bcc phases of
iron and Fe0.91Si0.09, are analyzed using the Birch-Murnaghan equation of state and thermal pressure approach of Anderson. Equation of state parameters
on iron are found to be in agreement with results of previous studies. For both iron and Fe0.91Si0.09, thermal pressures show strong dependence on volume; the (∂KT/∂T)V values are considerably larger than those previously reported for other solids. The present results, in combination with
our previous results on ɛ-FeSi, suggest a small dependency of the room-temperature bulk modulus upon the silicon content,
less than 0.3 GPa for 1 wt.% silicon. We also find that substitution of silicon in iron would not appreciably change the thermoelastic
properties of iron-rich Fe−Si alloys. If this behavior persists over large pressure and temperature ranges, the relative density
contrast between iron and iron-rich Fe−Si alloys at conditions of the outer core of the Earth could be close to that measured
at ambient conditions, i.e., 0.6% for 1 wt.% Si.
Received: 13 January 1998 / Revised, accepted: 8 May 1998 |
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Keywords: | Iron Fe Si alloy X-ray diffraction Equation of state Thermoelasticity |
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