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Title: Thermal Expansion of Iron-Rich Alloys and Implications for the Earth's Core

Abstract

Understanding the thermal-chemical state of the Earth's core requires knowledge of the thermal expansion of iron-rich alloys at megabar pressures and high temperatures. Our survey of literature revealed a significant lack of such data. We have determined the unit-cell parameters of the iron-sulfur compound Fe{sub 3}S by using synchrotron x-ray diffraction techniques and externally heated diamond-anvil cells at pressures up to 42.5 GPa and temperatures up to 900 K. The zero-pressure thermal expansivity of Fe{sub 3}S is determined in the form {alpha} = a{sub 1} + a{sub 2} T, where a{sub 1} = 3.0 {+-} 1.3 x 10{sup -5} K{sup -1} and {alpha}{sub 2} = 2.8 {+-} 1.5 x 10{sup -8} K{sup -2}. The temperature dependence of isothermal bulk modulus ({partial_derivative}K{sub T,0}/{partial_derivative}T){sub P} is estimated at -3.75 {+-} 1.80 x 10{sup -2} GPa K{sup -1}. Our data at 42.5 GPa and 900 K suggest that {approx}2.1 at. % (1.2 wt. %) sulfur produces 1% density deficit in iron. We have also carried out energy-dispersive x-ray diffraction measurements on pure iron and Fe{sub 0.864}Si{sub 0.136} alloy samples that were placed symmetrically in the same multianvil cell assemblies, using the SPring-8 synchrotron facility in Japan. Based on direct comparison of unit cellmore » volumes under presumably identical pressures and temperatures, our data suggest that at most 3.2 at. % (1.6 wt. %) silicon is needed to produce 1% density deficit with respect to pure iron.« less

Authors:
; ; ;
Publication Date:
Research Org.:
Brookhaven National Laboratory (BNL) National Synchrotron Light Source
Sponsoring Org.:
Doe - Office Of Science
OSTI Identifier:
930441
Report Number(s):
BNL-81186-2008-JA
Journal ID: ISSN 0027-8424; PNASA6; TRN: US0901390
DOE Contract Number:  
DE-AC02-98CH10886
Resource Type:
Journal Article
Resource Relation:
Journal Name: Proceedings of the National Academy of Sciences of the USA; Journal Volume: 104; Journal Issue: 22
Country of Publication:
United States
Language:
English
Subject:
43 PARTICLE ACCELERATORS; ALLOYS; DIAMONDS; EARTH CORE; IRON; JAPAN; PRESSURE RANGE GIGA PA; SILICON; SULFUR; SYNCHROTRON RADIATION; SYNCHROTRON RADIATION SOURCES; TEMPERATURE DEPENDENCE; TEMPERATURE RANGE 0400-1000 K; THERMAL EXPANSION; X-RAY DIFFRACTION; national synchrotron light source

Citation Formats

Chen,B., Gao, L., Funakoshi, K., and Li, J.. Thermal Expansion of Iron-Rich Alloys and Implications for the Earth's Core. United States: N. p., 2007. Web. doi:10.1073/pnas.0610474104.
Chen,B., Gao, L., Funakoshi, K., & Li, J.. Thermal Expansion of Iron-Rich Alloys and Implications for the Earth's Core. United States. doi:10.1073/pnas.0610474104.
Chen,B., Gao, L., Funakoshi, K., and Li, J.. Mon . "Thermal Expansion of Iron-Rich Alloys and Implications for the Earth's Core". United States. doi:10.1073/pnas.0610474104.
@article{osti_930441,
title = {Thermal Expansion of Iron-Rich Alloys and Implications for the Earth's Core},
author = {Chen,B. and Gao, L. and Funakoshi, K. and Li, J.},
abstractNote = {Understanding the thermal-chemical state of the Earth's core requires knowledge of the thermal expansion of iron-rich alloys at megabar pressures and high temperatures. Our survey of literature revealed a significant lack of such data. We have determined the unit-cell parameters of the iron-sulfur compound Fe{sub 3}S by using synchrotron x-ray diffraction techniques and externally heated diamond-anvil cells at pressures up to 42.5 GPa and temperatures up to 900 K. The zero-pressure thermal expansivity of Fe{sub 3}S is determined in the form {alpha} = a{sub 1} + a{sub 2} T, where a{sub 1} = 3.0 {+-} 1.3 x 10{sup -5} K{sup -1} and {alpha}{sub 2} = 2.8 {+-} 1.5 x 10{sup -8} K{sup -2}. The temperature dependence of isothermal bulk modulus ({partial_derivative}K{sub T,0}/{partial_derivative}T){sub P} is estimated at -3.75 {+-} 1.80 x 10{sup -2} GPa K{sup -1}. Our data at 42.5 GPa and 900 K suggest that {approx}2.1 at. % (1.2 wt. %) sulfur produces 1% density deficit in iron. We have also carried out energy-dispersive x-ray diffraction measurements on pure iron and Fe{sub 0.864}Si{sub 0.136} alloy samples that were placed symmetrically in the same multianvil cell assemblies, using the SPring-8 synchrotron facility in Japan. Based on direct comparison of unit cell volumes under presumably identical pressures and temperatures, our data suggest that at most 3.2 at. % (1.6 wt. %) silicon is needed to produce 1% density deficit with respect to pure iron.},
doi = {10.1073/pnas.0610474104},
journal = {Proceedings of the National Academy of Sciences of the USA},
number = 22,
volume = 104,
place = {United States},
year = {Mon Jan 01 00:00:00 EST 2007},
month = {Mon Jan 01 00:00:00 EST 2007}
}