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Sound wave velocities of Fe (sub 5) Si at high-pressure and high-temperature conditions; implications to lunar and planetary cores

Deng Liwei, Yoshio Kono and Shen Guoyin
Sound wave velocities of Fe (sub 5) Si at high-pressure and high-temperature conditions; implications to lunar and planetary cores
American Mineralogist (February 2019) 104 (2): 291-299

Abstract

Elastic properties of Fe alloys are critical in constraining the compositions of planetary bodies by comparing to the planetary observations. The sound wave velocities and density of an Fe (sub 5) Si (9 wt% Si) alloy in body-centered cubic (bcc) structure were measured by combining an ultrasonic technique with synchrotron X-ray radiography at pressure (P) and temperature (T) conditions of 2.6-7.5 GPa and 300-1173 K, respectively. At room temperature, it is observed that adding Si to bcc-Fe increases the compressional wave velocity (V (sub P) ) but decreases the shear wave velocity (V (sub S) ). At high temperatures, we observed a pronounced effect of pressure on the V (sub S) -T relations in the Fe (sub 5) Si alloy. The V (sub P) -density (rho ) relationship of the Fe (sub 5) Si alloy is found to follow the Birch's law in the P-T range of this study, whereas the V (sub S) -rho relation exhibits complex behavior. Implications of these results to the lunar core and the Mercurian core are discussed. Our results imply that adding Si to a pure Fe lunar core would be invisible in terms of V (sub P) , but exhibit a decreased V (sub S) . Including Si in a sulfur-rich lunar core would display an increased V (sub P) and a decreased rho . Our density and sound wave velocity model provide lower and upper limit for a Si-bearing lunar core if 1-3 wt% Si content of enstatite chondrite is taken as compositional analog. A Si-rich (>9 wt%) Mercurian core model is derived to satisfy newly observed moment of inertia values by Messenger spacecraft.


ISSN: 0003-004X
EISSN: 1945-3027
Coden: AMMIAY
Serial Title: American Mineralogist
Serial Volume: 104
Serial Issue: 2
Title: Sound wave velocities of Fe (sub 5) Si at high-pressure and high-temperature conditions; implications to lunar and planetary cores
Affiliation: Chinese Academy of Sciences, Institute of Geology and Geophysics, Beijing, China
Pages: 291-299
Published: 201902
Text Language: English
Publisher: Mineralogical Society of America, Washington, DC, United States
References: 64
Accession Number: 2019-044213
Categories: Geophysics of minerals and rocks
Document Type: Serial
Bibliographic Level: Analytic
Illustration Description: illus. incl. 1 table
Secondary Affiliation: University of Chinese Academy of Sciences, CHN, ChinaCarnegie Institution of Washington, USA, United States
Country of Publication: United States
Secondary Affiliation: GeoRef, Copyright 2019, American Geosciences Institute. Abstract, copyright, Mineralogical Society of America. Reference includes data from GeoScienceWorld, Alexandria, VA, United States
Update Code: 201911
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