Publication Date:
2019
Description:
〈span〉〈div〉Abstract〈/div〉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〈/sub〉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 (〈span〉P〈/span〉) and temperature (〈span〉T〈/span〉) 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 (ν〈sub〉P〈/sub〉) but decreases the shear wave velocity (ν〈sub〉S〈/sub〉). At high temperatures, we observed a pronounced effect of pressure on the ν〈sub〉S〈/sub〉-〈span〉T〈/span〉 relations in the Fe〈sub〉5〈/sub〉Si alloy. The ν〈sub〉P〈/sub〉-density (ρ) relationship of the Fe〈sub〉5〈/sub〉Si alloy is found to follow the Birch's law in the 〈span〉P-T〈/span〉 range of this study, whereas the ν〈sub〉S〈/sub〉-ρ 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 ν〈sub〉P〈/sub〉, but exhibit a decreased ν〈sub〉S〈/sub〉. Including Si in a sulfur-rich lunar core would display an increased ν〈sub〉P〈/sub〉 and a decreased ρ. 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.〈/span〉
Print ISSN:
0003-004X
Electronic ISSN:
1945-3027
Topics:
Geosciences
,
Physics
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