Thermoelastic properties of liquid Fe-C revealed by sound velocity and density measurements at high pressure

Yuta Shimoyama, Hidenori Terasaki, Satoru Urakawa, Yusaku Takubo, Soma Kuwabara, Shunpachi Kishimoto, Tetsu Watanuki, Akihiko Machida, Yoshinori Katayama, Tadashi Kondo

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Abstract

Carbon is one of the possible light elements in the cores of the terrestrial planets. The P wave velocity (VP) and density (ρ) are important factors for estimating the chemical composition and physical properties of the core. We simultaneously measured the VP and ρ of Fe-3.5 wt % C up to 3.4 GPa and 1850 K by using ultrasonic pulse-echo method and X-ray absorption methods. The VP of liquid Fe-3.5 wt % C decreased linearly with increasing temperature at constant pressure. The addition of carbon decreased the VP of liquid Fe by about 2% at 3 GPa and 1700 K and decreased the Fe density by about 2% at 2 GPa and 1700 K. The bulk modulus of liquid Fe-C and its pressure (P) and temperature (T) effects were precisely determined from directly measured ρ and VP data to be K0,1700 K = 83.9 GPa, dKT/dP = 5.9(2), and dKT/dT = −0.063 GPa/K. The addition of carbon did not affect the isothermal bulk modulus (KT) of liquid Fe, but it decreased the dK/dT of liquid Fe. In the ρ-VP relationship, VP increases linearly with ρ and can be approximated as VP (m/s) = −6786(506) + 1537(71) × ρ (g/cm3), suggesting that Birch's law is valid for liquid Fe-C at the present P-T conditions. Our results imply that at the conditions of the lunar core, the elastic properties of an Fe-C core are more affected by temperature than those of Fe-S core.

Original languageEnglish
Pages (from-to)7984-7995
Number of pages12
JournalJournal of Geophysical Research: Solid Earth
Volume121
Issue number11
DOIs
Publication statusPublished - Nov 1 2016

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Keywords

  • density
  • high pressure
  • liquid Fe-C
  • sound velocity

ASJC Scopus subject areas

  • Geophysics
  • Geochemistry and Petrology
  • Earth and Planetary Sciences (miscellaneous)
  • Space and Planetary Science

Cite this

Shimoyama, Y., Terasaki, H., Urakawa, S., Takubo, Y., Kuwabara, S., Kishimoto, S., Watanuki, T., Machida, A., Katayama, Y., & Kondo, T. (2016). Thermoelastic properties of liquid Fe-C revealed by sound velocity and density measurements at high pressure. Journal of Geophysical Research: Solid Earth, 121(11), 7984-7995. https://doi.org/10.1002/2016JB012968