Thermoelastic properties of liquid Fe‐C revealed by sound velocity and density measurements at high pressure. Issue 11 (22nd November 2016)

• Record Type: Journal Article
• Authors: Shimoyama, Yuta; Terasaki, Hidenori; Urakawa, Satoru; Takubo, Yusaku; Kuwabara, Soma; Kishimoto, Shunpachi; Watanuki, Tetsu; Machida, Akihiko; Katayama, Yoshinori; Kondo, Tadashi
• Is Part Of: Journal of geophysical research. Volume 121:Issue 11(2016:Nov.)
• Page Start: 7984
• Page End: 7995
• Publication Date: 2016-11-22
• Subjects: high pressure -- liquid Fe‐C -- density -- sound velocity; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1002/2016JB012968
• Languages: English
• ISSNs: 2169-9313

Abstract

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 K 0, 1700 K = 83.9 GPa, d KT /d P = 5.9(2), and d KT / d T = −0.0638 GPa/K. The addition of carbon did not affect the isothermal bulk modulus ( KT ) of liquid Fe, but it decreased the d K/ d T 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/cm 3 ), 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. Key Points: We developed simultaneous density sound velocity measurements of liquid Fe‐alloy to determine accurate elastic properties of liquids We precisely obtained elastic properties, such as bulk modulus and its pressure and temperature derivatives, of liquid Fe‐C We found that these thermoelastic properties can explain differences in dVP/dT of Fe‐C, Fe, and Fe‐S liquids