16:30 〜 16:45
[SIT17-05] Sound velocity measurements of liquid Fe-N up to 100 GPa
キーワード：地球コア、液体Fe-N、音速、非弾性X線散乱、高圧
The Earth’s liquid outer core consists of iron alloy with ~5 wt.% nickel and ~10 wt.% lighter elements [1]. Nitrogen is one of the candidates for the core light elements. The Earth’s atmosphere and silicate mantle is depleted in nitrogen relative to carbonaceous chondrites, which indicates that a large portion of the nitrogen in bulk earth can be stored in the core [2,3]. To examine the possibility of nitrogen in the core, it is utilized to compare the sound velocity of liquid Fe-N alloy under high-pressure and –temperature conditions relevant to the core conditions with seismological observations. We have determined the longitudinal (P-wave) velocity of liquid Fe-N alloy up to 99 GPa and 2600 K based on the inelastic X-ray scattering (IXS) measurements in a laser-heated diamond-anvil cell (LH-DAC).
We carried out IXS measurements at the RIKEN Quantum NanoDynamics beamline BL43LXU of SPring-8 [4]. A Fe80N20 (Fe4N) foil was used as the starting specimen and single-crystal Al2O3 discs were used as the thermal- and chemical-insulator. The liquid state of the sample was confirmed before and after each IXS measurement based on X-ray diffraction measurements. The IXS spectra were collected in a momentum transfer range of 3-5.7 nm-1 with an energy resolution of ~2.8 meV at 17.94 keV. The P-wave velocity of liquid Fe80N20 was determined from the dispersion relation of the longitudinal acoustic phonon mode of the liquid. We constructed an equation of state (EoS) for liquid Fe80N20 from the pressure and velocity data. Compared with pure Fe [5], the P-wave velocity of liquid Fe80N20 is faster by ~10% in the present experimental conditions. By extrapolating the present results to the Earth’s outer core conditions with the present EoS and then comparing with seismological observations, we found that the upper limit of nitrogen is ~3.8 wt% in the outer core.
References
[1] Stevenson, Science 214, 611-619 (1981).
[2] Marty, Earth Planet. Sci. Lett. 313-314, 56-66 (2012).
[3] Li et al., Earth Planet. Sci. Lett. 377-378, 311-323 (2013).
[4] Baron, SPring-8 Inf. Newsl. 15(1), 14-19 (2010).
[5] Kuwayama et al. Phys. Rev. Lett. 124(16), 165701 (2020).
We carried out IXS measurements at the RIKEN Quantum NanoDynamics beamline BL43LXU of SPring-8 [4]. A Fe80N20 (Fe4N) foil was used as the starting specimen and single-crystal Al2O3 discs were used as the thermal- and chemical-insulator. The liquid state of the sample was confirmed before and after each IXS measurement based on X-ray diffraction measurements. The IXS spectra were collected in a momentum transfer range of 3-5.7 nm-1 with an energy resolution of ~2.8 meV at 17.94 keV. The P-wave velocity of liquid Fe80N20 was determined from the dispersion relation of the longitudinal acoustic phonon mode of the liquid. We constructed an equation of state (EoS) for liquid Fe80N20 from the pressure and velocity data. Compared with pure Fe [5], the P-wave velocity of liquid Fe80N20 is faster by ~10% in the present experimental conditions. By extrapolating the present results to the Earth’s outer core conditions with the present EoS and then comparing with seismological observations, we found that the upper limit of nitrogen is ~3.8 wt% in the outer core.
References
[1] Stevenson, Science 214, 611-619 (1981).
[2] Marty, Earth Planet. Sci. Lett. 313-314, 56-66 (2012).
[3] Li et al., Earth Planet. Sci. Lett. 377-378, 311-323 (2013).
[4] Baron, SPring-8 Inf. Newsl. 15(1), 14-19 (2010).
[5] Kuwayama et al. Phys. Rev. Lett. 124(16), 165701 (2020).