11:00 〜 13:00
[SIT17-P04] Toward sound velocity measurement of liquid Fe-H under high-pressure conditions
キーワード：惑星コア、液体Fe-H、音速、高圧
Hydrogen is a candidate of the light elements in the Earth’s outer core. Recent hydrogen partitioning between liquid Fe and silicate melts under the pressure-temperature conditions during core formation processes suggested that a large amount of hydrogen could have been incorporated into the core-forming metal and may still exist in the present core [1]. Theoretical calculations revealed that a Fe-H liquid could account for sound velocity and liquid outer core density [2]. Though many experimental studies on the velocity and density of solid Fe-H phases under high pressures have been reported (e.g., [3-6]), these elastic properties of the liquid have not been measured so far. This is due to the difficulty in measuring liquid Fe-H. Here, we challenge to measure the P-wave velocity of liquid Fe-H under high pressures using inelastic X-ray scattering (IXS) and a laser-heated diamond-anvil cell (LH-DAC).
We carried out IXS and X-ray diffraction (XRD) measurements at the RIKEN Quantum NanoDynamics beamline BL43LXU of SPring-8 [7]. Following previous studies [6,8], we tried to synthesize a Fe-H sample by the chemical reaction between Fe and paraffin upon laser-heating at high pressure. A foil of Fe was sandwiched between paraffin discs that act as a hydrogen source, which was loaded in LH-DAC. A layer of KCl or NaCl was put between paraffin and diamond anvil to reduce the reaction of hydrogen with anvils, while some experiments were performed without such a chemical insulator. The hydrogenation of a Fe foil was judged from X-ray diffraction patterns from the sample upon heating.
We carried out six runs in total to synthesize Fe-H samples. First, we compressed the sample to 50-70 GPa, and then heated it to ~1600-1700 K, following previous studies [6,8]. We observed fcc-FeHx in four runs and only carbides in the others. In a run, diamond anvils were broken upon further heating to melt the FeHx sample. We succeeded in melting three FeHx samples and measuring the IXS spectra of two samples at 55 and 70 GPa. However, the melting temperatures judged from the XRD patterns were somewhat higher by ~300-600 K than FeHx [9], which might be due to the hydrogen exsolution from the FeHx sample just before or after the sample melting. We also measured the synthesized fcc-FeHx at 300 K in a pressure range of 20 to 60 GPa to compare with liquid data. We are carefully analyzing the data set now. We will present more details and discuss the results in the meeting.
References:
[1] Tagawa et al., Nat. Commun. 12(1), 1-8 (2021).
[2] Umemoto and Hirose, Geophys. Res. Lett. 42, 7513 (2015).
[3] Badding et al., Science 253, 421-424 (1991)
[4] Mao et al., Geophys. Res. Lett. 31, L15618 (2004
[5] Narygina et al., Earth Planet. Sci. Lett 307, 409-414 (2011).
[6] Shibazaki et al., Earth Planet. Sci. Lett 313, 79-74 (2012).
[7] Baron, SPring-8 Inf. Newsl. 15, 14-19 (2010).
[8] Ohta et al., C. R. Geoscience. 351, 147-153 (2019).
[9] Sakamaki et al., Phys. Earth Planet. Inter. 174, 192-201 (2009).
We carried out IXS and X-ray diffraction (XRD) measurements at the RIKEN Quantum NanoDynamics beamline BL43LXU of SPring-8 [7]. Following previous studies [6,8], we tried to synthesize a Fe-H sample by the chemical reaction between Fe and paraffin upon laser-heating at high pressure. A foil of Fe was sandwiched between paraffin discs that act as a hydrogen source, which was loaded in LH-DAC. A layer of KCl or NaCl was put between paraffin and diamond anvil to reduce the reaction of hydrogen with anvils, while some experiments were performed without such a chemical insulator. The hydrogenation of a Fe foil was judged from X-ray diffraction patterns from the sample upon heating.
We carried out six runs in total to synthesize Fe-H samples. First, we compressed the sample to 50-70 GPa, and then heated it to ~1600-1700 K, following previous studies [6,8]. We observed fcc-FeHx in four runs and only carbides in the others. In a run, diamond anvils were broken upon further heating to melt the FeHx sample. We succeeded in melting three FeHx samples and measuring the IXS spectra of two samples at 55 and 70 GPa. However, the melting temperatures judged from the XRD patterns were somewhat higher by ~300-600 K than FeHx [9], which might be due to the hydrogen exsolution from the FeHx sample just before or after the sample melting. We also measured the synthesized fcc-FeHx at 300 K in a pressure range of 20 to 60 GPa to compare with liquid data. We are carefully analyzing the data set now. We will present more details and discuss the results in the meeting.
References:
[1] Tagawa et al., Nat. Commun. 12(1), 1-8 (2021).
[2] Umemoto and Hirose, Geophys. Res. Lett. 42, 7513 (2015).
[3] Badding et al., Science 253, 421-424 (1991)
[4] Mao et al., Geophys. Res. Lett. 31, L15618 (2004
[5] Narygina et al., Earth Planet. Sci. Lett 307, 409-414 (2011).
[6] Shibazaki et al., Earth Planet. Sci. Lett 313, 79-74 (2012).
[7] Baron, SPring-8 Inf. Newsl. 15, 14-19 (2010).
[8] Ohta et al., C. R. Geoscience. 351, 147-153 (2019).
[9] Sakamaki et al., Phys. Earth Planet. Inter. 174, 192-201 (2009).