Sound velocity measurements of liquid Fe–light-element alloys under high pressure based on inelastic X-ray scattering measurements

Monday, 15 December 2014: 11:20 AM
Yoichi Nakajima1, Saori Imada2, Tetsuya Komabayashi3, Haruka Ozawa4, Shigehiko Tateno5, Yasuhiro Kuwayama6, Satoshi Tsutsui7, Hiroshi Uchiyama7, Daisuke Ishikawa7, Alfred Q.R. Baron1,7 and Kei Hirose5, (1)RIKEN SPring-8 Center, Hyogo, Japan, (2)Tokyo Institute of Technology, Tokyo, Japan, (3)University of Edinburgh, Edinburgh, EH9, United Kingdom, (4)Institute for Research on Earth Evolution, Japan Agency for Marine-Earth Science and Technology, Kanagawa, Japan, (5)Tokyo Institute of Technology, Earth-Life Science Institute, Tokyo, Japan, (6)Ehime University, Ehime, Japan, (7)Japan Synchrotron Radiation Research Institute, Hyogo, Japan
The liquid outer core of the Earth consists predominantly of iron with 10 wt.% lighter elements, such as hydrogen, carbon, oxygen, silicon, and sulfur. Other terrestrial planets such as Mars, Mercury and Venus are also similar to the Earth in that they have a central metallic core, which are considered to be at least partially molten. The popular models for those planetary cores also favor the existence of lighter elements. The nature of the light elements is important for understanding the core formation processes and the present core structure and dynamics in terrestrial planets, which are still not well understood. The seismic wave speed is the primary information on the Earth’s core. The sound velocity of liquid Fe–light-element alloys is therefore key to constrain the light component in the Earth’s core and will be referenced for the future survey of other planets. Recently we have developed the techniques for inelastic X-ray scattering (IXS) measurement combined with diamond-anvil cell (DAC) experiments at the SPring-8 synchrotron facility, in order to investigate the sound velocities of liquid Fe–light-element alloys under high pressure and high temperature. Recently we have succeeded in determining sound velocities of liquid Fe-C and Fe-Ni-S alloys to about 40 GPa using both externally-heated and laser-heated DACs, which corresponds to the pressures of Martian and Mercurian cores. We will present our recent development of IXS measurements of liquid iron alloys and discuss the effects of carbon and sulfur on the sound velocity of planetary liquid cores.