2:45 PM - 3:00 PM
[R3-12] Sound velocity of B2-FeNiSi alloy at high pressure and high temperature and constitution of the Earth’s inner core
Keywords:Sound velocity, B2-FeNiSi alloy, High pressure and high temperature, Inner core
Elastic properties of an ordered derivative of the body-cantered cubic (B2) structure of Fe-7wt% Ni-15wt% Si (Fe0.67Ni0.06Si0.27) alloy have been investigated by combining high-resolution inelastic X-ray scattering and powder X-ray diffraction in diamond anvil cells up to 130 GPa and 2300 K. The density (ρ)-compressional wave velocity (VP) relation of this phase shows a weak or almost negligible temperature dependence, similar to that observed for the body-centered cubic phase of pure iron (Shibazaki et al, 2016) and the B20 phase of iron-silicon alloys (Whitaker et al., 2009). The ρ, VP and shear wave velocity (VS) were extrapolated to the inner core conditions and compared with the PREM (preliminary reference Earth model) inner core (Dziewonski and Anderson, 1981). The phase relation of the Fe-Ni-Si system revealed that B2-Fe-7wt% Ni-15wt% Si alloy coexists with hexagonal close-packed (hcp) Fe-Ni alloys with negligible amount of silicon (Ikuta et al., 2021). The VP and VS of the two-phase mixture of B2 and hcp phases under the inner core conditions show slightly higher VP and VS compared to the PREM inner core. The two-phase mixture with the addition of a small amount of sulfur could potentially explain the properties of the PREM inner core.