Equation of State for Shocked Fe‐8.6 wt% Si up to 240 GPa and 4,670 K

Abstract

Using dynamic compression technique, the equation of state for Fe‐8.6 wt% Si was measured up to 240 GPa and 4,670 K. A least squares fit to the experimental data yields the Hugoniot parameters C0 = 4.603±0.101 km/s and λ = 1.505±0.037 with initial density ρ0=7.386±0.021 g/cm3. Based on the Hugoniot data, the calculated isothermal equation of state is consistent with static compression data when the lattice Grüneisen parameter γl =1.65(7.578/ρ) and electronic Grüneisen parameter γe=1.83. The calculated pressure‐density data at 300 K were fitted to a third‐order Birch‐Murnaghan equation of state with zero pressure the parameters K0=192.1±6.3 GPa, K0'=4.71±0.27 with fixed ρ0ε =7.578±0.050 g/cm3. Under the conditions of Earth's core, the densities of Fe‐8.6±2.0 wt% Si and Fe‐3.8±2.9 wt% Si agree with preliminary reference Earth mode (PREM) data of the outer and the inner core, respectively. These are the upper limits for Si in the core assuming Si is the only light element. Simultaneously considering the geophysical and geochemical constraints for a Si‐S‐bearing core, the outer core may contain 3.8±2.9 wt% Si and 5.6±3.0 wt% S.

Thermal conductivity of Fe-Si alloys and thermal stratification in Earth’s core

“…We should note that the concentration of Si in the core remains uncertain. While some experiments have shown that Fe alloyed with ∼9 wt % Si can satisfy the density profile of the outer core and Fe alloyed with ∼4 wt % Si for the inner core, respectively ( 37 , 40 , 41 , 51 , 52 ), other studies indicate that a dominant Si light alloying component is unable to reproduce both the density and sound velocity distribution in the outer core ( 53 , 54 ).…”

Possible Deep Structure and Composition of Venus With Respect to the Current Knowledge From Geodetic Data

“…Davies (2015), Si is partitioned between solid and liquid Fe almost equally. Therefore, we assume that the inner core contains only Si and has the same amount of Si as the liquid core, in agreement with Huang et al (2019).…”

“…Rocky planets are generally believed to have Fe-rich metallic cores containing minor contents of light elements, which may be S, O, Si, C, or H. However, there is still controversy over which light element(s) are dissolved in the Earth's core (e.g., Hirose et al, 2013). Hirose et al (2013) suggested that the liquid core contains approximately 6 wt% Si, 3 wt% O, and 1-2 wt% S. Huang et al (2019) provided evidence that the liquid core contains 5.6 ± 3.0 wt% S and 3.8 ± 2.9 wt% Si satisfying both geophysical and geochemical constraints. We assume that the light elements within the liquid core in our models are Si and S. We use three equation of state parameters, namely, ε-Fe (Fei et al, 2016), Fe-9Si (Huang et al, 2019), and Fe-12S (Huang et al, 2018), which were obtained from high-pressure experiments; the experiments are summarized in Table 2.…”

“…10.1029/2019JE006243 5 of 22 ε-Fe (Fei et al, 2016) Fe-9wt% Si (Huang et al, 2019) Fe-12wt% S (Huang et al, 2018) ρ 0 (g/cm 3 ) 8.2695 7.578 6.647…”

“…B6. We consider a 1% reduction in density from the solid phase to the liquid phase (Huang et al., 2019). In our models, it is necessary to know the solidus temperature of the core to determine the presence of a solid inner core.…”