Stokes‐Einstein relation in liquid iron‐nickel alloy up to 300 GPa

Abstract

Molecular dynamic simulations were applied to investigate the Stokes‐Einstein relation (SER) and the Rosenfeld entropy scaling law (ESL) in liquid Fe0.9Ni0.1 over a sufficiently broad range of temperatures (0.70 < T/Tm < 1.85; Tm is melting temperature) and pressures (from 50 GPa to 300 GPa). Our results suggest that the SER and ESL hold well in the normal liquid region and break down in the supercooled region under high‐pressure conditions, and the deviation becomes larger with decreasing temperature. In other words, the SER can be used to calculate the viscosity of liquid Earth's outer core from the self‐diffusion coefficients of iron/nickel and the ESL can be used to predict the viscosity and diffusion coefficients of liquid Earth's outer core form its structural properties. In addition, the pressure dependence of effective diameters cannot be ignored in the course of using the SER. Moreover, ESL provides a useful, structure‐based probe for the validity of SER, while the ratio of the self‐diffusion coefficients of the components cannot be used as a probe for the validity of SER.

Viscosity of Fe‐Ni‐C Liquids up to Core Pressures and Implications for Dynamics of Planetary Cores

“…(2019) (Figure S4 in Supporting Information ). The viscosity of Fe is consistent with the previous calculation of Fe and Fe 90 Ni 10 (Cao & Wang, 2017; de Wijs et al., 1998). Our results show that the viscosity of Fe 90 Ni 10 ‐3wt.% C and Fe 90 Ni 10 ‐5wt.% C are similar at both calculated conditions, and they are ∼2 mPa·s (30%) and ∼7 mPa·s (55%) higher than the viscosity of Fe at CMB and ICB conditions (Figure 3).…”

“…In this study, we directly calculated the viscosity of Fe, Fe 90 Ni 10 -1wt.%C, Fe 90 Ni 10 -3wt.%C, and Fe 90 Ni 10 -5wt.%C at the core mantle boundary (CMB) and inner core boundary (ICB) conditions, using the method as described in Wang et al (2019) (Figure S4 in Supporting Information S1). The viscosity of Fe is consistent with the previous calculation of Fe and Fe 90 Ni 10 (Cao & Wang, 2017;de Wijs et al, 1998). Our results show that the viscosity of Fe 90 Ni 10 -3wt.% C and Fe 90 Ni 10 -5wt.% C are similar at both calculated conditions, and they are ∼2 mPa•s (30%) and ∼7 mPa•s (55%) higher than the viscosity of Fe at CMB and ICB conditions (Figure 3).…”

“…The viscosities from core mantle boundary (4050 K) to inner core boundary (5530 K) conditions increase slightly for all Fe‐Ni‐C species (light red band) and remain similar for Fe liquid. The gray band shows the calculated viscosity of Fe 90 Ni 10 at 50–300 GPa from melting point ( T m , 2200 K at 50 GPa and 6500 K at 300 GPa) to 1.85 times of T m (Cao & Wang, 2017). Previous results of Fe (Alfè & Gillan, 1998; de Wijs et al., 1998) and Fe‐S (Alfè & Gillan, 1998) are also plotted for comparison.…”

Ab Initio Determination on Diffusion Coefficient and Viscosity of FeNi Fluid Under Earth’s Core Condition

“…Examination of the Stokes-Einstein relation with respect to 1 𝑎𝑘 𝐵 𝑇 ⁄ . Application Stokes-Einstein relation for Fe-Ni systems [18]. Under the same pressure and constituent, both the viscosity and diffusion coefficients increase with temperature.…”

“…QMD calculation shows that the viscosity is 13 mPa s and diffusion coefficients 5 × 10 −9 m 2 s -1 at the inner-core boundary(ICB), and 12 mPa and 4 × 10 −9 m 2 s -1 at the core-mantle boundary (CMB) [17]. The viscosity is about several mPa s for MD results of FeNi fluid [18]. Though there were limitations in MD, the early report MD results claim that Ni has a negligible effect on viscosity [19].…”