Equation of state and phase diagram of Fe-16Si alloy as a candidate component of Earth's core

Journal Article · Fri Jul 29 00:00:00 EDT 2016 · Earth and Planetary Science Letters

DOI:https://doi.org/10.1016/j.epsl.2012.09.022· OSTI ID:1054004

Fischer, Rebecca A; Campbell, Andrew J; Caracas, Razvan; Reaman, Daniel M; Dera, Przymyslaw; Prakapenka, Vitali B ^[1]

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1. Ecole

The outer core of the Earth contains several weight percent of one or more unknown light elements, which may include silicon. Therefore it is critical to understand the high pressure–temperature properties and behavior of an iron–silicon alloy with a geophysically relevant composition (16 wt% silicon). We experimentally determined the melting curve, subsolidus phase diagram, and equations of state of all phases of Fe–16 wt%Si to 140 GPa, finding a conversion from the D0₃ crystal structure to a B2+hcp mixture at high pressures. The melting curve implies that 3520 K is a minimum temperature for the Earth's outer core, if it consists solely of Fe–Si alloy, and that the eutectic composition in the Fe–Si system is less than 16 wt% silicon at core–mantle boundary conditions. Comparing our new equation of state to that of iron and the density of the core, we find that for an Fe–Ni–Si outer core, 11.3±1.5 wt% silicon would be required to match the core's observed density at the core–mantle boundary. We have also performed first-principles calculations of the equations of state of Fe₃Si with the D0₃ structure, hcp iron, and FeSi with the B2 structure using density-functional theory.

• Research Organization: Argonne National Lab. (ANL), Argonne, IL (United States). Advanced Photon Source (APS)
• Sponsoring Organization: NSFDOE - BASIC ENERGY SCIENCES
• OSTI ID: 1054004
• Journal Information: Earth and Planetary Science Letters, Vol. 357-358; ISSN 0012-821X
• Country of Publication: United States
• Language: ENGLISH