• Pakhomova, A.
• Fiquet, G.
• Boccato, S.
• Baron, M. A.
• Morard, Guillaume
• Miozzi, F.
• Mezouar, M.
• Antonangeli, Daniele
• Garbarino, G.

Abstract

Properties of the Fe-Si and Fe-C binary systems have been shown unable to satisfy the geophysical and petrological constraints of the Earth's core (i.e. velocities, densities, melting temperature) if only Si or C were to be incorporated as light element. Recent ab initio calculations suggest on the contrary that density, compressional and shear sound velocities, as well as the Poisson's ratio of the inner core could be matched by an hcp-Fe alloy containing Si and C. The combined effect of the two elements in a ternary Fe-Si-C system has never been experimentally investigated under high pressure. We thus studied the melting curve and the phase relations of the ternary iron-silicon-carbon system by in situ X-ray diffraction at high pressures and high temperatures. Starting with a low light element content (4 at% C-3 at% Si), a stable assemblage made of hcp Fe (+Si, +C) and Fe3C is observed up to 200 GPa. Fe can incorporate both Si and C in its hexagonal structure, with the latter strongly affecting the volume and the melting temperature. While the presence of a third light element is likely necessary, we here document that the effect of C in lowering the melting temperature of Fe-Si, is large enough to possibly keep the core-mantle boundary temperature below the solidus of the mantle silicates.

Topics

• density
• impedance spectroscopy
• Carbon
• phase
• x-ray diffraction
• Silicon
• iron
• melting temperature
• Poisson's ratio