Equation of state of liquid Fe‐10 wt % S: Implications for the metallic cores of planetary bodies

Abstract

The equation of state (EOS) of molten Fe‐10 wt % S was investigated by means of static high‐pressure density measurements using a newly developed variation of the sink/float technique. The method involves the use of tailored density composite spheres made of Pt or WC cores and an Al 2 O 3 (ruby/sapphire) mantle as bracketing markers for comparative density measurements of liquid Fe‐10 wt % S at pressures (P) up to 20 GPa and at temperatures (T) up to 2123 K. The results of isothermal compression data confirm the validity of extrapolating to 20 GPa an EOS for pressures up to 6 GPa obtained earlier by Sanloup et al. [2000] using an X‐ray absorption technique. The analysis of new data obtained in the 1773–2123 K interval up to 20 GPa resulted in new EOS parameters and also revealed the need for a well‐determined melt density value at 1 atm. Application of our results to the identification of composition of liquid metallic cores of Ganymede, Io, and Mars showed Fe‐10 wt % S to be a possible candidate. We used different EOS formulations to extrapolate our results to the P‐T conditions of the Earth's interior. For temperatures between 4773 K at the core‐mantle boundary and 5973 K at the inner core boundary the extrapolation made using the Vinet EOS resulted in density values closest to the density of the core suggested by the preliminary reference Earth model.