Effect of Si on liquid Fe compressibility: Implications for sound velocity in core materials

Density of liquid Fe‐Si alloys was measured in situ up to 5 GPa‐1725 K by an X‐ray absorption technique using synchrotron radiation. Increasing the amount of silicon in liquid iron decreases the bulk incompressibility by only −0.5 GPa per 1 weight% of Si. These data confirm our previous prediction of a negligible effect of Si on liquid Fe bulk properties, prediction based on the observation of a similar local structure in liquid Fe and liquid Fe‐Si alloys. Si and S have therefore opposite effects on P‐waves velocity ( v P = ), both elements reduce the bulk density of liquid iron but only S affects its compressibility. Since compression‐wave velocities in the Earth's outer core are slightly higher than in pure liquid Fe in the same P‐T conditions, it implies that Si would correct this discrepancy while S would increase it.