Viscosity of Liquid Fe-17wt% Si at High Pressure and Temperature

In situ X-ray radiography falling-sphere experiments on liquid Fe-17wt% Si viscosity were carried out from 2 GPa to 7 GPa at APS and Spring-8 in multi-anvil apparati. Video images were recorded at speeds of up to 62 frames/sec. Both Re spheres coated with alumina and composite spheres of Pt or Re core and a mechanically prepared ruby mantle were used in the high pressure melts to avoid chemical reaction between the sample and the probing metallic spheres. The viscosity at the melting temperature was calculated from activation energy, which was determined from a combination of theoretical and experimental values of viscosity at ambient pressure. At the early stages of the compression (up to ~ 5.4 GPa), the viscosity increases but later appears to approach a constant value of 69 mPa.s in the higher pressure range. The constant relating activation energy to melting temperature, g, is 6.8 from this study. Assuming that temperature varies adiabatically in the core and melting temperature Tm at the inner core boundary is 4766 K and dTm dP = 10 K/GPa, the viscosity at the core-mantle boundary, inferred from this study, decreases to a value very close to the ambient pressure viscosity of 6 mPa.s for liquid metal.