In situviscometry of high-pressure melts in the Paris–Edinburgh cell: application to liquid FeS

High-pressure viscosity of liquid Fe and FeS revisited by falling sphere viscometry using ultrafast X-ray imaging

“…In contrast, later studies used an in situ X-ray radiography technique to monitor the fall of the probing spheres and reported that liquid Fe-S alloys have very low viscosities around 10 mPa s, about 3 orders of magnitude lower than those reported by LeBlanc and Secco (1996). However, the reported results from these previous in-situ studies are also scattered, covering a range of almost one order of magnitude: 2.4-23.7 mPa s for liquid Fe (Terasaki et al, 2002;Rutter et al, 2002), 3.6-17.9 mPa s for liquid FeS (Dobson et al, 2000;Perrillat et al, 2010), and 7.4-35.6 mPa s for the eutectic Fe-S liquid (Dobson et al, 2000;Terasaki et al, 2001;Urakawa et al, 2001). For example for liquid Fe, Terasaki et al (2002) reported an increase of viscosity with increasing pressure from 17.4 mPa s at 2.8 GPa and 1692°C to 23.7 mPa s at 5.4 GPa and 1820°C, and then a rapid decrease to about 6-9 mPa s at 6-7 GPa around 1900°C, respectively.…”

“…Such low-speed imaging may be sufficient for studying viscous melts such as silicates or oxides, but it is insufficient to study less viscous liquids such as liquid Fe alloys. For example, some viscosity results were based on only 2-4 images of the falling balls (Dobson et al, 2000;Terasaki et al, 2001;Urakawa et al, 2001;Perrillat et al, 2010). Such limited imaging rates make it difficult to ensure that the falling sphere has reached terminal velocity and therefore result in large uncertainties in the calculated viscosity.…”

“…It is thought that some planetary cores, including the Earth's, are mainly composed of liquid iron with certain light elements (e.g., Birch, 1964;Poirier, 1994;Stevenson, 2001;Weber et al, 2011). Efforts have been made to determine the viscosity of liquid iron-light element alloys at high pressures and high temperatures, particularly for liquid iron-sulfur alloys (LeBlanc and Secco, 1996;Dobson et al, 2000;Terasaki et al, 2001Terasaki et al, , 2002Terasaki et al, , 2006Urakawa et al, 2001;Rutter et al, 2002;Perrillat et al, 2010). The pioneering study of LeBlanc and Secco (1996) reported a high viscosity of 1.6-43.6 Â 10 3 mPa s for Fe-27 wt.% S liquid at 2-5 GPa and 1100-1300°C using the falling sphere technique by analyzing probing sphere positions in samples quenched from high-pressure and high-temperature conditions.…”

Toward comprehensive studies of liquids at high pressures and high temperatures: Combined structure, elastic wave velocity, and viscosity measurements in the Paris–Edinburgh cell

“…Structure and physical properties of liquids have been much less studied than those of crystalline materials due to experimental difficulties. Some efforts have been made to investigate structure of liquids [e.g., Tsuji et al, 1989;Mezouar et al, 2002;Shen et al, 2004;Yamada et al, 2011], physical properties such as density [e.g., Katayama et al, 1998;Shen et al, 2002;Ohtani et al, 2005], viscosity [e.g., Kushiro et al, 1976;Kanzaki et al, 1987;Dobson et al, 2000;Terasaki et al, 2001;Perrillat et al, 2010], and elastic wave velocity [e.g., Krisch et al, 2002;Decremps et al, 2009;Nishida et al, 2013]. However, these results were often based on individual techniques, and the discussions were made by comparisons with results obtained by other researchers using in different apparatus using different techniques.…”

Thermal evolution of the core with a high thermal conductivity

“…The low viscosity of the core (eg Poirier, 1988;de Wijs et al, 1998;Perrillat et al, 2010) makes convection currents very efficient at mixing all the extensive variables, and in particular entropy and composition. A good evidence of that efficiency comes from the observation of the secular variation of the magnetic field which implies a flow velocity of the order of 10 −4 m s −1 (eg.…”