In situ measurement of viscosity of liquids in the Fe-FeS system at high pressures and temperatures

The viscosity of liquid FeS and Fe-FeS eutectic was measured at pressures b etween 0.5 and 5.0 GPa using a synchrotron-based falling sphere technique. We obtain viscosities of 2 x 10(-2) to 4 x 10(-3) Pa-s in FeS at 1450 to 17 00 degreesC and 2 x 10(-2) to 8 x 10(-3) Pa-s in Fe-S-eut at 1150 to 1380 d egreesC. These results are consistent with recent viscosity measurements in Fe-S-eut at 5 to 7 GPa (Urakawa, in preparation), measured diffusivities ( Dobson 2000) and ab initio simulated viscosity (Vocadlo et al. 2000). The r esults are also similar to the values for pure iron at low pressure (Shimoj i and Itami 1986). A systematic increase in viscosity and activation energy is seen with increasing sulfur content. Interpolation between the data pre sented yields a viscosity of 1.4 x 10(-2) Pa-s for an outer core compositio n with similar to 10 wt% S at the melting temperature. There is good eviden ce of homologous behavior for Fe-S liquids which implies that the liquid al loy at the inner core boundary may have a similar viscosity.