Viscosity of an Fe‐S liquid up to 1300°C and 5 GPa

Viscosity measurements of Fe 73 S 27 (wt%) liquid at pressures between 2.0 and 5.0 GPa and at temperatures in the range 1100–1300°C have been made using Stokes' method of rising spheres in conjunction with a newly developed electro‐detection technique. The viscosities range from 43.6±7.0 Pa‐s at 3.9 GPa and 1100°C to 1.6±0.5 Pa‐s at 3.0 GPa and 1300°C. These high P viscosity values are three orders of magnitude higher than the 1 atm values and are tentatively attributed to the effects of S on the size of viscous flow units. From the T and P dependences of viscosity, activation energy and volume, respectively, have been determined. Activation energy decreases with increasing P, from 405±77 kJ/mol at 2.0 GPa to 240±72 kJ/mol at 5.0 GPa, and activation volume increases with increasing T, from 1.51±0.01 cm³/mol at 1100°C to 3.61±0.19 cm³/ at 1300°C.