Viscosity of water measured to pressures of 6 GPa and temperatures of 300 degrees C.

Shear viscosities of fluid water have been measured to 300 degrees C and 6 GPa (60 kbar). Measurements were made in a diamond-anvil cell with a rolling-ball technique. Enskog's equation for viscosity, coupled with an ad hoc assumption that increased collision rates are due to an "excluded volume", yield excellent matches to the data at temperatures of 100 degrees C and over, without any freely variable parameter. The data overlap the pressure-temperature range in which experiments on shocked water have previously been interpreted to indicate extremely high viscosities. It is shown conclusively that viscosities in this region are very close to those at ambient temperature. Further, it is argued that explanations of high apparent viscosities which rely on the putative formation of ice behind the shock front are probably incorrect.