Viscosity of planetary fluids and the amorphization of crystals at high pressure.

摘要

Transport properties of solids and fluids change by orders of magnitude as a function of different pressure and temperature. Such properties in large part dictate the mass and heat transport in planetary interiors, so their measurement at high pressures and temperatures is important. While these properties are often well constrained at room pressure, there is a dearth of measurement on fluids of all types at high pressure and temperature. The viscosity, in particular, is poorly known for many materials above 0.5 to 1.0 GPa, or at high compression (rho/rho0 ∼ 1.5-2.0).;To determine how the viscosity of different materials changes with pressure, the diamond-cell was used as a high-pressure rolling-sphere viscometer. Measurements on organic fluids reveal large changes in viscosity as a function of both temperature and pressure, with activation energies increasing significantly as the density increases. In contrast, water has only a small increase in viscosity with large increases in density, and an activation energy that remains almost constant. For both organic liquids and water, several scaling relations derived from different physical arguments fit the data equally well. This makes it difficult to reliably extrapolate viscosity data, as different models tend to diverge significantly from each other at high pressure and temperature.;X-ray diffraction measurements on the pressure-induced amorphization of tin-iodide show a small increase in transition pressure as a function of temperature. Contrary to previous interpretations, the amorphization does not need to be a two-step process, as some of the samples amorphize without converting to a second crystal phase. Large variability in the number of crystal phases, location of the glass transition pressure, and crystal volumes were observed as a function of sample loading. This may be due to the potential for extreme sensitivity of the sample to even small deviatoric stresses in the sample chamber.