HR: 17:45h
AN: V32G-08    [PDF]
TI: Accurate Determination of Fluid Thermodynamics at High Pressure and Temperature
AU: * Brown, J M
EM: brown@ess.washington.edu
AF: Department of Earth and Space Sciences, University of Washington, Box 351310, Seattle, WA 98195 United States
AU: Abramson, E H
EM: evan@ess.washington.edu
AF: Department of Earth and Space Sciences, University of Washington, Box 351310, Seattle, WA 98195 United States
AB: Prerequisite for geochemical modeling of deep earth systems are accurate thermodynamic properties of all constituents at elevated pressures and temperatures. Unfortunately, fundamental data above a few tenths of GPa are sparse and do not uniformly satisfy all thermodynamic cross relationships. We present an experimental strategy for the determination of an internally consistent and complete equation of state for fluids at high pressure. Sound velocities measured on a grid of pressure-temperature points can be recursively integrated to delineate density, heat capacity, thermal expansivity, energy, and all associated uncertainties. Using impulsive stimulated scattering to measure velocities of fluids in an externally heated diamond anvil cell, we have extended equations of state for several fluids into previously unexplored regimes of pressure and temperature. Properties of water have now been fully explored to 6 GPa and 673 K. The equation of state for water as recommended by the International Association for the Properties of Water and Steam (IAPWS) diverges less from experiment than other commonly used equations of state. However, even this formula predicts velocities that deviate from the highest-pressure measurements by almost 20 times the estimated experimental uncertainty. Uncertainty in densities range from 0.1% at 1 GPa (the IAPWS estimate) to 0.3% at 6 GPa (a regime formerly of prediction without associated uncertainty estimates). Heat capacities and thermal expansion have uncertainty of no more than a few percent. Hugoniot data are correctly predicted by a modest extrapolation of the new equation of state. Re-interpreted densities from inclusion studies to 3 GPa and 1873 K are also consistent with the new equation of state.
DE: 3630 Experimental mineralogy and petrology
DE: 3919 Equations of state
DE: 3939 Physical thermodynamics
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting