Determination of PVTx properties of dense H2O+NaCl solutions to 5 GPa, 600 °C, and 50 wt% NaCl
Zusammenfassung der Projektergebnisse
One main goal of this project was to develop an experimental setup to measure the acoustic velocity of liquids based on Brillouin scattering and, based on these data, to determine the parameters of the equation of state of water-NaCl solutions at conditions of relevance to geologic processes in the lithosphere of the Earth and in the interior of other planetary bodies such as icy moons in the solar system. The complex development of a complete setup to perform these measurements has been completed during this project. A specifically designed customized hydrothermal diamond anvil cell (HDAC) and a combined Brillouin and Raman system have been set up and thoroughly and successfully tested over a wide range of conditions. Finally, datasets have been collected, mainly on a H2O + 15 mass% NaCl solution in a range of pressure and temperatures between ambient conditions and 2.2 GPa and 500 °C. The new datasets have been analyzed producing model densities as a function of pressure and temperature, which are consistent with the only other available study covering comparable ranges in pressure and temperature. In parallel to the velocitydensity studies, we have investigated the compositional dependence of the liquidi of H2O-NaCl mixtures by combining microthermometric and Raman spectroscopic observations at temperatures between -30 °C and 25 °C and pressures from 0.1 MPa to 1.4 GPa for NaCl contents from 5 mass% to 25 mass%. The new results show that the topology of the liquidi in the water-NaCl system is indeed strongly affected by the bulk NaCl content. At 25 mass% NaCl, the hydrohalite liquidus replaces the liquidi of ice I, ice III, and ice V, and its dP/dT slope changes from negative to positive values at ~140 MPa, which probably reflects the transition from low-density water to high-density water. The ice I liquidus shifts to lower temperatures and its negative dP/dT slope steepens with increasing NaCl content. The location of the ice I liquidi to 15 mass % NaCl has been applied to constrain the thickness of the solid icy crust above the salty subsurface ocean in Jupiter’s moon Europa to 9 km. Finally, we have detected a new solid phase formed in solutions above 10 mass% NaCl when cooled to -60 °C at moderate to high pressures between 0.2 and 1.4 GPa. Based on a combination of in situ optical observation, Raman spectroscopy and synchrotron X-ray diffraction, we constrained the pressure and temperature ranges of its presence and its transformation reaction at increasing temperature. At three bulk compositions (10.7, 15 and 24-25 mass%), we consistently detected the new phase, which has distinct optical properties, Raman bands in the O–H stretching region, and X-ray diffraction pattern. All these properties do not match those of any of the other known solid phases in the H2O-NaCl system, namely those of hydrohalite and water ice phases. At all three compositions, the unknown solid phase decomposes with increasing temperature to hydrohalite + ice VI + liquid. At a pressure between 1.1 and 1.3 GPa, the decomposition temperature increases from -15 °C to -11 °C when the NaCl content was increased from 10.7 to 24 mass%. Based on our synchrotron X-ray diffraction results, we cannot exclude that the unknown solid is indeed a mixture of more than one crystalline phase.
Projektbezogene Publikationen (Auswahl)
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(2009) Experimental determination of the H2O - 15wt% NaCl and H2O – 25% NaCl liquidi to 1.4 GPa, Eos Trans. AGU, 90 (52), 2009 Fall Meet. Suppl., Abstract V43B- 2229
Valenti P., Schmidt C.
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(2009) Experimental determination of the H2O - 15wt% NaCl liquidus to 1.4 GPa and observation of a high-pressure NaCl-hydrate, 20th European Current Research on Fluid Inclusions - ECROFI Meeting, Granada, Spain
Valenti P., Schmidt C.
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(2011) A new setup for combined Brillouin and Raman scattering to measure P-V-T-x properties of fluids in the system H2O-NaCl at high P and T in a diamond-anvil cell. Abstract MR43A-2128 presented at 2011 Fall Meeting, AGU, San Francisco, Calif., 5-9 Dec.
Valenti P., Reichmann H.J., Schmidt C., Speziale S.
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(2012) Experimental determination of H2O-NaCl liquidi to 25 mass% NaCl and 1.4 GPa: Application to the Jovian satellite Europa. Geochimica et Cosmochimica Acta, 92, 117-128
Valenti P., Bodnar R.J., Schmidt C.
