HR: 08:00h
AN: MR11A-01    [Abstracts]
TI: CH3OH in High-Pressure Phases of H2O: Implications for Ice-Rich Planets
AU: * Aarestad, B
EM: aareth2000@yahoo.com
AF: Department of Geology and Environmental Geosciences, Davis Hall, Northern Illinois University, DeKalb, IL 60115, United States
AU: Frank, M R
EM: mfrank@niu.edu
AF: Department of Geology and Environmental Geosciences, Davis Hall, Northern Illinois University, DeKalb, IL 60115, United States
AU: Scott, H P
EM: hpscott@iusb.edu
AF: Department of Physics and Astronomy, Indiana University, South Bend, South Bend, IN 46634, United States
AU: Maglio, S
EM: stevemaglio@gmail.com
AF: Department of Geology and Environmental Geosciences, Davis Hall, Northern Illinois University, DeKalb, IL 60115, United States
AU: Prakapenka, V
EM: prakapenka@cars.uchicago.edu
AF: Center for Advanced Radiation Sources, University of Chicago, Argonne, IL 60439, United States
AB: A significant body of research exists on the structure, lattice parameters, and density of high-pressure ice polymorphs, namely Ice VI and Ice VII, as these ices may make up a considerable part of the interior of large icy satellites and select extra solar planets; though most research thus far has been constrained to the pure H₂O system. Salty subsurface oceans are also believed to exist within some of these icy bodies which may have prolonged interaction with the Ice VII phase present, incorporating foreign ions or molecules into the lattice of high-pressure ices. Recent research concerning the effects that charged ions have on Ice VII has shown that the presence of these ions notably affects the structure, increasing the Ice VII molar density at any given pressure relative to pure Ice VII (Frank et al., 2006, PEPI, 155, 152-162). This study focused on the incorporation of CH₃OH into Ice VII to determine if the change in density was predominantly a result of charge-induced partial ordering of the hydrogen in Ice VII (as outlined in Frank et al., 2006) or if it was controlled solely by the addition of large foreign molecules into the lattice structure. Solutions of 1.60, 5.00 and 10.0 mol% CH₃OH in H₂O were loaded into a diamond anvil cell. The experiments were performed at GSECARS 13-BM-D at the Advanced Photon Source at Argonne National Laboratory. The unit cell parameters were measured using monochromatic X-ray radiation, 0.3344 Å, and a MAR 345 online imaging system. Powder diffraction patterns were collected in ~1 GPa increments up to ~31, ~48, and ~35 GPa, respectively. The volume-pressure relations (at 300 K) were used to determine an equation of state (EOS) for select compositions in the CH₃OH - H₂O system. Diffraction data indicate that the unit cell volume of Ice VII formed from a 1.60 mol% CH₃OH aqueous solution did not deviate significantly from that of Ice VII formed from pure H₂O. Conversely, the volumes of Ice VII formed from 5.00 and 10.0 mol% solutions had reduced unit cell volumes relative to pure Ice VII. Zero-pressure volumes and bulk moduli were calculated with a pressure derivative fixed (4.40): 1.6 mol% CH₃OH - H₂O had values of 40.4±0.2 ų and 24.4±0.7 GPa, respectively, whereas 5.0 mol% CH₃OH - H₂O had values of 39.2±0.2 ų and 26.2±0.5 GPa, respectively. We hypothesize that charged ions will have a greater influence at lower concentrations on the properties of Ice VII than neutral species due to electrostatic interactions within the unit cell and crystallographic constraints imposed by the body-centered cubic structure of Ice VII. In conclusion, these results suggest that ice-phases formed in a solute-rich environment (or by reaction with other phases within the interior of an icy body) will most likely have a greater molar density than ice formed from pure H₂O.
DE: 5422 Ices
DE: 5430 Interiors (8147)
DE: 5460 Physical properties of materials
DE: 6218 Jovian satellites
DE: 6223 Callisto
SC: Mineral and Rock Physics [MR]
MN: 2007 Fall Meeting