HR: 0830h
AN: V51H-0368    [PDF]
TI: A New Optical Cell for Spectroscopic Studies of Geofluids at Pressures up to 100 MPa
AU: * Chou, I
EM: imchou@usgs.gov
AF: U.S. Geological Survey, 954 National Center, Reston, VA 20192 United States
AU: Burruss, R C
EM: burruss@usgs.gov
AF: U.S. Geological Survey, 956 National Center, Reston, VA 20192 United States
AB: Interpretation of Raman and fluorescence spectra of hydrocarbon fluid inclusions and spectroscopic observations of reactions in hydrocarbon-water systems require high quality reference spectra of individual gases, gas mixtures, and hydrocarbon-water systems. We constructed a new optical cell from a square flexible fused silica capillary tube (300 $\mu$m x 300 $\mu$m with 100 $\mu$m x 100 $\mu$m cavity) and a high-pressure valve that allows studies of fluids at room temperature and pressures up to 100 MPa. The cell has several advantages over existing ones, including the hydrothermal diamond-anvil cell, and they are: (1) ability to directly load sample fluids and monitor pressure during investigation; (2) no optical distortion; (3) small cell volume suitable for samples of limited supply (e.g., commercially available gas mixtures); (4) high pressures can be achieved; (5) a high-magnification, high-numerical-aperture objective lens (e.g., 100x) with a short working distance can be used due to the thin wall of the capillary tube, and (6) a heating-cooling stage can be added, allowing for investigations at temperatures other than room temperature, particularly suitable for studies of gas hydrates. Raman spectra have been collected from the cell for methane, ethane, propane, n-butane, and also for two gas mixtures containing up to 9 components as a function of pressure up to 41 MPa. The spectra document the shift in Raman bands with pressure as well as constrain the detection limits for various gas species in the mixtures. Preliminary experiments on the diffusion of methane in water were conducted by monitoring the concentration of dissolved methane in water, as a function of time and distance from the vapor-water boundary, immediately after the perturbation of an equilibrium state induced by a sudden change in methane pressure.
DE: 1045 Low-temperature geochemistry
DE: 1055 Organic geochemistry
DE: 1094 Instruments and techniques
DE: 1099 General or miscellaneous
SC: Volcanology, Geochemistry, Petrology [V]
MN: 2003 Fall Meeting