HR: 1340h
AN: V43B-1578    [Abstracts]
TI: Optical metrology of nano-scale mineral dissolutions using a phase-shift interference microscope
AU: * Satoh, H
EM: hsatoh@ganko.tohoku.ac.jp
AF: Tohoku University, Aoba-ku, Sendai, 980-8578 Japan
AU: Nishimura, Y
EM: nisimura@ganko.tohoku.ac.jp
AF: Tohoku University, Aoba-ku, Sendai, 980-8578 Japan
AU: Tsukamoto, K
EM: ktsuka@mail.tains.tohoku.ac.jp
AF: Tohoku University, Aoba-ku, Sendai, 980-8578 Japan
AU: Ueda, A
EM: a-ueda@mmc.co.jp
AF: Mitsubishi Materials Corporation, Omiya-ku, Saitama, 330-8508 Japan
AU: Ueta, S
EM: ueta@mmc.co.jp
AF: Mitsubishi Materials Corporation, Omiya-ku, Saitama, 330-8508 Japan
AU: Kato, K
EM: koikato@mmc.co.jp
AF: Mitsubishi Materials Corporation, Omiya-ku, Saitama, 330-8508 Japan
AB: Solid materials are greater or less soluble on the Earth's surface environment in nano-scale. Dissolution is critical issue for weathering and geo-environmental assessment. Recent advances in nanoscopy are derived from novel topographic method with scanning probe microscopes (AFM, STM, LCM). As another classical but precise method, interferometry is still useful optical tool and enables quick and easy survey of vertical surface topography by utilizing computer processing. We have newly designed a white-light phase-shift interference microscope (PSI-M) for detecting ultra-slow dissolution and precipitation to validate the endurance of artificial barrier system for radioactive waste repository (Ueda et al., 2005) and assess the geologic CO2 storage system. The measurement system is comprised of Maki-type (modified Michelson) phase-shift interferometer, white light source, computer camera, and Ti reaction cell with syringe pump. Minimum resolutions are calculated to be about 0.7 nm for surface-reflection mode and 6.6 nm for back-reflection mode. It takes only 2 s to obtain a phase-shift interferogram. After sequential image acquisitions, we can measure the rates of advance and retreat in real-time at the surface of the specimen in the view field by image-processing. As a benchmark test of surface reflection mode, we carried out a dissolution experiment on BK7 glass in pure H2O flowing at 105 um/s. Result showed 8.7E-5 nm/s of dissolution velocity, corresponding to a rate of ~3um/yr . Measurement at etch pits on calcite (10-14) in pure H2O showed an acceptable dissolution rate of 2.9E-10 mol/cm2/s (Ueda et al., 2005). Another measurement on anorthite (010) in 0.5M of NaCl-NaOH-HCl solutions at 105 um/s flow showed consistent rates of 2.4E-13 to 2.3E-11 mol/cm2/s at pH = 3-12.4 with the previous data (Blum and Stillings, 1995). These results sufficiently confirmed precision of the rate determination with PSI-M. We have further carried out the dissolution measurement on ~100x100x2 um3 smectite (Na-montmorillonite) in NaCl-NaOH solution (pH = 7-14) by back-reflection mode. The obtained rates at (001) were three-order faster (6.9E-10 to 3.6E-8 mol/m2/s) than the data previously reported (e.g., Cama et al., 2000; Yokoyama et al., 2005: ~1E-10 to 1E-12 mol/m2/s) and showed inhomogeneity. It has further been found that dissolution rate at etch-pit is three times accelerated than that at grain edge even at pH = 8. Flow-rate dependency on dissolution rates recognized in NaOH 1.0M solution but in the presence of Na2SiO3 (0.05 to 5.00 mM) suggests that the dissolution of smectite is strongly limited by Si release probably enhanced by flow. Thus, our established PSI-M system can be used to consider the mechanism concerning the dissolution and precipitation by controlling conditions of temperature, pressure, composition, and flow as present in natural system with 2D recognizing the dissolution step and pit.
DE: 1039 Alteration and weathering processes (3617)
SC: Volcanology, Geochemistry, Petrology [V]
MN: Fall Meeting 2005