|AVS 57th International Symposium & Exhibition|
|In Situ Microscopy and Spectroscopy Topical Conference||Wednesday Sessions|
|Session:||In Situ Microscopy/Spectroscopy – In Situ Nanoscale Processes|
|Presenter:||S. Lea, Pacific Northwest National Laboratory|
|Authors:||S. Lea, Pacific Northwest National Laboratory
S.R. Higgins, Wright State University
K.G. Knauss, Lawrence Berkeley National Laboratory
K.M. Rosso, Pacific Northwest National Laboratory
|Correspondent:||Click to Email|
Capture and storage of carbon dioxide in deep geologic formations represents one promising scenario for minimizing the impacts of greenhouse gases on global warming. At issue is the ability to demonstrate that CO2 will remain stored in the geological formation over the long-term and so knowledge of mineral-fluid transformation rates is critical for this determination. The majority of previous research on mineral-fluid interactions has focused primarily on the reactivity of minerals in aqueous solutions containing CO2. However, caprock integrity would be dictated primarily by mineral interaction with supercritical CO2 (scCO2) as the buoyant phase slowly displaces or dessicates residual aqueous solution at these surfaces. Many of the mechanisms of mineral interfacial reactions with hydrated or water-saturated CO2 are unknown and there are unique challenges to obtain kinetic and thermodynamic data for mineral transformation reactions in these fluids.
A high-pressure atomic force microscope (AFM) is currently under development that will enable in-situ site-specific measurements of metal carbonate nucleation and growth rates on mineral surfaces in contact with scCO2 fluids. This apparatus is based on the hydrothermal AFM that was developed by Higgins et al.1, but includes some enhancements and is designed to handle pressures up to 1500 psi. The noise in our optically-based cantilever deflection detection scheme is subject to perturbations in the density (and therefore index of refraction) of the compressible supercritical fluid. Consequently, variations in temperature and pressure within the fluid cell can have a significant impact in our ability to discern atomic steps on mineral surfaces. We demonstrate with our test fluid cell that the equivalent rms noise in the deflection signal is similar to (and in some cases less than) the equivalent noise for an AFM in its ‘standard configuration’ under controlled pressures of ~80 bar and temperatures of 60-80 °C and therefore in-situ atomic scale imaging of mineral surfaces in scCO2 should be possible. This talk will also focus on recent progress in the development of this instrumentation, which will enable a unique platform for elucidating the role of water in mineral transformations, providing a means for determining effective kinetic constants.
1. Higgins, S. R.; Eggleston, C. M.; Knauss, K. G.; Boro, C. O., A hydrothermal atomic force microscope for imaging in aqueous solution up to 150°C. Review of Scientific Instruments 1998, 69 (8), 2994-2998.