Specialized Atomic Force Microscope Enables Studies of Mineral-Fluid Interfaces in Supercritical Carbon Dioxide


Among the options for reducing the emission of greenhouse gases such as carbon dioxide to the atmosphere is the injection of supercritical CO2 into the deep subsurface for long-term storage. However, some scientists wonder whether ongoing geochemical processes in the subsurface will ensure that the supercritical CO2 would remain sequestered. Efforts to study these processes require instrumentation that can handle samples at supercritical CO2 pressure and temperatures. In response to this need, a team of scientists from the Environmental Molecular Sciences Laboratory (EMSL), a DOE scientific user facility in Richland, WA, Wright State University, and Lawrence Berkeley National Laboratory has developed a high-pressure atomic force microscope (AFM) that enables the first-ever measurements of the atomic-scale topography of solid surfaces that are in contact with supercritical carbon dioxide (scCO2) fluids. Obtaining in situ, atomic-scale information about mineral-fluid interfaces at high pressure is particularly useful for understanding geochemical processes relevant to carbon sequestration. The ability to take in situ images as a function of time allows researchers to measure atomic-scale reaction rates by visualizing the dynamic processes that occur on the mineral surface and eliminates the need to alter experimental conditions between images. The new apparatus significantly extends the ability to make AFM measurements in environmental conditions not previously possible (in either commercial AFM instruments or in the few specially designed hydrothermal AFMs), and is designed to handle pressures up to 100 atmospheres at temperatures up to approximately 350 degrees Kelvin. The research team demonstrated the new microscope by imaging the disappearance of a hydrated calcium carbonate film on the calcite mineral surface in scCO2. The team met the technical challenge of maintaining precise control of pressure and temperature in the fluid cell, which is necessary to mitigate noise associated with density changes in a compressible fluid. The new apparatus can be used to study other gaseous or aqueous high-pressure solid-fluid chemical processes in addition to geochemical processes.

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Lea, A. S., S. R. Higgins, K. G. Knauss, and K. M. Rosso. 2011. “A High-Pressure Atomic Force Microscope for Imaging in Supercritical Carbon Dioxide,” Review of Scientific Instruments 82, 043709; DOI:10.1063/1.3580603.