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New Views of High-pressure Meetings

Atomic force microscope enables in situ imaging of mineral-fluid interfaces in supercritical carbon dioxide

7 µm x 7 µm topographic images of the (1014) surface of calcite initially exposed to ambient air before imaging under scCO2 at 308.3 K and 82.0 atm. These images, taken 6 minutes apart, show the decomposition of a 1.2-nm film, presumably hydrated calcium carbonate, occurring on the calcite surface in anhydrous scCO2Enlarge Image

EMSL scientists, in collaboration with others, have  developed a high-pressure atomic force microscope (AFM) that enables the first-ever measurements—in-situ—of the topography of solid surfaces that are in contact with supercritical carbon dioxide (scCO2) fluids at atomic scale. Obtaining in situ information about mineral-fluid interfaces at high pressure is particularly useful for understanding geochemical processes—especially those relevant to carbon sequestration, a potential way to reduce greenhouse gas emissions. 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 atm at temperatures up to approximately 350 K. 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.  

Reference:  Lea AS, SR Higgins, KG Knauss, and KM Rosso.  2011.  “A High-Pressure Atomic Force Microscope for Imaging in Supercritical Carbon Dioxide.”  Rev. Sci. Instrum. 82, 043709; DOI:10.1063/1.3580603.

Acknowledgement:  The high-pressure AFM was developed as part of the In Situ Supercritical Suite funded by PNNL’s Carbon Sequestration Initiative. 

Learn more about EMSL's microscopy capability group.

Released: April 29, 2011