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Identification of Fragile Microscopic Structures during Mineral Transformations in Wet Supercritical CO2

Published online by Cambridge University Press:  07 February 2013

Bruce W. Arey ,
Libor Kovarik ,
Odeta Qafoku ,
Zheming Wang ,
Nancy J. Hess  and
Andrew R. Felmy
Bruce W. Arey*
Affiliation:
Pacific Northwest National Laboratory, P.O. Box 999, K8-80, Richland, WA 99354, USA
Libor Kovarik
Affiliation:
Pacific Northwest National Laboratory, P.O. Box 999, K8-80, Richland, WA 99354, USA
Odeta Qafoku
Affiliation:
Pacific Northwest National Laboratory, P.O. Box 999, K8-80, Richland, WA 99354, USA
Zheming Wang
Affiliation:
Pacific Northwest National Laboratory, P.O. Box 999, K8-80, Richland, WA 99354, USA
Nancy J. Hess
Affiliation:
Pacific Northwest National Laboratory, P.O. Box 999, K8-80, Richland, WA 99354, USA
Andrew R. Felmy
Affiliation:
Pacific Northwest National Laboratory, P.O. Box 999, K8-80, Richland, WA 99354, USA
*
*Corresponding author. E-mail: bruce.arey@pnnl.gov
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Abstract

This study examines the nature of highly fragile reaction products that form in low water content supercritical carbon dioxide (scCO2) using a combination of focus ion beam/scanning electron microscopy, confocal Raman spectroscopy, helium ion microscopy (HeIM), and transmission electron microscopy (TEM). HeIM images show these precipitates are fragile rosettes. Using the TEM revealed details on the interfacial structure between the newly formed surface precipitates and the underlying initial solid phases. Detailed microscopy analysis revealed that growth of the precipitates either followed a tip growth mechanism, with precipitates forming directly on the forsterite surface if the initial solid was nonporous (natural forsterite) or growth from the surface of the precipitates, where fluid was conducted through the porous (nanoforsterite) agglomerates to the growth center. Identification of the mechanism of formation of hydrated/hydroxylated magnesium carbonate compound phases is a key factor in unraveling the impact of water recycling on mineral reactivity in low water content scCO2 solutions, which has received a great deal of attention as a result of the potential for CO2 to act as an atmospheric greenhouse gas. Techniques used here to examine these fragile structures are also used to examine a wide range of fragile material surfaces.

Keywords

SEMTEMhelium ion microscopecarbon sequestrationCO2forsterite
Type
Materials Applications
Information
Microscopy and Microanalysis , Volume 19 , Issue 2 , April 2013 , pp. 268 - 275
Copyright
Copyright © Microscopy Society of America 2013

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