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High-resolution imaging of biotite dissolution and measurement of activation energy

Published online by Cambridge University Press:  05 July 2018

T. J. McMaster ,
M. M. Smits ,
S. J. Haward ,
J. R. Leake ,
S. Banwart  and
K. V. Ragnarsdottir
T. J. McMaster*
Affiliation:
H.H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, UK
M. M. Smits
Affiliation:
Department of Animal and Plant Sciences, Alfred Denny Building, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
S. J. Haward
Affiliation:
H.H. Wills Physics Laboratory, University of Bristol, Bristol BS8 1TL, UK Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen’s Road, Bristol BS8 1RJ, UK
J. R. Leake
Affiliation:
Department of Animal and Plant Sciences, Alfred Denny Building, University of Sheffield, Western Bank, Sheffield S10 2TN, UK
S. Banwart
Affiliation:
Department of Civil and Structural Engineering, Kroto Research Institute, North Campus, University of Sheffield, Broad Lane, Sheffield S3 7HQ, UK
K. V. Ragnarsdottir
Affiliation:
Department of Earth Sciences, University of Bristol, Wills Memorial Building, Queen’s Road, Bristol BS8 1RJ, UK
*
*E-mail: [email protected]
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Abstract

We have used a direct imaging technique, in situ atomic force microscopy(AFM) to observe the earliest stages of the dissolution of a biotite surface byoxalic acid at temperatures close to ambient conditions, using a speciallydesigned AFM liquid cell and non-invasive intermittent contact mode of operation. From the nm-resolution data sets in x, yand z dimensions, we have measured dissolution rates and determined activation energies for the process as a function of temperature, via a mass-loss calculation. The value of Ea obtained, 49±2 kJ mol-1, appears to be too high to indicate a diffusion-controlled process and is more in line with expectations based on a process limited by the rate of ligand-induced metal cation detachment from the (001) surface. This is consistent with visual observations of the relative rates of etch-pit formation and growth, and accepted knowledge of the biotite crystal structure. Separate calculations based on planar area etch-pit growth, and measurements of etch-pit perimeters confirm this result, and also indicate substantiallyhigher activation energy, up to 80 kJ mol-1, when the edge pits are in an incipient stage.

Type
Research Article
Information
Mineralogical Magazine , Volume 72 , Issue 1 , February 2008 , pp. 115 - 120
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2008

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