Journal
MINERALOGICAL MAGAZINE
Volume 72, Issue 1, Pages 115-120Publisher
MINERALOGICAL SOC
DOI: 10.1180/minmag.2008.072.1.115
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Funding
- Natural Environment Research Council [NE/C521001/1, NE/C004566/1, NE/C521044/1] Funding Source: researchfish
- NERC [NE/C004566/1, NE/C521044/1, NE/C521001/1] Funding Source: UKRI
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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 by oxalic acid at temperatures close to ambient conditions, using a specially designed AFM liquid cell and non-invasive intermittent contact mode of operation. From the run-resolution data sets in x, y and 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 E-a 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 substantially higher activation energy, up to 80 kJ mol(-1), when the edge pits are in an incipient stage.
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