『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 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 nm-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 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 substantially
higher activation energy, up to 80 kJ mol-1, when the
edge pits are in an incipient stage.』
Introduction
Methods
Atomic force microscopy
Data analysis
Results
Conclusions
Acknowledgements
References