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Publication - Dr Terence McMaster

    In situ atomic force microscopy measurements of biotite basal plane reactivity in the presence of oxalic acid

    Citation

    Simon, H, Mark, S, Vala, R, Jonathan, L, Steven, B & McMaster, T, 2011, ‘In situ atomic force microscopy measurements of biotite basal plane reactivity in the presence of oxalic acid’. Geochimica et Cosmochimica Acta, vol 75., pp. 6870 - 6881

    Abstract

    We have used a direct imaging technique, in situ atomic force microscopy (AFM), to observe the dissolution of the basal biotite surface by oxalic acid over a range of temperatures close to ambient conditions, using a specially designed AFM liquid cell and non-invasive intermittent contact mode of operation. From the 3-dimensional nanometre-resolution data sets, we observe a process characterised by the slow formation of shallow etch pits in the (001) surface and fast growth of etch pits from the resulting steps, which represent proxies for the {h k 0} surface. Measurements of dissolution rates as a function of temperature allow a determination of an apparent activation energy (E(a, app)) for the process, via mass-loss calculations from image analysis. We obtain a value of E(a, app) = 49 +/- 2 kJ mol(-1), which is consistent with separate calculations based on planar area etch pit growth, and measurements of etch pit perimeters, indicating that this value of E(a, app) is representative of {h k 0} surface dissolution. The measurement of etch pit perimeters also enables an estimation of apparent activation energy as a function of step density indicating substantially higher apparent activation energy, up to E(a, app) = 140 kJ mol(-1), on extrapolation towards a pristine surface with no defects. We suggest that this higher value of E(a, app) represents the slow formation of etch pits into the (0 0 1) surface.

    Full details in the University publications repository