Aldushin, Kirill; Jordan, Guntram; Aldushina, Elena; Schmahl, Wolfgang W.
On the kinetics of ion exchange in phlogopite - An in situ afm study.
In: Clays and Clay Minerals, Vol. 55, No. 4: pp. 339-347
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The kinetics of cation exchange in phlogopite have been studied in situby hydrothermal atomic force microscopy (HAFM). The exchange ofinterlayer K by octylammonium ions caused an increase in the interlayerdistance and the formation of reaction fronts which can be locallyresolved by AFM. The observed reaction fronts revealed Substantialvariations in their propagation rates - even within single interlayers.This observed variability in interlayer reactivity could mainly beattributed to chemical and structural inhomogeneities of the samples. Aquantitative evaluation of the front propagation at representative sitesyielded a diffusion coefficient of the K+ exchange by octylammonium of1.2 +/- 0.6 x 10(-11) cm(2)/s A assuming negligible transport normal tothe layers. The reverse reaction, i.e. the exchange of organic ions byK+, resulted in a retreat of the reaction fronts and a generalrestoration of the original morphological state. However, indications ofstructural alterations and areas with trapped oetylammonium ions werefound.