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On the kinetics of ion exchange in phlogopite – an in situ AFM study

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Abstract:

The kinetics of cation exchange in phlogopite have been studied in situ by hydrothermal atomic force microscopy (HAFM). The exchange of interlayer K by octylammonium ions caused an increase in the interlayer distance and the formation of reaction fronts which can be locally resolved by AFM. The observed reaction fronts revealed substantial variations in their propagation rates – even within single interlayers. This observed variability in interlayer reactivity could mainly be attributed to chemical and structural inhomogeneities of the samples. A quantitative evaluation of the front propagation at representative sites yielded a diffusion coefficient of the K+ exchange by octylammonium of 1.2 ± 0.6 × 10– 11 cm2/s assuming negligible transport normal to the layers. The reverse reaction, i.e. the exchange of organic ions by K+, resulted in a retreat of the reaction fronts and a general restoration of the original morphological state. However, indications of structural alterations and areas with trapped octylammonium ions were found.

Keywords: ALKYLAMMONIUM; ATOMIC FORCE MICROSCOPY; CATION EXCHANGE; CLAYS; DIFFUSION; MICA; ORGANIC IONS; PHYLLOSILICATES; SURFACE ALTERATION; SWELLING

Document Type: Research Article

DOI: http://dx.doi.org/10.1346/CCMN.2007.0550401

Publication date: August 1, 2007

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  • The JOURNAL publishes articles of interest to the international community of clay scientists, including but not limited to areas in mineralogy, crystallography, geology, geochemistry, sedimentology, soil science, agronomy, physical chemistry, colloid chemistry, ceramics, petroleum engineering, foundry engineering, and soil mechanics. Clays and Clay Minerals exists to disseminate to its worldwide readership the most recent developments in all of these aspects of clay materials. Manuscripts are welcome from all countries.

    Clays and Clay Minerals is the official publication of The Clay Minerals Society.

    The Editor-in-Chief is Professor Joseph W. Stucki jstucki@illinois.edu

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