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Structural heterogeneity of alkylammonium-exchanged, synthetic fluorotetrasilicic mica

Z. KAPYTA^1,*, A. GAWE¹, T. FUJITA² and N. IYI²

¹ Faculty of Geology, Geophysics and Environmental Protection, University of Mining and Metallurgy, al. Mickiewicza 30, 30-059 Krako 'w, Poland and ² National Institute for Materials Science, Namiki 1-1, Tsukuba, Ibaraki, 305-0044 Japan

^* E-mail: zklapyta{at}uci.agh.edu.pl

(Received 17 July 2001; revised 14 July 2002)

A series of organo-silicates was obtained from synthetic Na-fluorotetrasilicic mica (Na-TSM) by ion exchange with dodecyl-, tetradecyl-, hexadecyl- and octadecyltrimethylammonium (C12, C14, C16 and C18) bromides. When the concentration of the alkylammonium ions has varied from 0.43 to 3.4 mmol/g of the silicate, the maximum amount adsorbed on the mica was 0.92 mmol/g. As shown by ²³Na MAS NMR, ~0.30 mmol/g of Na⁺ ions were non-exchangeable, even if a large excess of the organic ions was used. The XRD patterns of all the samples obtained show that alkylammonium ions are distributed inhomogeneously within the mica interlayers. As a consequence, the organo-micas contain several phases consisting of randomly and regularly interstratified layers differing in terms of the amount of alkylammonium ions adsorbed. These different layers swell in ethylene glycol in the same manner and form new interlayers with identical spacings. The d₀₀₁ values of individual organo-TSMs after glycolation suggest that the alkylammonium ions are oriented perpendicular or almost perpendicular to the mica layers. The Na-TSM layers were not detected in organo-TSMs by XRD. The presence of organic and inorganic (Na) mixed-ion interlayers with spacings controlled by the arrangements of the organic ions is consistent with the results obtained. These data also suggest that the alkylammonium/Na⁺ ion ratios vary in alternate interlayers.

KEYWORDS: synthetic fluoromica, alkylammonium ions, ion exchange, interstratifications, structural heterogeneity