A Fifth OH-Stretching Band in IR Spectra of Kaolinites.

Transmission infrared spectra of different kaolinites were studied by curve fitting. These spectra generally exhibit four hydroxyl stretching bands. In this article we show that a fifth OH band (already identified in Raman and photoacoustic IR spectra of kaolinites) is also observed in transmission IR spectra of hydrothermal and authigenic kaolinites, which have a high degree of crystallinity. This additional band is weak or undetectable for kaolinites with a low degree of crystallinity. Copyright 1999 Academic Press.

Infrared Study of the Intercalation of Kaolinite by Caesium Bromide and Caesium Iodide.

CsBr- and CsI-kaolinite intercalation complexes were synthesized by gradually heating caesium halide disks of the DMSO-kaolinite intermediate up to 330 degreesC. Infrared spectroscopy revealed two types of complexes with the caesium salts: almost nonhydrous, obtained during thermal treatment of the DMSO complex, and hydrated, produced by regrinding the disk in air. Comparison of band positions for CsBr-kaolinite and CsI-kaolinite with those for the CsCl complex (observed in a previous study) shows that the strength of the hydrogen bond between the intercalated halide and the inner surface hydroxyl decreases on the order CsCl > CsBr > CsI. The nonreactivity of CsI in mechanochemical intercalation may arise from weak interaction between I- and inner surface hydroxyl groups, resulting from the fact that caesium is a very soft acid and iodide is a very soft base. Consequently, the very strong interaction between the two ions in the crystal is not disrupted during mechanochemical treatment. Copyright 1998 Academic Press and Minister of Natural Resources, Canada.