Raman microscopy of dickite, kaolinite and their intercalates†

Abstract

Raman microscopy has been used to study kaolinites and dickites and their intercalates and to identify dickites in kaolins at low concentrations. During the intercalation, with potassium acetate, of a low defect structure kaolinite, several crystals provided significantly different Raman spectra. This led to the proposition that during the kaolinite intercalation process, some dickite crystals in the kaolinite were also intercalated. Raman bands at 3631 and 3640 cm–1 for the dickite were observed, corresponding well with standard dickite bands. The kaolinite intercalate showed upon intercalation, an additional Raman band at 3605 cm–1 with a consequential marked decrease in the Raman intensity of the bands at 3652, 3670, 3684, and 3693 cm–1 assigned to the vibrational modes of the inner surface hydroxyl groups. Additional Raman bands for the intercalated dickite were observed at 3609 and 3599 cm–1. These bands are attributed to the formation of a strongly hydrogen bonded complex between the inner surface hydroxyl groups of dickite and the carboxyl groups of the potassium acetate. The intensity of the 3685 cm–1 band was reduced to a minimum and the other three inner surface hydroxyls with Raman bands at 3652, 3670, and 3693 cm–1 were absent in the dickite spectra. Pronounced changes in the low frequency region for both intercalates were observed.