A B S T R A C T: Changes in the molecular structure of a highly ordered kaolinite, intercalated with urea and potassium acetate, have been studied using Raman microscopy. A new Raman band, attributed to the inner surface hydroxyl groups strongly hydrogen bound to the acetate, is observed at 3605 cm -1 for the potassium acetate intercalate with the consequential loss of intensity in the bands at 3652, 3670, 3684 and 3693 cm -l. Remarkable changes in intensity of the Raman spectral bands of the low-frequency region of the kaolinite occurred upon intercalation. In particular, the 144 and 935 cm -1 bands increased by an order of magnitude and were found to be polarized. These spectroscopic changes provide evidence for the inner surface hydroxyl group-acetate bond being at an angle approaching 90 ~ to the 001 face. Decreases in intensity of the bands at 243, 271 and 336 cm -1 were observed. The urea intercalate shows additional Raman bands at 3387, 3408 and 3500 cm -~ which are attributed to N-H vibrations after formation of the urea-kaolinite complex. Changes in the spectra of the inserting molecules were also observed.Clay minerals can interact with both organic and inorganic chemicals through a number of mechanisms such as adsorption, intercalation and cation exchange. The basic principles of intercalation reactions have been elucidated for kaolinite by Lagaly (1984). The reactive guest molecules enter the interlayer spaces and expand the kaolinite layers, essentially making the kaolinite into a single layered mineral. Reactive molecules have been classified into groups according to the point of clay interaction. Group A consists of those compounds which can form strong hydrogen bonds to the silicate layers, e.g. hydrazine, urea, formamide and acetamide. Group B consists of molecules with strong dipole interactions which can interact with the silicate layers and includes molecules such as dimethyl sulphoxide. Group C consists of the alkali salts of short chain fatty acids, in particular acetic and propionic acids (Weiss et al., 1966). In this paper one example from group A and one example from C have been selected for an intercalation study with a very highly ordered kaolinite.

Upon the intercalation of kaolinite with DMSO, new Raman bands at 3660, 3536, and 3501 cm-1 are observed for the low-defect kaolinite and at 3664, 3543, and 3509 cm-1 for the high-defect kaolinite. An additional band at 3598 cm-1 was observed for the high-defect kaolinite. The band at 3660 cm-1 was assigned to the inner-surface hydroxyls hydrogen bonded to the SO group. The other three bands are attributed to the hydroxyl stretching frequencies of water in the intercalation complex. The hydroxyl deformation region is characterized by one intense band in both the FTIR and Raman spectra at 905 cm-1. Significant changes in the Raman spectra of the intercalating molecule are observed. Splitting of the C−H symmetric and antisymmetric stretching vibrations occurs. Two Raman bands at 2917 and 2935 cm-1 and four bands at 2999, 3015, 3021, and 3029 cm-1 are observed. The in-plane methyl bending region shows two Raman bands at 1411 and 1430 cm-1. The DRIFT spectra show complexity in these regions. The SO stretching region shows bands at 1066, 1023, and 1010 cm-1 upon intercalation with DMSO for the low-defect kaolinite and 1058, 1028, and 1004 cm-1 for the high-defect kaolinite. The 1058 cm-1 band is assigned to the free monomeric SO group and the 1023 and 1010 cm-1 bands to two different polymeric SO groups. Bands attributed to the C−S stretching vibrations, the in-plane and out-of-plane SO bending and the CSC symmetric bends all move to higher frequencies upon intercalation. It is proposed that intercalation with DMSO depends on the presence of water and that the additional bands at 3536 and 3501 cm-1 are due to the presence of water in the intercalate.

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Intercalation complexes of three different Hungarian kaolinites with hydrazine and potassium acetate were investigated by FT-IR (DRIFT) spectrometry, X-ray diffraction, and thermogravimetry combined with mass spectrometry. Differences were found in the thermal behaviour of the complexes as well as in the rehydration -reexpansion patterns of the heated intercalates. An XRD method is proposed for the distinction of kaolinite and 7.2 A halloysite present in the same mineral.

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