KAOLINITE HYDROXYLS - A RAMAN MICROSCOPY STUDY

Raman microscopy of the kaolinite polymorphs was used to study single crystals and bundles of aligned crystals of kaolinite. The spectra of the hydroxyl stretching region were both sample and orientation depend ent. Kaolinites can be classified into two groups according to the rat io of the intensities of the 3685 and 3695 cm(-1) bands. No relationsh ip was found between the d-spacing and the crystal domain size measure ment from the 001 reflection and the Raman spectral intensities indica ting the Raman spectra are independent of d-spacing and crystallinity. However, a relationship of the crystallinity in the a-b direction and intensities of the 3685 and 3695 cm(-1) bands indicate that the relat ive position of one layer to the other determines the position of the inner surface hydroxyl groups and the hydrogen bonding with the oxygen of the opposite layer. A new hypothesis based on symmetric and non-sy mmetric hydrogen bonding of the inner surface hydroxyl groups is propo sed to explain the two inner surface hydroxyl bands centred at 3685 an d 3695 cm(-1). The bands at 3670 and 3650 cm(-1) are described in term s of the out-of-phase vibrations of the in-phase vibrations at 3695 an d 3685 cm(-1).