A study of the structural and spectral characteristics of free and bound water in kaolinite

Abstract

The dependence of the Si–O stretching vibration line intensity in the IR spectrum of kaolinite on the humidity of this mineral has been experimentally investigated. The experimental data were interpreted on the basis of density functional theory (DFT) calculations with allowance for the real crystallographic features of the kaolinite sample, determined by structural analysis. Some specific features of the intensity behavior in the plastic state are revealed, which can be used to develop techniques for determining its limits. The differences in the O–H bond lengths and H–O–H angles for the H₂O molecules adsorbed by basal surfaces and located in the porous space of the mineral are determined. Based on the DFT data, it was found that bond lengths and bond angles for a water molecule adsorbed on the siloxane surface are systematically smaller than for a water molecule adsorbed on the hydroxyl surface.