Abstract:
This work deals with experimental and theoretical investigation of the spectral properties of smectite, and its mixture with alabaster (building gypsum) at low moistures. The position and intensity of infrared spectrum bands at wave numbers in the range of 800–1250 cm$^{-1}$ coming from Si–O vibrations are investigated. In order to interpret the experimental spectra obtained by frustrated total internal reflection method, theoretical models based on DFT with XLYP-correlation potential are used, with cluster approximation for the smectite surface. This allowed determining optimal positions of the atoms of CaSO$_4$ and H$_2$O molecules near the basal surface. Positions and intensities of components of the IR spectra of clusters are calculated. The profile of water valence bands was calculated as superposition of Gaussian curves with the widths estimated from the experiment. Theoretical studies explained the observed transformations of spectral bands (variation of positions and intensities) resulting from the modification of the surface properties of smectite particles, and from changes in samples moisture. The agreement achieved in the positions and profiles of experimental and theoretical spectral bands justifies the adequacy of the theoretical description of modification of smectite properties, and the effect of hydration.
Keywords:infrared spectrum, DFT method, basal surface modification, cluster method, electron and spatial structure.
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