Infrared spectroscopy as the method for determining structural responses of natural clays to microwave exposure
Purpose. Universal applicability of naturally occurring materials such as clays attracts attention for scientific studies of their properties. In this paper microwave induced response of clay particles sourced in Orenburg region is studied. Infrared spectrometry method was used to control structural-morphological transformation induced by microwave field treatment in naturally occurring phyllosilicates. Properties of layered alumosilicates sourced from different deposits differ significantly from the standard samples. The goal of this paper is to study interatomic bounds evolution induced by microwave field treatment and to identify spectral modes in naturally occurring clays that contain montmorillonite and kaolinite with similar chemical composition, but different phase structures. Methods and methodology. Clays containing more than 50 % of montmorillonite and kaolinite were treated by 750 W microwave field for 10 minutes in two regimes. Chemical bound evolution was evaluated via infrared spectrometry of KBr samples pressed into pill form, measurements were performed with infrared Fourier spectrometer. Results and conclusions. Infrared spectra of montmorillonite containing clay samples indicate existence of microwave induced structure changes. The spectral peak related with valence symmetric vibrations vanishes. Deformation unbridged bound Al-O-H (line 912 cm<sup>-1</sup>) vanishes after microwave treatment in dry air environment and reappears in a humid environment as Si-O-Si bound (line 1009 cm<sup>-1</sup>). Intensity of absorption lines related to valence vibration of Si-O-Si bound in SiO<sub>4</sub> tetrahedron (797 сm<sup>-1</sup>) and deformation vibrations of Si-O bounds in SiO<sub>4</sub> tetrahedron (533, 467, 428) are reduced by factors 1.5 and 1.8 correspondingly after microwave treatment in air and humid environments. Infrared spectra of kaolinite clays contain absorption lines, cm<sup>-1</sup>: 3620. 3424, 1032, 1008, and 912. Microwave treatment destroy the most part of bounds: in air environment their content is reduced by factor 1.8-2; in a humid environment by factor 2.5. Mainly dominate bounds in SiO<sub>4</sub> tetrahedra and bounds S(Al-O-H) are destroyed. Kaolinite clay is more susceptible to microwave treatment.