Analysis of the Degree of Crystallinity of Aluminosilicates of the Kaolinite Subgroup According to the IR Spectroscopy Data

The data of X-ray diffraction and IR spectroscopy of synthetic aluminosilicates of the kaolinite subgroup with different degrees of crystallinity are analyzed. The samples are obtained under hydrothermal conditions in alkaline and neutral media with different durations of synthesis. It is shown that as the synthesis time increases a gradual transition of the amorphous phase to the crystalline phase is observed, which is reflected in the IR spectra by the shift of the bands related to the oscillations of the groups in the octahedral and tetrahedral grids. The first band of stretching vibrations of hydroxyl groups at 3628 cm^–1 appears after three days of hydrothermal treatment in a neutral medium, and under alkaline conditions with the same duration of treatment, two more bands are observed at 3687 and 3668 cm^–1. The detected changes in the IR spectra correspond to the appearance of the characteristic X-ray reflections of halloysite according to the XRD data. Thus, IR spectroscopy can be considered as a method for a qualitative assessment of the degree of crystallinity.