Pressure Induced Disorder in Kaolinite

Abstract

Changes caused by pressures between 0 and 20 K bar on two samples of kaolinite have been studied. Increased pressure causes the samples to lose crystallinity, shown by a decrease in the Hinckley, Lietard and reference intensity ratio indices, as well as by the crystallite size measured from the 001 reflection. Results from DTA and solid state NMR show slight or no differences between the compressed and natural samples. Nonetheless, thermogravimetry reveals that the pressure treatment lowers the temperature at which dehydroxylation begins, but, unlike the grinding process, pressure does not alter the OH content of the samples. As a result of the increase in pressure, the IR spectra of the samples show a gradual increase in the intensity of the band at 1104 cm -1 with respect to 1112 cm -1. An increase in intensity can also be observed in the band at 936 cm ~ with respect to the band at 912 cm -1. Examination by electron microscopy reveals the existence of a large number of defects such as fractures, bends and deformations of the sheets, etc.; these are responsible for the decrease in crystallinity.