NMR-STUDY OF KAOLINITE .1. SI-29, AL-27 AND H-1 SPECTRA

We have measured Si-29, Al-27, and H-1 NMR spectra of kaolinites with natural and synthetic origins, using high-resolution solid-state techniques such as the magic angle spinning and the multipulse sequences. The Si-29 spectra demonstrate clearly that two inequivalent Si sites are present, and the origin of the line width has been discussed quantitatively. The line shape of the Al-27 spectra is governed by the second-order quadrupole interaction and suggests the presence of two inequivalent Al sites with different quadrupole coupling constants and asymmetry factors. The H-1 static spectra are broadened by the dipole-dipole interactions between H-1 spins and between H-1 and Al-27 spins, indicating that the hydrogen atoms in the hydroxyl groups are in a rigid lattice state at room temperature. The technique of combined rotation and multiple-pulse spectroscopy has been successfully applied to kaolinites. The H-1 chemical shift of the hydroxyl groups is 2.8 ppm from tetramethylsilane.