NMR-STUDY OF KAOLINITE .2. H-1, AL-27, AND SI-29 SPIN-LATTICE RELAXATIONS

Spin-lattice relaxation times of H-1, Al-27, and Si-29 spins in kaolinites with various origins have been measured at room temperature. Relaxation by paramagnetic impurities is dominant in those spins. Spin diffusion plays an important role in the H-1 and Al-27 relaxations, and their relaxations belong to the diffusion-limited case. Si-29 spins relax through the dipole-dipole interaction with electron spins directly, and the contribution of the spin diffusion is negligible. A part of the electron spins having an ESR signal at g = 4.1 play the role of relaxation centers. We have analyzed the relaxation times theoretically and have estimated the concentrations of paramagnetic impurities and the spin-lattice relaxation time of the electron spins.