THE EFFECT OF MOLECULAR-OXYGEN ON THE SPIN-LATTICE RELAXATION OF SILICON IN CONDENSED SOL-GELS

The spin-lattice relaxation times of silicon nuclei within amorphous silica were found to be strongly dependent on the ambient atmosphere. Silica with various surface chemistries and surface areas were prepared by the sol-gel process. Relaxation times of silicon nuclei ranged from 9.0 to 730 s depending on whether the samples were exposed to oxygen or nitrogen atmospheres. Samples exposed to air exhibited intermediate relaxation times. Chemically distinct silicons displayed unique relaxation times when exposed to a nitrogen atmosphere while displaying common relaxation times when exposed to an air or oxygen atmosphere. Attempts to correlate relaxation times to surface areas were complicated by changes in the surface structure of the materials. Molecular oxygen should be eliminated from these high-surface-area materials whenever their inherent relaxation times are measured. © 1993 by Academic Press, Inc.