ChemInform Abstract: High-Resolution 27Al and 29Si MAS NMR Investigation of SiO2-Al2O3 Glasses

Abstract

{sup 27}Al and {sup 29}Si MAS NMR spectra have been obtained for SiO{sub 2}-Al{sub 2}O{sub 3} glasses quenched from the melt at two rates: 10{sup 5}-10{sup 6} {degree}C s{sup {minus}1} (SQ) and 10{sup 2}-10{sup 3} {degree}C s{sup {minus}1} (NQ). TEM experiments detected phase separation in the S{sub 76}A{sub 24}SQ and S{sub 52}A{sub 48} SQ samples but no phase separation for the S{sub 41}A{sub 59} SQ composition. The NQ glasses were phase separated and, in the diffraction TEM experiments, showed diffuse spots indicating microcrystallinity. {sup 27}Al spectra for the SQ glasses show three peaks due to aluminum in 4-, 5-, and 6-coordination, whereas NQ glasses show only peaks associated with aluminum in 4- and 6-coordination. Quantitative results for the {sup 27}Al spectra are discussed. The effect of spin speed on the {sup 27}Al MAS NMR spectra for SQ and NQ samples is demonstrated. Magnitudes of mean quadrupolar coupling constants and mean isotropic chemical shifts have been estimated. {sup 29}Si spectra of SQ glasses reveal a distribution of 4-coordinate Si sites, whereas NQ glasses show two inequivalent 4-coordinate sites.