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HIGH-RESOLUTION AL-27 AND SI-29 MAS NMR INVESTIGATION OF SIO2-AL2O3 GLASSES

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Abstract

Al-27 and Si-29 MAS NMR spectra have been obtained for SiO2-Al2O3 glasses quenched from the melt at two rates: 10(5)-10(6)-degrees-C s-1 (SQ) and 10(2)-10(3)-degrees-C s-1 (NQ). TEM experiments detected phase separation in the S76A24 SQ and S52A48 SQ samples but no phase separation for the S41A59 SQ composition. The NQ glasses were phase separated and, in the diffraction TEM experiments, showed diffuse spots indicating microcrystallinity. Al-27 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 Al-27 spectra are discussed. The effect of spin speed on the Al-27 MAS NMR spectra for SQ and NQ samples is demonstrated. Magnitudes of mean quadrupolar coupling constants and mean isotropic chemical shifts have been estimated. Si-29 spectra of SQ glasses reveal a distribution of 4-coordinate Si sites, whereas NQ glasses show two inequivalent 4-coordinate sites

Topics: QD
Publisher: AMER CHEMICAL SOC
OAI identifier: oai:wrap.warwick.ac.uk:22679
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