Solid‐state NMR Evidence of 4‐, 5, and 6‐Fold Aluminum Sites in Roller‐Quenched SiO ₂ ‐A1 ₂ O ₃ Glasses

Abstract

The structures of roller‐quenched SiO 2 ‐Al 2 O 3 glasses containing 10 to 50 wt% Al 2 O 3 were investigated by TEM and high‐resolution 27 Al and 29 Si magic angle sample spinning nuclear magnetic resonance (MASS‐NMR) spectroscopy. The chemical shifts observed in the NMR spectra of these phase‐separated (on the TEM scale) glasses provide evidence, for the existence of all three (4‐, 5‐, and 6‐jold) Al‐coordination units in these glasses and for the presence of A1 in both the Si‐rich and Si‐poor phases.