SI-29 MAS NMR INVESTIGATION OF THE NA2O-AL2O3-SIO2 GLASSES

Si-29 nuclear magnetic resonance (MAS NMR) on sodium aluminosilicate glasses with composition range of [Na]/[Al] greater-than-or-equal-to 1 were investigated. Line shapes and chemical shifts suggested that numbers of nonbridging oxygen atoms increase linearly with ([Na] - [Al])/[Si], in agreement with the classical structural model. An addition of alumina into sodium silicate glasses caused Si-29 chemical shift to lower field (less shielded) and increment of line width of Q(n) peaks with higher n value, where Q(n) represents the SiO4 tetrahedron with n bridging oxygen atoms connected to adjacent Si atom. It was suggested that aluminum atom tends to be coordinated with SiO4 tetrahedra of most polymerized states. The reaction between Q(n) structure units, 2Q(n) reversible Q(n-1) + Q(n+1), seemed to proceed to the left direction with increasing aluminum oxide contents as NaAlO2 into the sodium silicate glass.