²⁹Si MAS NMR investigation of the Na₂O-Al₂O₃-SiO₂ glasses

²⁹Si nuclear magnetic resonance (MAS NMR) on sodium aluminosilicate glasses with composition range of [Na]/[Al] ≥ 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 ²⁹Si 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 ⇌ 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.