29Si, 27Al, 1H and 23Na MAS NMR study of the bonding character in aluminosilicate inorganic polymers

Si-29, Al-27, H-1 and Na-23 solid-state magic-angle spinning (MAS) nuclear magnetic resonance (NMR) has been used to relate nominal composition, bonding character and compressive strength properties in aluminosilicate inorganic polymers (AIPs). The Si-29 chemical shift varies systematically with Si-to-Al ratio, indicating that the immediate structural environment of Si is altering with nominal composition. Fast H-1 MAS and Si-29 T (SiH)/T-1 rho relaxation measurements demonstrated that occluded pore H2O mobility within the disordered cavities is slow in comparison with H2O mobility characteristics observed within the ordered channel structures of zeolites. The Al-27 MAS NMR data show that the Al coordination remains predominantly 4-coordinate. In comparison with the Si-29 MAS data, the corresponding Al-27 MAS line shapes are relatively narrow, suggesting that the AlO4 tetrahedral geometry is largely unperturbed and the dominant source of structural disorder is propagated by large distributions of Si-O bond angles and bond lengths. Corresponding Na-23 MAS and multiple-quantum MAS NMR data indicate that Na speciation is dominated by distributions of hydration states; however, more highly resolved Na-23 resonances observed in some preparations supported the existence of short-range order. New structural elements are proposed to account for the existence of these Na resonances and an improved model for the structure of AIPs has also been proposed.