27Al and 29Si NMR (Nuclear Magnetic Resonance) Study of Sol-Gel Derived Aluminosilicates and Sodium Aluminosilicates

摘要

The sol-gel process using metal alkoxides is being extensively explored as a method for the preparation of homogeneous multicomponent glasses In this context, such questions as homogeneity at the atomic level and structural differences between sol-gel and coventionally prepared materials are of great interest. Nuclear magnetic resonance (NMR) spectroscopy is a powerful technique for the study of multicomponent sol-gel systems. Solid state aluminum and silicon 29 NMR was used to examine the structures of aluminosilicates and sodium aluminosilicates prepared by the sol-gel method from metal alkoxides. In contrast to the borosilicate system, where B-O-Si bonds are not formed until heat treatment above 150 C, AL-O-Si formation appears complete upon gelation. Aluminium occupies tetrahedral (ALO4)(-) sites in the polymer network and octahedral (AL(H2O)6)(3+) (or similar) sites in the intersticies for charge balance. When sodium is added as a counter ion the octahedral aluminum is converted to tetrahedral aluminium in the oxide network. In gels of high aluminium content prepared from (Bu(s)O)2-AL-O-Si(OEt)3, some aluminum in five coordinate environments is also observed. All gels remain amorphous on heating to 800 C. Reprints.