CHARACTERIZATION OF THE SIO2-GEL GLASS-FORMING PROCESS BY HIGH-RESOLUTION H-1-NMR IN SOLIDS

The gel-forming and gel to glass transition processes of the one-component gel-glass SiO//2 are studied by 270 MHz **1H NMR using the multiple-pulse cycle BR-24, after D. P. Burum and W. K. Rhim, in combination with magic angle spinning. The chemical shift for CH//3, CH//2, H//2O and OH groups allows the characterization of different steps of the hydrolysis and polycondenzation which depend on the ratio H//2O/tetraethylorthosilicate, from acid content, temperature and time. From the NMR data, in combination with DTA, TGA and porosity measurements of the gel glass obtained by heat treatment of the gels up to 1173 K, it is concluded that the chemical-shift values in the range 2-4 ppm (relative to TMS) and anisotropies DELTA sigma less than 5 ppm indicate non- or only slightly hydrogen-bonded SiOH groups.