REMEMBRANCES OF THINGS PAST - SILICON AND SODIUM LOCAL ENVIRONMENTS IN SOLS, GELS, GLASSES AND AQUEOUS-SOLUTIONS

The distribution of silica species has been determined by 29Si high resolution and magic angle spinning NMR in a sol, gel, glass, and solution made from a commercially available soluble sodium silicate solution. The present results indicate that silicon remembers its past: the species distribution of a solution, prepared by dissolution of the glass, is comparable to that of the starting solution. The species distribution of the gel made, from the soluble sodium silicate solution by drying & 80°C is identical to that of the starting solution. Heating this gel to temperatures {succeeds above single-line equals sign} 80°C causes polymerization of silica resulting in a distribution comparable to that of sodium silicate glass. 23Na nutation NMR shows the presence of primarily two different sodium environments: one with a small quadrupole interaction prevailing at room temperature, and another with a large quadrupole interaction occuring in gels dried at higher temperatures. The latter environment is the only one remaining in the glass made from the gel. © 1990.