| Popis: |
We have extended the range and complexity of glasses formed by the combination of metalalkoxides by synthesizing a clear, homogeneous gel of albite (NaAlSi 3 O 8 ) composition and heat-treating it to make a densified glass. Systematic changes in 29 Si, 27 Al, and 23 Na NMR spectra of gels with heat treatment are similar to differences in published spectra of hydrated albite glasses with varying water contents. The 29 Si spectra showed one peak; if Q 3 (OH) species are present in the samples, it is not obvious in the spectra. Analysis of the rate of spin transfer in CPMAS experiments suggests a Si-H distance ~ 15% shorter than that seen in Q 3 (OH) species in silica gel. Both the 27 Al and 23 Na peaks show an increase in quadrupolar broadening with heat treatment of the gel. Two peaks are present in the 23 Na spectra for gels heat-treated to 300 and 500°C, possibly due to sites with different sodium coordination. It is proposed that the differences in spectra can be explained by the differences in volatile content of the samples (including water as either H 2 O or OH − , and organic species such as ethanol). In the fresh gels with high contents of these polar species, the sodium is fully coordinated by polar molecules, with hydrogens bonding to the bridging oxygens. The volatiles are removed with heating, allowing the structure to relax to a point closer to that of an anhydrous albite glass made from a quenched melt. |
