Sols were prepared in the system TMOS:H2O:SOLV:HC1 with molar
ratios of 1:4:3:0.0005 for SOLV = MeOH, EtOH and DMF. The gelation and aging
of these sols took place in cuvettes covered by parafilm. The gels were
removed from the cuvettes 14 days after gelation. Solvent exchange was
carried out in each of the three solvents for a period of 14 days. Starting
with fresh solvent, the exchange was repeated three times.
TGA and DTA curves were taken with pieces of the original gels and of gels
after the 2nd and 3rd solvent exchange. The TGA curves display a
considerable weight loss in the temperature range of solvent evaporation. A
small step is observed at higher temperatures if MeOH or EtOH represent the
exchange solvent. The DTA curves allow a distinction what mixtures of
solvents are present. The effectiveness of the solvent exchange can be
evaluated.