Tmh. Costa et al., INFRARED AND THERMOGRAVIMETRIC STUDY OF HIGH-PRESSURE CONSOLIDATION IN ALKOXIDE SILICA-GEL POWDERS, Journal of non-crystalline solids, 220(2-3), 1997, pp. 195-201
High density, transparent, crack-free and hard compacts of silica gel
were produced by compaction under nearly hydrostatic environment at 4.
5 GPa, at room temperature. The starting material was used three days
after synthesis by hydrolysis of alkoxides without additional treatmen
t. Fourier transform infrared spectroscopy (FTIR), using the KBr techn
ique and a high vacuum cell at temperatures up to 450 degrees C, and t
hermogravimetric analysis (TGA) up to 900 degrees C was conducted. A r
eduction up to 60% in the adsorbed water content of the compacted sili
ca gel was observed. Changes in the 3000 to 3800 cm(-1) region indicat
e that the surface silanol groups became bridged, which promotes conde
nsation reactions of dehydroxylation. Those results suggest that the m
echanism for consolidation under high-pressure, is 'cold sintering' pr
ocess, where silanol groups at the surface of the nanoparticles conden
se to form siloxane bonds between the particles and water, resulting i
n a stiff body with closed nanopores containing trapped water. (C) 199
7 Elsevier Science B.V.