Calcium boroaluminosilicate xerogels and glasses with an E-glass composition were synthesized using metal alkoxides and metal salt as precursors. Structural evolution during the gel-to-glass transition was monitored by FTIR and NMR spectroscopies. Kramers-Kronig analysis was performed on the FTIR specular reflectance data to yield the ε2 and Im(-1/ε) spectra for the xerogels and the glass. A xerogel treated at 600°C exhibits distinct structural characteristics relative to the glass. A significantly higher concentration of BIV is present in the xerogel due to the large amount of surface boranol groups. Another unique feature of this xerogel is revealed by a red-shift in the high-frequency LO mode of the Si-O stretching vibration relative to the dense glass. This shift is attributed to a surface mode in the vibrational spectrum which is a consequence of the high surface area and the particulate structure of the xerogel. A xerogel treated at 710°C has FTIR and NMR spectra that are similar to the dense glass. Thus, the bulk network structure of the glass is present in the 710°C xerogel. A higher surface area (∼ 40 m2/g) and concentration of isolated surface Si-OH and B-OH groups distinguish it from the dense glass. An important conclusion of this study is that the only fundamental difference between the 710°C xerogel and the glass is the surface of the xerogel. In this sense, monolithic xerogels can provide convenient substrates for studying the surface chemistry of multicomponent glasses.
All Science Journal Classification (ASJC) codes
- Electronic, Optical and Magnetic Materials
- Ceramics and Composites
- Condensed Matter Physics
- Materials Chemistry