Spectroscopic study of ceramic precursors obtained by hydrolytic condensation of ethoxycyclotetrasiloxane

Abstract: Hydrolytic polycondensation process, also called sol–gel process, leads to formation of xerogels from simple molecules e.g. most widely used tetraethoxysilane (TEOS). In the presented work 2,4,6,8-tetraethoxy-2,4,6,8-tetramethylcyclotetrasiloxane – D4(OEt)4 was applied as the molecular precursor. Polycondensation reactions were performed in the presence of Bu4NF or HCl/NH4OH as the catalysts. The obtained xerogels were studied by FT-IR, MAS-NMR and XRD methods. Depending on the condensation process conditions, structure of the resulting materials varied from octahedral cage unit (T8) through a ladder chain to random structure. Dried xerogels were heated at the temperature of 800 and 1000°C in argon or air atmosphere (pyrolysis or ceramization). In the atmosphere of argon SiC x O y glass materials were obtained, while in air silica glass was formed. Their properties depended on the pyrolysis conditions as well as on the xerogel structure. IR spectroscopy results allowed to conclude about the short range order in amorphous xerogel and glass materials. [Copyright &y& Elsevier]