Thermal evolution of hybrid organic-inorganic gels derived from reaction of 1,4 butanediol with tetraethoxysilane

Transparent monolithic discs of organic-inorganic hybrid gels have been pre pared by hydrolysis-condensation reactions of tetraethyl orthosilicate with 1,4 butanediol. The gels and glasses have been characterized by infrared s pectroscopy and Si-29 MAS NMR. The characterization of the gels by infrared spectroscopy showed the incorporation of carbonaceous groups in the polyme ric structure and Si-C bonding in the glasses. Pyrolysis of the gels has be en studied using thermal analysis. It showed that the pyrolysis of the gels occurs in two temperature domains. The first is below 400 degrees C due to condensation reactions and second is in the temperature range 450-550 degr ees C due to decomposition of carbonaceous groups and crosslinking. Pyrolys is of the gels at 1000 degrees C resulted in X-ray amorphous, hard black gl asses similar to oxycarbide glasses obtained by pyrolysis of siloxanes. On further heat treatment to 1400-1600 degrees C, development of cristobalite structure and crystalline silicon carbide is observed in the otherwise amor phous black mass. The pyrolysed materials have been found to exhibit good r esistance towards oxidation at 1000 degrees C.