Characterization of the Pyrolysis Process and Structure of Silicon Oxycarbide Based Materials from Organically Modified Silicate Gels

摘要

Organically modified silicates (Ormosils) appear as precursors to prepare silicon oxycarbide based materials. These Ormosils were prepared from tetraethoxysilane (TEOS), silanol terminated polydimethylsiloxane (PDMS) and fumed silica, in different ratios by using the sol-gel method, and then pyrolysed in nitrogen atmosphere up to 1500 ℃ in order to obtain silicon oxycarbide materials. It was found that Ormosils are thermally stable in these conditions up to approximately 400 ℃. The transition between the hybrid material and the inorganic material occurs between approximately 600 and 1000 ℃. At 1000 ℃, silicon oxycarbide network is formed by [C_2SiO_2], [CSiO_3] and [SiO_4] sites and a polyaromatic free carbon phase. As the pyrolysis temperature increases, the amorphous silicon oxycarbide network and free carbon phase undergo structural rearrangements. At temperatures of 1400 and 1500 ℃, the network of pyrolysed materials is formed mainly by [SiC_4] and [SiO_4] sites and a nanocrystalline graphite-like phase.