Studies on evolution of nano SiC ceramics from allylborosiloxane

Allylborosiloxane preceramic oligomers with ceramic residue in the range 75-84% (at 900 °C) were synthesized through the condensation of phenyl boronic acid (PBA) with allyltriethoxysilane (ALTEOS) in three different monomer feed ratios. The oligomers were characterized by GPC, IR, viscosity, TGA and TG-MS techniques. There is an increase in ceramic residue with increase in ALTEOS and maximum residue of 84% was obtained for the oligomer synthesized from PBA and ALTEOS in 1:2 ratio. The oligomers were pyrolysed at 900 °C followed by heat treatment at 1500 °C and 1650 °C in inert atmosphere and were characterized by spectroscopic techniques. Even though SiC formation is observed at 1500 °C, conversion of SiBOC/SiOC to SiC is not complete at 1500 °C and the presence of silica and carbon phases are found in the ceramics. Spectral studies reveals that β-SiC with trace amount of α-SiC is formed when oligomers are heated at 1650 °C in argon atmosphere.