Pyrolytic transformation of liquid precursors to shaped bulk ceramics

The pyrolysis behavior of polysiloxane liquids in transformation to shaped ceramic bodies has been studied through liquid casting, crosslinking, and pyrolysis. The control of crosslinking temperatures with a second heating allows the self-demolding of crosslinked polysiloxanes from casting molds to form shaped polysiloxane bodies with good bonding quality. Pyrolysis of the polysiloxane bodies at various temperatures yields dense shaped SiOC materials changing in appearances from colorless transparent to dark brown to dark, corresponding to different degrees of pyrolysis. This indicates the homogeneous transformation of the polysiloxane network during organic-to-inorganic transformation. The bulk pyrolysis characteristics including bonding quality, microstructures, densities and shrinkage are studied in association with the effect of pyrolysis temperatures and precursor chemistries. The structural evolution of the polymeric network is analyzed by 29Si NMR, 13C NMR and FTIR spectroscopy. Through controlling the crosslinking and optimizing precursors, we have achieved net-shaped bulk SiOC material with a relatively large dimension.