Silicon oxycarbide ceramics with reduced carbon by pyrolysis of polysiloxanes in water vapor

SiOC ceramics pyrolyzed from polysiloxanes are usually black because of the formation of excess carbon in the ceramic network. Here we show that the pyrolysis of polysiloxanes in water vapor significantly reduces carbon from SiOC and yields a white SiOC ceramic. Chemical analysis shows the amount of carbon in the white ceramic is only half of that in the black one pyrolyzed in argon. ²⁹Si nuclear magnetic resonance spectral (NMR) analysis indicates the reduction of the carbon-rich SiC₄] and SiC₂O₂] units with the enhanced formation of the oxygen-rich SiO₄] and SiCO₃] units by the water pyrolysis. Importantly, this water pyrolysis resultant carbon reduction is realized in a bulk polysiloxane, and the white SiOC ceramic is obtained in a bulk body with the retained shape of the precursor body. The water pyrolysis can be adopted as an effective mean to tailor the structure of PDCs via the simple introduction of water vapor in pyrolysis.