A pyrolysis heating rate based pressureless method for preparing dense and crack-free polymer-derived silicon oxycarbide bulk ceramics

Silicon oxycarbide (SiOC) ceramics are increasingly considered as an emerging class of materials that have the potential for thermal insulation application because of their high thermal resistance and low thermal conductivity. However, cracks and microchannels are likely to form during the preparation of SiOC ceramics, exerting negative impacts on their mechanical and thermal performances. In this study, a pyrolysis heating rate based pressureless method was proposed to prepare dense and crack-free polymer-derived SiOC bulk ceramics. Then effects of pyrolysis heating rate on phase compositions of the prepared SiOC ceramics were investigated. Characterization results showed that the bulk density increased with the decrease in pyrolysis heating rate, and dense and crack-free SiOC ceramics were successfully prepared as the rate decreased to 0.5 degrees C/min. Besides, phase compositions were independent of the pyrolysis heating rate. Moreover, thermal behavior investigation revealed excellent thermal performance of prepared dense and crack-free SiOC ceramics to 1600 degrees C. Though the geometry of the bulk ceramics was limited by the mold in this work, the proposed method is transferable to other polymer-derived ceramics (PDCs) systems to fabricate practical temperature-resistant structures with complex shapes.