Porous and ultrahigh surface area SiOC ceramics based on perhydropolysilazane and polysiloxane

Abstract Micro-/meso-porous ceramics with ultrahigh surface areas are highly desired in high-temperature applications. In this work, formation of porous silicon oxycarbide (SiOC) is studied based on perhydropolysilazane (PHPS) and polysiloxane (PSO) precursors. The PHPS can be chemically anchored to the PSO by hydrosilylation reaction, due to the extensive Si–H bonds from the PHPS. The presence of water vapor during pyrolysis not only accelerates the hydrolysis of the PHPS additive, but also facilitates the Si–O–Si bond formation within the SiOC. The resulting SiOC material has the highest specific surface area (SSA) of ∼2000 m2/g with an average pore size of 1.72 nm. The effects of the PHPS additive on the phase evolution and the resulting porous SiOC after hydrogen fluoride (HF) etching are investigated. 3D view of pore distributions qualitatively illustrates the PHPS effect on the SiO2 nanocluster formation in the SiOC. The difference between the experimental and calculated SSAs is explained based on the etchability and wall thickness of the SiO2 domains.