Hierarchically ordered micro/meso/macroporous polymer-derived ceramic monoliths fabricated by freeze-casting

A hierarchically-ordered macro/meso/microporous SiOC monolith was obtained via freeze-casting using commercial polysiloxane as a raw material and silica sol as a binder and template source. The pre-ceramic polymer polysiloxane was pyrolyzed at 600 °C to produce a hydrophilic surface; higher temperatures would fully decompose the organic groups. When silica sol and polysiloxane precursor were combined in freeze-casting method, after pyrolysis a polymer-derived SiOC ceramic monolith with a lamellar pore morphology and a hierarchically-ordered pore structure was obtained. Decomposition of the polysiloxane precursors results in the development of micropores, and particle packing is believed to be responsible for the mesopore formation. Macro/mesoporous hierarchically-ordered ceramics with a specific surface area of 74 m2/g are preserved at pyrolysis temperatures as high as 1000 °C. The influence of H44-derived filler amount (10 wt–40 wt%), freezing temperature (−20 °C, −80 °C, −150 °C), and pyrolysis temperature (600 °C, 700 °C, 1000 °C) on open porosity, pore size distribution, and surface characteristics were investigated.