Mechanism of Gas Separation through Amorphous Silicon Oxycarbide Membranes

Polymer‐derived amorphous silicon oxycarbide (SiOC) ceramics are designed for hydrogen separation at high temperatures. To form amorphous SiOC top‐coating with the thickness of about 300 nm, tubular porous γ‐Al₂O₃/α‐Al₂O₃ substrates with gradient porosity are threefold coated by vinyl‐functionalized polysiloxane and pyrolyzed at 700 °C under argon. N₂‐physisorption measurement confirms formation of microporous material with a specific surface area of about 400 m² g_–1. Single gas permeance characterization of the SiOC membrane at 300 °C reveals H₂/CO₂ and H₂/SF₆ ideal permselectivities of about 10 and 320, respectively. The experimental gas permeance data are modeled using solid‐state diffusion (for He and H₂) and gas translational diffusion (for CO₂ and SF₆) mechanisms.