Microstructure evolution and enhanced permeation of SiC membranes derived from allylhydridopolycarbosilane

The evolution of the physicochemical properties of allylhydridopolycarbosilane (AHPCS) was systematically investigated via DLS, TG, FTIR, XRD, and EDS. AHPCS-derived membranes were prepared by coating AHPCS sols onto porous substrates, which was then followed by pyrolysis at 300–800 °C. The pre-crosslinking by thermal curing significantly increased the colloidal sol size of AHPCS in toluene solutions, which effectively reduced penetration into substrates and enhanced the gas permeation. Furthermore, the pore structure of AHPCS-derived membranes could be precisely tailored by the pyrolysis temperatures, and the results indicated that the structure of membranes could be roughly classified into one of three types: a dense polymer structure, a loose transitional structure, and a denser ceramic structure (here, the term ‘dense/denser’ refers to the small/smaller pore structure, while the ‘loose’ refers to the large pore structure). AHPCS-derived membranes prepared at 300–800 °C under a N₂ flow displayed superior H₂ permeance of (0.2–5) × 10⁻⁶ mol/(m² s Pa) at 200 °C with good H₂/N₂ selectivity of 12–56. Ceramic SiC membranes prepared at 700 °C showed an attractive H₂ permeance of (2–4) × 10⁻⁶ mol (m² s Pa)⁻¹ at 200 °C with H₂/N₂ selectivity of 16–22, H₂/SF₆ selectivity higher than 10,000, and N₂/SF₆ selectivity higher than 800. Moreover, the structure of the ceramic SiC membranes was highly stable with good oxidation resistance at 500 °C under air. AHPCS membranes prepared at 300–800 °C had different pore structures that exhibited a high level of quality and a variety of permeation properties that could provide many options for membrane materials over a wide range of applications.