Tuning the microstructure of polycarbosilane-derived SiC(O) separation membranes via thermal-oxidative cross-linking.

Schematic illustration showing the evolution of network structure for the cured and uncured PCS. • The microstructure of SiC-based ceramic could be precisely tailored via thermal-oxidative curing. • Either excessive or insufficient cross-linking could cause the micropores to collapse. • PCS membranes had high thermal stability and oxidation resistance at 500 °C. • The optimized PCS membrane had excellent gas permeation properties and displayed high performances for H 2 /C 3 H 8 separations. In this study, the physicochemical properties and microstructural variations of polycarbosilane (PCS) were systematically investigated at curing temperatures of 150–350 °C and pyrolysis temperatures of 350–850 °C. Oxidative cross-linking remarkably enhanced the thermal stability of the PCS structure. Elemental composition and microstructure of the final ceramic material could be precisely tailored via the air curing process. Cross-linking by air curing that is either excessive or insufficient could cause the micropores of the resulting ceramic material to collapse or disappear. The most promising PCS-derived membranes, which were cured at 250 °C and then pyrolyzed at 750 °C, had high thermal stability and oxidation resistance at 500 °C in addition to excellent permeation properties: H 2 permeance of 1–2 × 10−6 mol/(m2 s Pa) at 500 °C with H 2 /N 2 selectivity of 31 and H 2 /C 3 H 8 selectivity of 1,740; and, CO 2 permeance of 1.8 × 10−6 mol/(m2 s Pa) at 27 °C with CO 2 /CH 4 selectivity of 40. Moreover, permeance and selectivity in an equimolar H 2 /C 3 H 8 mixture at 500 °C were approximately the same as those in single gases, suggesting the separation mechanism could be ascribed to molecular sieving. This is the first study to propose the concept of tailoring the microstructure of SiC-based membranes by controlling the curing process. [ABSTRACT FROM AUTHOR]