Preparation, Characterization, and Modeling of Nanoporous Silicon Carbide Membranes

Silicon carbide (SiC) is a promising material for the preparation of high temperature membranes [1-5] due to its many unique properties such as high thermochemical stability, high thermal conductivity and resistance to abrasion. In our studies, SiC microporous membranes are fabricated using two different techniques. The first approach involves the pyrolysis of pre-ceramic polymeric films [3,4], which are coated on tubular SiC macroporous supports using a combination of slip-casting and dipcoating techniques. Combining slip-casting with dip-coating significantly improved the reproducibility in preparing high quality membranes. In addition, a novel method, based on the use of sacrificial interlayers, was also developed for the preparation of these SiC membranes, which involves periodic and alternate coatings of polystyrene sacrificial interlayers and SiC pre-ceramic polymeric layers on the top of slip-casted tubular SiC supports. Membranes prepared by this technique exhibit single gas ideal separation factors of He and hydrogen over Ar in the range of (176-420) and (100-200), respectively, with permeances that are typically two to three times higher than those of SiC membranes prepared previously by the more conventional techniques. The second approach in the preparation of microporous SiC membranes involves chemical-vapor infiltration/chemical-vapor deposition (CVI/CVD) techniques [2]. We have again used macroporous SiC tubes as supports, and a number of SiC CVD precursors. A key aspect of our studies, furthermore, involves the preparation of appropriate macroporous supports. We make use of novel binders which overcome the challenge of the nonhomogeneous distribution at the micro-scale one encounters with the current “state-ofthe-art” approaches. In our study, we investigate the effect on the final performance of the SiC supports of different parameters such as the starting SiC particle size distribution, the sintering aid content and sintering temperature. Optimized supports show two orders of magnitudes improvement in gas permeance compared to the SiC supports we prepared previously using the traditional approaches [1].