Graded Porous Silicon Carbide for High Temperature Membrane Applications

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Graded Porous Silicon Carbide for High Temperature Membrane Applications Jyothi Suri and Leon L. Shaw Department of Chemical, Materials and Biomolecular Engineering, University of Connecticut, Storrs, Connecticut 06269, USA ABSTRACT Due to its excellent thermal shock resistance, mechanical and chemical stability at both room and elevated temperatures, silicon carbide (SiC) is an attractive material for environmental protection and energy production applications such as catalyst supports, molten metal filters and gas separation membranes. Precise pore size control and high porosity are the key deciding factors for such applications. In this study, we demonstrated the fabrication of bi-layered SiC membranes with a graded porosity, consisting of porous nano-SiC layer on the surface of a porous coarse-grained SiC support layer. Nano-SiC powders utilized for this study were synthesized using a novel process based on mechanical activation of silica fume and graphite mixtures, resulting in particle sizes as small as 30 nm. The effects of sintering temperature were investigated to control the pore size, particle size and overall density of the bi-layered membrane. INTRODUCTION Silicon carbide (SiC) is a promising candidate for a variety of inorganic membrane applications in energy production and environmental protection such as diesel particulate filters, hydrogen permselective membrane supports, due to its unique combination of properties such as high thermal conductivity [1], thermal shock resistance [2], biocompatibility [3], resistance to acid and basic environments [4], and chemical inertness. In addition to these properties, strength is an important factor for allowing high-pressure operations and the high mechanical strength of SiC ceramics [5] makes it potentially advantageous for membrane applications. Previous studies [6,7] have shown that it is possible to make SiC membranes with layer-wise decrease in pore sizes from several hundred nanometers in the macro-porous support to few nanometers on the top nano-porous SiC layer. In the present study, SiC membranes with a layered porosity structure were investigated. The membranes consisted of a macro-porous SiC support from commercially coarse-grained SiC powders and a porous nano-SiC layer on the surface of the macro-porous support. How the particle size and pore size changed with sintering temperature was studied in particular. The layered porous structure was achieved using conventional pellet pressing method and alumina as the sintering additive for both the commercial and nano-SiC powders. It was shown that the pore size and particle size of the membranes have increased with increase in the sintering temperature. This work lays a solid foundation for making tri-layered SiC membranes with a mesoporous SiC-N thin film on the top of the nanoporous-SiC layer in the near future. This study also paves the way for making large scale tubular tri-layered SiC porous supports using slip-casting technique in the future.

EXPERIMENTAL DETAILS The macroporous SiC support layer