Fabrication of silicon carbide sintered supports and silicon carbide membranes.

摘要

Efficient separation of hydrogen (H2) under high temperatures and pressures is important to the development of the clean-energy industry, and has been among the key drivers for research on inorganic membranes for the last two decades. Although substantial efforts have been devoted to date to the preparation of nanoporous membranes for H2 separation, the fabrication of high-temperature and steam-stable inorganic membranes with high hydrogen fluxes and large separation factors still remains a key challenge. Among all the potential candidates, silicon carbide (SiC) membranes show potential advantages for use in hydrogen separation processes under harsh and corrosive conditions such as, for example, the steam reforming and the water gas shift reactions commonly employed in H2 production; this is because SiC is a material that has high corrosion resistance, high thermal conductivity, high thermal shock resistance, and excellent chemical and mechanical stability, making it thus a promising material for application in industrial processes for clean energy production.;High-quality porous SiC supports are of great importance in the fabrication of hydrogen permselective SiC nanoporous membranes and their preparation has, thus, been a keen a key focus in this research. In this Thesis, we report on the preparation, via the pressureless sintering of beta-SiC powders, of SiC tubular supports that are both highly permeable and mechanically strong. Their transport characteristics were studied via inert-gas permeation tests, while their structure and surface morphology were characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM) analysis. In addition, the effect of varying the composition of starting powders, the sintering temperature, and the amount of sintering aids utilized on the transport characteristics and the surface roughness of such sintered SiC porous supports were also systematically investigated. These tubular SiC supports exhibit high fluxes (a He permeance as high as 5.8x10-5 mol·m-2·s -1·Pa-1) and are mechanically strong (compressive strength as high as 106 MPa) to potentially withstand the pressure drops required in their use as membrane supports.;Utilizing these high-quality SiC sintered supports, nanoporous SiC membranes were prepared by the pyrolysis of thin ally-hydridopolycarbosilane (AHPCS) films coated on such supports, using a combination of slip-casting and dip-coating techniques coupled with periodic coatings of polystyrene sacrificial interlayers. The membranes prepared using these SiC supports are very permselective (a He/Ar separation factor as high as 2000) and exhibit a He permeance as high as 2.4x10-7 mol·m-2·s -1·Pa-1.