| Silicon carbide (SiC) is a material with very attractive properties. Its excellent mechanical strength, high chemical stability and thermal conductivity, strength and abrasion resistance at high temperatures, low thermal expansion, biocompatibility, and resistance to acidic and alkali environments, have made SiC a great candidate for use as material for the preparation of high-temperature membranes.;The focus of the present Thesis is to prepare SiC microporous membranes by a chemical-vapor deposition technique (CVD), using tri-isopropylsilane as the precursor and Ar or He as inert carrier gas. In the experiments we prepared membranes with a He permeance ~10-7 mol/m2 .s.Pa and a He/Ar ideal separation factor ~10.0. We envision the SiC membranes that we prepare to be eventually utilized in reactive separation applications with the water-gas shift and methane steam reforming reactions, where the membrane must function in the presence of high-temperature steam.;A pore network model was also developed in order to describe the preparation of microporous SiC membranes by the CVD technique. The membrane's pore space was represented by a three-dimensional network of interconnected pores, in which the effective size of the pores was distributed according to a pore size distribution. The chemical reaction, the various transport processes, and the evolution of the pore sizes due to the deposition of SiC on the pores' internal surface during the CVD process were included in the model. The Maxwell-Stefan equations were used for describing the pore level transport processes, which include the Knudsen and hindered diffusion, as well as viscous flow. The effect of pore blockage was also taken into account. The simulator monitors the PSD as the membrane's structure evolves. Also computed was the carrier gas' permeance during the CVD process. Good agreement was found between the simulation results and our single-gas experimental permeation data. The results also indicate the fundamental significance of the pore blockage (i.e., the percolation effect) to the evolution of the membrane's structure.;We also used the CVD technique to prepare SiC nanotubes and to characterize their properties using the BET, XRD, and TEM techniques. The SiC nanotubes have a number of potential uses as components of mixed-matrix membranes and catalyst supports, as well as for electronic and sensor applications. In the preparation of the SiC nanotubes we utilized as substrates, Anopore(TM) inorganic membranes (Anodisc(TM)), which are composed of a high purity alumina matrix prepared by the electrochemical anodization of aluminum. |
