Preparation And Characterization Of Ceramic Membranes

Asymmetrical ceramic membranes are consisting of several layers of one or more different ceramic materials. They generally have a macroporous support, one or two mesoporous intermediate layers and a microporous top layer. The particular structure can form a defect-free microporous top layer with separation function, while reducing the permeation resistance of the whole membrane, and preparing membranes with good mechanical strength and permeation flux, which has industrial practical value. In this paper, porous silicon carbide, mullite/SiC and aluminum oxide ceramic support were prepared, of which the sintering kinetics was discussed by Makipirtti-Meng method, as well as the phase, microstructure, mechanical properties and filtration properties. The preparation of intermediate and separation layers were discussed, as well as a simple method to prepare γ-Al2O3 ultrafiltration membrane.Porous SiC ceramics made by sintering process were investigated by stepwise isothermal dilatometry (SID) measurement associated with X-ray diffraction (XRD) phase identification, scanning electron microscope (SEM) observation and mechanical properties analysis. The paper analyzed the step isothermal shrinkage data by Makipirtti-Meng method and the shrinkage data were found to fit well with the rate equation proposed in this method. Kinetic parameters were evaluated and sintering was found to occur through two major mechanisms of which the activation energies were 55.4 and 325.4 kJ/mol respectively, which relate to generation and sinter of oxidation products. Mullite/SiC composite ceramics were prepared using in situ reaction. The results show that the presence of mullite significantly strengthens the performance of silicon carbide ceramics, and best preparation method is to add 10wt% of Al(OH)3 and sintered at 1350℃ for 4 hours.Porous aluminum oxide ceramic support were prepared by adding pore-forming agent, and a certain amount of Al(OH)3 were added to optimize the mechanical properties of the substrate. The results show that propriety dosage of Al(OH)3 is 5wt%, and the porosity and flexural strength are increased with the increase of sintering temperature. Also, intermediate and separation layer were prepared using dip coating method, of which the mechanical properties, microstructure, permeate flux and pore size distribution were discussed, and found that the optimum sintering process for the intermediate layer is sintered at 1400℃ for 2 hours, and for the separation layer is sintered at 1200℃ for 2 hours.To solve the problem that complex hydrolysis and peptization reaction are necessary to produce boehmite colloidal system by traditional sol-gel method, a simple method was used in this paper by controlling the ratio of water-soluble polymer and aluminum nitrate, as well as the sintering process to prepare γ-Al2O3 ultrafiltration membrane. The results show that the ultrafiltration membrane sintered at 700℃ is preferably continuous and smooth with low porosity and its thickness is about 150nm. While the one sintered at 750℃ has higher porosity and gas flux of which the thickness is about 50nm, causing low strength and imperfect film.