| Porous ceramic is a kind of ceramic material with lots of pores. Compared with glass fiber and reticular metal materials, it has steady performance, good corrosion resistance, high selective permeability and long service life. It has a promising application in the future.In this paper, SiO2 based composite porous ceramic is prepared by compound processes of Sol-gel method and dipping method with polymer foams. TEOS, aluminium powder and boric acid are adopted to be main raw materials. Preparing process of A1OOH sol, SiO2 sol and compound sol are studied in this paper. Dipping volume in polymer foam is increased by multi-dipping method. Excess sol in polymer foam is removed by extruding and centrifugal method during dipping, and compound sol dipped to polymer foam is dried by microwave. Applying the cross experiment method, the influence of the concentration of A1OOH sol, boric acid and volume of sol dipping in the polymer foam on the porosity, mechanical property and structure of sintering bodies have been investigated. The variation of properties versus sintering temperature has also been taken into consideration. Further, honeycomb formed polymer foam is used to investigate the possibility of preparing porous walled honeycomb ceramic. The physico-chemistry transformation, phase distribution and microstructure of as-prepared porous ceramic foam are systematically characterized via TG-DTA, XRD, SEM and optical microscope. On the other hand, porosity, mechanical property, distribution of pore size and grain size are also developed respectively via Archimedes principle, lever principle ,BET and quantitative analysis method.It is indicated that the compound technology of sel-gel and organic foam dipping can prepare reticular SiO2 based porous ceramic, which have macroscopic pores of certain distribution and microscopic pores distributed evenly, The pore wall are formed by stacking of the thousands of tiny grains. Extra sol is removed by extruding and centrifugal method, which can raise uniformity of sol in polymer foam, and avoid efficiently the problem of cross-crack on the sintering bodies. Microwave is helpful to improve drying speed, which is useful to prepare even density and regular samples.In sintering bodies, cristobalite is the major phase. The addition of Al2O3 and B2O3 has a good influence on the formation of mullite, lowering of sintering temperature and enhancement of samples' strength. The addition of B2O3 has a bigger affection on property of sintering bodies than Al2O3. With increasing B2O3 content, more glass phase are appeared, which change dramatically the structure of the porosity and strength of the ceramic body. The same trend has been observed as respect to the variation of porosity and strength with increasing Al2O3 content, but the variation is more smoothly. Soaking volume of polymer foam also affect performance and pore size distribution of the sintering bodies directly. More sol is dipped, porosity and pore size become smaller, and strength increased. The elevation of sintering temperature is generally good for full oxidation of specimen. The porosity of the ceramic body vary with the temperature from 1150 C to 1280 C and have a peak value, while its strength increases steadily. |
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