Preparation of Porous Mullite Fibers for Support of Environmental Catalyst

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Porous materials made of glass fibers and ceramic fibers have high porosity and good permeability for fluid, and were applicable as filters and porous ceramics with high thermal stability and chemical durability. The functions are further expected to improve by increasing specific surface area of the fibers. Therefore, porous mullite fibers were prepared by crystallization and selective leaching of glass fibers because mullite has good thermal stability, oxidation resistance and high chemical durability. First, three kinds of etchent solutions, i.e.NaOH,HF-H_2SO_4 and HF-NH_4F were used in the selective leaching treatment and examined their selectivity by changing the concentration, temperature, solid/solution ratio and soaking time. As the results, HF-NH_4F solution was decided to be the best etchent solution among them. The porous properties of mullite fibers were examined by changing the crystallizing temperatures from 1100 to 1300ﾟC.Corresponded to these crystallizing temperatures, the surface areas obtained ranged from 12 to 32 m^2/g and the pore sizes ranged from 5 to 36 nm. In this way, porous properties of mullite fibers were found to be tunable by controlling the crystallizing temperature and soaking time. Since the pores prepared in the mullite fibers maintained up to firing temperature 1200ﾟC,the thermal stability of the porous mullite fibers thus obtained was very high level compared with those of the other porous materials.