Fabrication and properties of ultra highly porous cordierite with oriented micrometer-sized cylindrical pores by gelation and freezing method

Abstract

Cordierite with ultra high porosity and oriented micrometer-sized cylindrical pores was prepared using a novel gelation-freezing method. Gelatin (used as the gelation agent), water (for formation of pores), and cordierite powder were mixed and cooled at 7°C. The obtained gel was frozen at -20 or -50°C, was dried using a freeze drier under vacuum, and then degreased at 600°C and sintered at 1200-1400°C for 2 h. The porosity was determined to be 93-79%, and was dependent on the powder content in the gel and the sintering temperature. SEM observations of the sintered body showed the microstructure of orderly uni-directionally oriented micrometer-sized cylindrical cells. The cell size was 25-235 μm, and these values were confirmed by the freezing temperature. The numbers of cells for the samples frozen at -20 and -50°C were 20-30 and 500-1500 cells/mm², respectively, in the cross sections of the sintered bodies. The resulting porous cordierite with a total porosity of 87% showed a compressive strength of 4 MPa; this was thought to be due to the tight packing during freezing. The porosity, number of cells and strength were significantly higher than the reported values for other porous cordierite ceramics.