Capillary rise properties of porous mullite ceramics prepared by an extrusion method using organic fibers as the pore former |
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Authors: | Kiyoshi Okada Shuhei Uchiyama Toshihiro Isobe Yoshikazu Kameshima Akira Nakajima Taisuke Kurata |
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Affiliation: | 1. Department of Metallurgy and Ceramics Science, Tokyo Institute of Technology, 2-12-1 O-okayama, Meguro, Tokyo 152-8552, Japan;2. Materials and Structures Laboratory, Tokyo Institute of Technology, 4259 Nagatsuta, Midori, Yokohama, Kanagawa 226-8503, Japan;3. Kurata Refractory Co. Ltd., Hirono, Futaba, Fukushima 979-0402, Japan;1. School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong University, Beijing 100044, PR China;2. State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and Engineering, Tsinghua University, Beijing 100084, PR China;3. Department of Materials Science and Engineering, Advanced Materials Processing and Analysis Center, University of Central Florida, Orlando, FL 32816, USA;1. University of Erlangen-Nuremberg, Department of Materials Science, Glass and Ceramics, 91058 Erlangen, Germany;2. Brandenburg University of Technology, Department of Joining and Welding Technology, 03046 Cottbus, Germany;3. Forschungszentrum Jülich GmbH, Institute of Energy and Climate Research, IEK-2, 52425 Jülich, Germany |
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Abstract: | Porous mullite ceramics with unidirectionally oriented pores were prepared by an extrusion method to investigate their capillary rise properties. Rayon fibers 16.5 μm in diameter and 800 μm long were used as the pore formers by kneading with alumina powder, kaolin clay, China earthen clay and binder with varying Fe2O3 contents of 0, 5 and 7 mass%. The resulting pastes were extruded into cylindrical tubes (outer diameter (OD) 30–50 mm and inner diameter (ID) 20–30 mm), dried at room temperature and fired at 1500 °C for 4 h. The bulk densities of the resulting porous ceramics ranged from 1.31 to 1.67 g/cm3, with apparent porosities of 43.2–59.3%. The pore size distributions measured by Hg porosimetry showed a sharp peak at 10.0 μm in the sample without Fe2O3 and at 15.6 μm in the samples containing Fe2O3; these pores, which arose from the burnt-out rayon fibers, corresponded to total pore volumes ranging from 0.24 to 0.34 ml/g. SEM showed a microstructure consisting of unidirectionally oriented pores in a porous mullite matrix. Prismatic mullite crystals were well developed on the surfaces of the pore walls owing to the liquid phase formed by the Fe2O3 component added to color the samples. The bending strengths of the tubular samples ranged from 15.6 to 26.3 MPa. The height of capillary rise, measured under controlled relative humidities (RH) of 50, 65 and 85%, was greater in the ceramics containing Fe2O3 than in those without Fe2O3, especially in the thinner samples. The maximum capillary rise reached about 1300 mm, much higher than previously reported. This excellent capillary rise ability is thought to be due to the controlled pore size, pore distribution and pore orientation in these porous mullite ceramics. |
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