Porous alumina ceramics by spray-pyrolyzed powder from aluminum sulfate and aluminum nitrate solutions
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Keiji Daimon Department of Materials Science and Engineering, Nagoya Institute of Technology, Gokiso, Showa, Nagoya, Aichi 466, Japan
Nozomu Otsuka Department of Materials, Nishi-Tokyo University, Uenohara, Kitatsuru, Yamanashi 409-01, Japan (Received 24 November 1993; accepted 7 February 1994)
Porous a-alumina ceramics were prepared using the spray-pyrolyzed powder from aluminum nitrate solution and aluminum sulfate solution. Porosity and pore size distribution of the samples were examined with respect to the forming pressure and firing temperature. The porosity obtained changed from around 80% in the green compacts to 60-70% in the fired bodies fired at 1500 °C. The porosity of 30-40% remained even by firing at 1700 °C. Although there was no significant difference in the porosity of the fired bodies prepared from the sulfate and nitrate solutions, the fired bodies prepared from the nitrate solution showed apparently larger pore size than those from the sulfate solution. Fired bodies with an average pore radius from 0.2 to 0.8 fim can be prepared by this method. The four-point bending strength of the fired bodies, which had a porosity of 57% and an average pore radius of 0.23 fim, was 35 MPa.
I. INTRODUCTION Spray pyrolysis has been widely studied to prepare fine and homogeneous multicomponent powder. 1 ^ In this method, powder is obtained by atomizing a precursor solution into a reaction chamber held at elevated temperatures. The small droplets are rapidly dried and reacted to form a complex compound instantly. Since the evaporation of solvent is very rapid, the synthesized powder is apt to form a hollow sphere around several fim to several tens of fim in diameter. It is, therefore, necessary to break down the particles when they are used for the raw materials of dense ceramics. On the other hand, hollow particles are considered to be suitable for raw materials of porous ceramics rather than dense ceramics. Kanzaki et al.5 reported porous spinel (MgAl 2 O 4 ) ceramics prepared from the spray-pyrolyzed powder. They were easily successful in preparing porous ceramics with 50-80% porosity and average pore radius of around 0.1 fim. Spray-pyrolyzed powder is, therefore, suitable for the raw materials of porous ceramics. Various porous materials are used in a variety of fields and are mainly made by polymers and ceramics. Porous ceramics have the following advantages for porous polymers: (i) high heat resistance, (ii) high a 'Author
to whom correspondence should be addressed. address: Tokyo Gas Co., 1-16-25 Shibaura, Minato, Tokyo 105, Japan.
b) Present
J. Mater. Res., Vol. 9, No. 7, Jul 1994
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chemical resistance, and (iii) high mechanical strength and hardness. Therefore, porous ceramics are used for various applications such as insulators, filters, separators, supports for catalyst and bioreactors, sensors, ion exchangers, and so on. Among various ceramics, alumina is considered to be the best candidate to fulfill the above-mentioned points. Therefore, por
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