Available online at www.sciencedirect.com Journal of the European Ceramic Society 30 (2010) 635–639 Synthesis and mechanical properties of porous alumina from anisotropic alumina particles S. Hashimoto a,∗ , S. Horita a , Y. Ito a , H. Hirano b , S. Honda a , Y. Iwamoto a a Department of Environmental and Engineering Materials, Nagoya Institute of Technology, Gokiso-cho, Showa-ku, Nagoya-shi 466-8555, Japan b Towa Refractory Engineering, Co., Ltd., Research and Development Division, 21-1 Nakaedo, Kani-shi 509-0202, Japan Received 10 June 2009; received in revised form 2 September 2009; accepted 16 September 2009 Available online 13 October 2009 Abstract A porous alumina body was synthesized from anisotropic alumina particles (platelets). The uniaxial pressure in fabricating the green compact body had an influence on the relative density of the alumina body after heating. When green compacts, which had been uniaxially pressed at 1 and 3 MPa, were heated at 1400 ◦ C for 1 h, the relative densities of the resulting alumina bodies were 25.0% and 35.5%, respectively. The compressive strength of compacts that were uniaxially pressed at 1 and 3 MPa were 0.8 and 4.3 MPa, respectively. In an attempt to increase the compressive strength of these porous alumina bodies, aluminum nitrate and magnesium nitrate solution treatments were performed, followed by reheating to 1400 ◦ C for 1 h. When a 0.5 mol/l aluminum nitrate solution was used, the compressive strength of the porous alumina body uniaxially pressed at 1 MPa changed from 0.8 MPa (without solution treatment) to 1.5 MPa. Furthermore, when 0.1 mol/l magnesium nitrate solution was used, the compressive strength of the porous alumina increased to 1.7 MPa. Thus, solution treatment of the porous alumina body had a strong positive effect on its mechanical strength. © 2009 Elsevier Ltd. All rights reserved. Keywords: A. Powder-solid state reaction; B. Platelets; C. Strength; D. Al 2 O 3 ; Insurators 1. Introduction Porous ceramics have many desirable properties such as their light weight, high chemical stability, and low thermal conduc- tivity, so that their application is extending into various fields, such as environmental, energy, biotechnology, and others. Sev- eral methods for the fabrication of porous alumina ceramics have been studied for a variety of applications. 1–5 Recently, to enable energy savings, porous alumina ceramics have been proposed for use as high temperature insulators, for instance, as a porous clinker in steel refractories. Such refractories are able to easily maintain a high temperature in the furnace, which leads to lowered energy cost of making steel. A castable refrac- tory requires alumina porous clinkers with approximately 75% porosity (1.0 × 10 3 kg/m 3 ), since castable materials are mixed with water, and then finish forming inside the steel furnace. In addition, the porous clinker requires some mechanical strength. ∗ Corresponding author. E-mail address: hasimoto.shinobu@nitech.ac.jp (S. Hashimoto). In order to obtain a uniform porous structure, high porosity, and sufficient mechanical strength, uniform anisotropic alumina par- ticles (platelet in shape) should be suitable. Until now, scientific reports of fabrication methods based on alumina platelets have been limited. 6–8 However, the authors have developed a novel synthetic method for alumina platelet particles. 9,10 These new alumina platelet particles were employed for the fabrication of novel porous alumina ceramics. In this study, a porous alumina body composed of anisotropic alumina particles (platelets) was fabricated using a simple heat- ing method. Initially, the effect of varying the uniaxial pressure applied to the green compact body on the porosity and mechani- cal properties of the resulting porous alumina was studied. Since it is very difficult to fabricate porous bodies from only alumina platelet particles, fine alumina particles were added as a sin- tering additive and corn starch was added as a pore foaming agent. Furthermore, in order to strengthen the porous alumina, an aluminum nitrate solution or magnesium nitrate solution treatment was performed on the resulting porous alumina body. The strengthening mechanism of the porous alumina will be discussed in a later section. 0955-2219/$ – see front matter © 2009 Elsevier Ltd. All rights reserved. doi:10.1016/j.jeurceramsoc.2009.09.018