JOURNAL OF MATERIALS SCIENCE 40 (2 0 0 5 ) 2903 – 2909 The effect of polyelectrolyte on fabrication of macroporous ZrO 2 ceramics YU JIA National Institute of Advanced Industrial Science and Technology (AIST), Anagahora 2266-98, Shimoshidami, Moriyama-ku, Nagoya 463-8560, Japan CIHANGIR DURAN National Institute of Advanced Industrial Science and Technology (AIST), Anagahora 2266-98, Shimoshidami, Moriyama-ku, Nagoya 463-8560, Japan; Gebze Institute of Technology, Department of Materials Science and Engineering, P.K. 141, 41400, Gebze-Kocaeli, Turkey YUJI HOTTA ∗ , KIMIYASU SATO, KOJI WATARI National Institute of Advanced Industrial Science and Technology (AIST), Anagahora 2266-98, Shimoshidami, Moriyama-ku, Nagoya 463-8560, Japan E-mail: y-hotta@aist.go.jp The effect of polyethylenimine (PEI) on preparing macroporous ZrO 2 materials via heterocoagulation coating process was investigated, using ZrO 2 nanoparticles as the building materials and polystyrene spheres as the organic templates. When PEI was applied to modify the surface charge of ZrO 2 nanoparticles, it was found that 40–50% of initial PEI amount remained excess in the suspensions. Adsorption of excess PEI on the surface of polystyrene spheres resulted in partial coating of the polystyrene spheres by ZrO 2 nanoparticles at 1 wt% PEI and even no coating at 3 wt% PEI. Microstructure studies revealed that ZrO 2 ceramics prepared without using PEI had quite ordered macropores, while the ZrO 2 framework was partially collapsed at 1 wt% PEI and disordered macropores were observed at 3 wt% PEI. C  2005 Springer Science + Business Media, Inc. 1. Introduction Well-ordered macroporous materials with three- dimensional periodicity are of significant interest in the last decades due to their potential applications in photonic crystals, catalysts, biomaterials and so on [1– 5]. At present, various methods have been developed for preparing well-ordered macroporous materials. A colloidal crystal templating method using close-packed arrays of monodispersed template spheres (polystyrene or silica) was commonly applied to prepare three dimensionally ordered macroporous (3-DOM) mate- rials such as silica [6, 7], metals [8–10], metal ox- ides [11–13], polymers [14] and carbon [15]. Never- theless, control of wall thickness between pores was found to be limited. In addition to the crystal tem- plating method, ordered macroporous materials with a controlled pore size were fabricated by a colloidal templating method using precoated templates [16– 18]. A heterocoagulation method has also been ap- plied to prepare well-ordered macroporous materi- als by utilizing commercial ceramic nanoparticles as building blocks [19–21]. The critical problem in this method is to prepare core and shell particles that are oppositely charged at the same pH range. There- ∗ Author to whom all correspondence should be addressed. fore, polyelectrolyte reagents have been frequently ap- plied in order to modify the particle surface charge [19, 22–24]. In this study, the effect of polyethylenimine (PEI) on the fabrication of macroporous ZrO 2 ceramics was investigated. It was aimed to understand the role of PEI on heterocoagulation process between polystyrene spheres and nano ZrO 2 powders in aqueous suspen- sions. Characterization of the suspensions was carried out by zeta potential, particle size measurement and sedimentation kinetics. Green samples, prepared by slip casting, were used to analyze the microstructure of the macroporous materials sintered at 1000 ◦ C as a function of PEI content. 2. Experimental procedure In the preparation of macroporous ZrO 2 materials, 3 mol% yttria-stabilized nano ZrO 2 powders (Aldrich, USA) with an average particle size of about 50 to 75 nm and specific surface area of 37.9 m 2 /g were used as building blocks. As-received suspension of surfactant-free polystyrene spheres (PS) (8.2 wt%, av- erage particle size of 1 µm, Interfacial Dynamics Corp., 0022–2461 C  2005 Springer Science + Business Media, Inc. 2903