CERAMICS INTERNATIONAL Available online at www.sciencedirect.com Ceramics International 39 (2013) 5327–5333 Characterization of textured ceramics containing mullite from phyllosilicates K. Boussois a , S. Deniel a , N. Tessier-Doyen a , D. Chateigner b , C. Dublanche-Tixier c , P. Blanchart a,c,n a GEMH, ENSCI, 12 rue Atlantis, 87068 Limoges, France b CRISMAT-ENSICAEN, Universite´ de Caen Basse Normandie 14050, Caen, France c SPCTS, ENSIL, Universite´ de Limoges, 87068 Limoges, France Received 18 September 2012; received in revised form 11 December 2012; accepted 12 December 2012 Available online 1 January 2013 Abstract Organized ceramics are obtained from kaolinite and muscovite suspensions and shaped by aqueous tape casting or centrifugation. These processes favor the preferential orientation of particles in the powder compact. After sintering at 1400 1C, this study analyzed sample microstructures using QTA to determine the degree of the mullite orientation. The analyses revealed two main texture components, a planar texture along the c-axis of the mullite and a preferred orientation along the a-axis, which were aligned parallel and perpendicular to the casting plane, respectively. The important role of processing parameters in the organization degree of the mullite was apparent during the study. The elastic properties at different measurement scales were obtained using US echography and nanoindentation and were closely related to the organization degree of the mullite crystals obtained from the QTA analyses that were consistent with the development of an interconnected mullite network. The Young’s moduli due to the nanoindentations were also determined parallel and perpendicular to the layers, and indicated the samples’ anisotropic behavior. Both the Young’s modulus and the anisotropy of the Young’s modulus were correlated with the texture index. In particular, the anisotropy of the Young’s moduli was linearly related to the overall texture index, highlighting the microstructures’ anisotropic nature. & 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Keywords: A. Tape casting; C. Mechanical properties; D. Mullite; Pole figures (QTA) 1. Introduction Ceramic materials with organized microstructures can be obtained from powder compacts with anisotropic grains using specific shaping processes for tape casting and centrifugation. Tape casting [1,2] consists of spreading a suspension on a fixed support composed of a flat piece of glass coated with a Mylar film and is also called Doctor Blading. This forming method has the advantage of producing laminated green tapes with uniform thickness, density and surface flatness. Tape-casting is used extensively for the manufac- ture of substrates and multilayer structures, and uses a mixture of powders, solvents and various additives as dispersants and plasticizers. Non-aqueous organic solvents are commonly used because they improve the rheology of highly concentrated slurries and accelerate the drying process of green tapes. However, slurry formulations that contain water have also been successfully used with different powder types [3,4]. The slurry formulation requires water-soluble binders, plasticizers and dispersants in amounts that are highly dependent on powder type, granulometry and relative concentration. Because lamina- tion always occurs during tape casting, it induces the preferential orientation of elongated and sheet particles, as phyllosilicates, in the direction plane to the tape direction. Centrifugation can also be used to obtain oriented powder compacts from aqueous suspensions of various anisotropic grains as phyllosilicates [5] . During the centrifugation process, www.elsevier.com/locate/ceramint 0272-8842/$ - see front matter & 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved. http://dx.doi.org/10.1016/j.ceramint.2012.12.038 n Corresponding author at: GEMH, ENSCI, 12 rue Atlantis, 87068 Limoges, France. Tel.: þ 33 87 502 300. E-mail address: philippe.blanchart@unilim.fr (P. Blanchart).