Research paper Extrusion of ceramic emulsions: Preparation and characterization of cellular ceramics C. Freitas b , N. Vitorino a, ⁎, M.J. Ribeiro b , J.C.C. Abrantes a,b , J.R. Frade a a CICECO-Aveiro Institute of Materials, Department of Materials and Ceramic Engineering, University of Aveiro, 3810-193 Aveiro, Portugal b UIDM, ESTG, Polytechnic Institute of Viana do Castelo, 4900-348 Viana do Castelo, Portugal abstract article info Article history: Received 30 September 2014 Received in revised form 11 March 2015 Accepted 13 March 2015 Available online xxxx Keywords: Ceramic emulsions Extrusion Porous ceramics Emulsions characterization Recently, much effort has been given to development and/or optimization of porous materials with requirements for intended applications in catalysis, filtration, isolation, etc. In this context, this paper presents processing con- ditions and the correspondent characterization of cellular ceramics processed by extrusion of ceramic emulsions, obtained by emulsification of red clay, kaolin and alumina suspensions, after sintering at different temperatures. The emulsification of the ceramic suspension in paraffin with a melting point higher than room temperature is the key for the success of this processing method due to the freezing of the organic droplets allowing good sta- bility of matrix during the extrusion process. Experimental results show good microstructural stability, yielding cellular ceramics with mechanical strength up to 30 MPa, permeability up to 3 × 10 -4 ms -1 , and thermal con- ductivity lower than 0.25 W m -1 K -1 , framed with mentioned applications. © 2015 Elsevier B.V. All rights reserved. 1. Introduction Cellular ceramics have been extensively studied due to their specific properties such as high permeability, low relative density, high specific area, low thermal conductivity and high thermal shock resistance. These properties are strongly dependent on microstructural features, namely porosity, shape, average cell size and size distribution, wall thickness and also connectivity between the cells (Acchar et al., 2008; Vitorino et al., 2013a), Table 1. According to their properties, cellular ceramics can be framed with specific applications like filters for hot liquids or gases, supports for catalysts, bioreactors, biomaterials, porous supports for batteries, fuel cells, etc. (Han et al., 2003a, 2003b; Vitorino et al., 2013a; Sanches et al., 2014). The diversity of microstructural features is highly dependent on the preparation conditions used for cellular ceramics production (Studart et al., 2006). In this context, several strategies were proposed to prepare these materials, including: i) replication (Acchar et al., 2008; Nor et al., 2008), gel casting (Sepulveda and Binner, 1999; Bartuli et al., 2009; Luyten et al., 2009), emulsification of ceramics suspensions with vola- tile alkanes (Barg et al., 2009) or in melted paraffin(Vitorino et al., 2013a; Sanches et al., 2014), and correspondent processing methods such as tape casting, slip casting, gel casting, spin coating, extrusion or even screen printing (Isobe et al., 2006; Sarkar et al., 2012; Sanches et al., 2014). Extrusion is a unitary operation widely used in industry (ce- ramics, metal, food, etc.), allowing large scale production of regular shapes with constant cross section such as tubes or rods, bricks, etc. (Ribeiro et al., 2005). However, the success of this operation is dependent on the plasticity of the material to be extruded, i.e. the material ability to be deformed without rupture, through the appli- cation of stress, and to retain the deformation, when stress is re- moved or reduced (Ribeiro et al., 2006). The role of plasticity on extrusion is well known (Andrade et al., 2011) and this property may be assessed by stress-deformation curves obtained by compres- sion of extruded bodies. This method allows one to know, for each paste with a specific humidity, the stress required for plastic defor- mation and the amplitude of the plastic zone, i.e., the maximum deformation without cracking or other macroscopic defects in the extruded bodies (Vitorino et al., 2014, 2015). In a recent work one evaluated the plastic behaviour of ceramic emulsions prepared by emulsification of ceramic suspensions in melted paraffin, in order to obtain some insights for upscaling, and concluded that the combination of emulsification of ceramic suspensions in melted paraffin with extrusion is a suitable strategy to produce cellular porous ceramic materials in a large scale with constant cross section (Vitorino et al., 2014). The extrudability of ceramic emulsions has already been assessed in previous works. Nevertheless, some physical properties are mandatory Applied Clay Science 109–110 (2015) 15–21 ⁎ Corresponding author. Tel.: +351 258 819 700; fax: +351 258 827 636. E-mail address: nuno.vitorino@ua.pt (N. Vitorino). http://dx.doi.org/10.1016/j.clay.2015.03.011 0169-1317/© 2015 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Applied Clay Science journal homepage: www.elsevier.com/locate/clay