Contents lists available at ScienceDirect Ceramics International journal homepage: www.elsevier.com/locate/ceramint Macroporous alumina structures tailored by freeze-casting using naphthalene–camphor as freezing vehicle Lucas D. Lacerda a , Douglas F. Souza b , Eduardo H.M. Nunes c , Manuel Houmard d, ⁎ a Department of Mechanical Engineering, Federal University of Minas Gerais - UFMG, Avenida Presidente Antônio Carlos, 6627, Campus UFMG, Escola de Engenharia, Bloco 1, Belo Horizonte, MG CEP: 31270-901, Brazil b National Institute of Industrial Property – INPI, Rua Mayrink Veiga, 9 - Centro, Rio de Janeiro, CEP: 20090-910, Brazil c Department of Metallurgical and Materials Engineering, Federal University of Minas Gerais - UFMG, Avenida Presidente Antônio Carlos, 6627, Campus UFMG, Escola de Engenharia, Bloco 2, Belo Horizonte, MG CEP: 31270-901, Brazil d Department of Materials Engineering and Civil Construction, Federal University of Minas Gerais - UFMG, Avenida Presidente Antônio Carlos, 6627, Campus UFMG, Escola de Engenharia, Bloco 1, Belo Horizonte, MG CEP: 31270-901, Brazil ARTICLE INFO Keywords: A. Freeze-casting B. Porosity C. Mechanical properties D. Al 2 O 3 E. Macroporous structures ABSTRACT Freeze-casting is a promising technique for fabricating macroporous ceramics because it is an environmentally friendly, cost effective, and easy scale-up method. Several freezing vehicles have been used in freeze-casting, including water, camphene, tert-butyl alcohol, urea, and naphthalene-camphor (Naph-Camp). This work focuses on the preparation of freeze-cast alumina samples using different Naph-Camp compositions as freezing vehicle, alumina loading ranging from 20 to 40 vol% and various freezing conditions. It was observed that macroporous materials with different pore structures and mechanical behaviors can be obtained by changing the Naph-Camp solvent composition. Moreover, the freezing route also showed a great effect on these properties, besides al- lowing the preparation of samples with oriented pores. These are important findings because naphthalene and camphor are widely available, have low toxicity, and show an easier sublimation than water, which has been commonly used as the freezing vehicle in many works. The range of pore structures and mechanical strengths obtained in this study demonstrates the versatility of the processing route used herein, which could be used to obtain samples for several applications, including catalysis, fluids filtration, and bioengineering. This study is supported by a series of experimental characterizations, including optical microscopy, scanning electron mi- croscopy, Archimedes measurements, and cold crushing tests. 1. Introduction Ceramic materials with tailored macroporous structures have been used in several applications, including biomaterials, catalysis, phase separation, and thermal insulation [1–5]. It has been reported that the wide use of these materials is strongly associated with properties arising from a controlled substitution of a solid phase by pores [6]. Such properties may include high specific surface area, low density, low thermal conductivity, and high anisotropic mechanical strength. Among the different techniques used to produce macroporous ceramics, the freeze-casting method is a promising approach because it is an environmentally friendly, cost effective, and easy scale-up method [7]. In addition, freeze-cast materials usually show a highly-interconnected pore structure, which gives rise to solids with improved mass transport capacities [8]. A range of freezing vehicles has been used in freeze-casting, including water [9,10], camphene [11,12], tert-butyl alcohol [8,13], urea [14], and naphthalene-camphor (Naph-Camp) [15]. Water is ob- viously an interesting solvent since it is cost effective, versatile, and non-toxic [16]. However, water solidification is carried out at tem- peratures below 0 °C and its sublimation is performed under reduced pressures, which increases the process complexity due to the need of specific equipments. In agreement to a wide literature in the area, camphene is also an interesting option to be used as solvent for fabri- cating macroporous materials by freeze-casting due to is low-toxicity and easy sublimation under ambient conditions [17,18]. For these reasons, camphene have been used to produce macroporous structures for biomedical application for instance [19]. Nevertheless, since cam- phene has a dendritic growth during its solidification [20], the porous structures obtained with this solvent often show dead-ended pores which could decrease the material performance in some applications. To reduce the presence of such inadequate pores, Liu et al. [21] https://doi.org/10.1016/j.ceramint.2018.06.036 Received 25 April 2018; Received in revised form 4 June 2018; Accepted 5 June 2018 ⁎ Corresponding author. E-mail address: mhoumard@ufmg.br (M. Houmard). Ceramics International xxx (xxxx) xxx–xxx 0272-8842/ © 2018 Elsevier Ltd and Techna Group S.r.l. All rights reserved. Please cite this article as: Lacerda, L.D., Ceramics International (2018), https://doi.org/10.1016/j.ceramint.2018.06.036