Macroporous alumina structures tailored by freeze-casting using naphthalene-camphor as freezing vehicle

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 allowing 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 microscopy, Archimedes measurements, and cold crushing tests.