Effect of cooling rate on the microstructure and porosity of alumina produced by freeze casting

Abstract

Freeze casting is a well-known shaping technique for the production of materials with directional porosity. One of the major problems is the difficulty to control the cooling rate, thus leading to gradients in pore size and homogeneity. This work deals with the manufacture of alumina ceramics with directional porosity by freeze casting of aqueous suspensions. An experimental set-up was prepared in order to apply different cooling rates. Freeze casting tests were performed with an aqueous alumina suspension after optimization of its rheological behavior. The porosity and microstructural features of the sintered bodies produced under different experimental conditions were studied and analyzed. It was concluded that the cooling rate influences the microstructure while the final temperature has a much lower influence. In addition, microstructural analysis showed that there was a gradient in the directionality of the pores, being lower at the bottom and the top and higher in the central region of the specimens.