Preparation of unidirectional porous AlN ceramics via the combination of freeze casting and combustion synthesis

Unidirectional porous AlN ceramics (UP-AlNs) have attracted great attention for their wide applications in catalyst supports, filters and composite reinforcements. However, traditional fabrication processes usually require high temperature and long production cycle. Herein, UP-AlNs were successfully fabricated via the combination of tertiary butyl alcohol (TBA)-based freeze casting and combustion synthesis route using Al and AlN powders as raw materials. The microstructure, open porosity, thermal conductivity and compressive strength of UP-AlNs can be manipulated by synergistically regulating the AlN diluent content and Al/AlN solid loading of the freezing slurries. The optimal UP-AlNs exhibited controllable structure wavelength (λ) and open porosity in a wide range of 21.1-47.1 μm and 54.2-86.0%, respectively. In addition, the corresponding products also possessed anisotropic thermal conductivity and compressive strength. This novel route for the fabrication of UP-AlNs has the advantages of low cost, energy-saving and high efficiency, which shows significant promise for industrial applications.