Ice templating of ZrB2-based ceramics

Porous architectures of ZrB2 ceramics and ZrB2-SiC composite were prepared, where the pores are the replica of the ice crystals developed by freeze casting. The effects of solid content, suspension stabilization and cold transmission depending on mold type were studied since micro and macrostructure and, hence, the properties of the sintered body are determined by controlling the growth direction of the ice crystals during freezing. Monophasic ZrB2 powders suspensions produced porous architectures with main unidirectional anisotropic pores interconnected by diffuse globular-isotropic pores. Improved mechanical performance, due to the formation of thinner and homogenously distributed ceramic lamellae, were obtained changing the process parameters. With ZrB2-SiC composite suspensions, the ice networking resulted in macro-pores arranged into dendritic distributions which were randomly distributed in the samples or in porous domains of elongated voids with irregular boundary. Samples showed intrinsic spectral selectivity, which can be interesting for high-temperature solar absorber applications.