Reticulated porous ceramics (RPCs) have found a wide range of applications real industry, and one of the most used techniques for their manufacturing is the polymer replica method developed by Schwartzwalder and Somers. For the mostly applied polymeric templates, due to their burn-out at high temperatures, triangular voids remain within the struts of the final RPCs, degrading their mechanical strength and stability. In this study we propose using open cellular metallic foams with solid struts as templates to fabricate RPCs.
The metallic templates used in our study were reticulated aluminum foams. A dip coating technique was employed to coat the Al foams with an Al2O3 slurry, and then the coated foams were subjected to high temperature processing with varied temperatures and dwelling periods. To mend the surface cracks and cavities in the struts, the as-prepared foams were also processed by recoating and infiltration. All the foams were characterized with respect to their micro- and macrostructure, geometric characteristics and compression strength.
By this means, novel Al/Al2O3 composite foams with solid struts, avoiding the triangular voids as found in conventional RPCs, were obtained. The aluminum templates were only partially oxidized to alumina, thus the struts possessed an interesting ternary-layered structure which consisted of an inner aluminum core, a middle layer of oxidized aluminum and the outside layer of Al2O3 coating. Due to the existence of an aluminum core the composite foams displayed much better ductility compared to traditional RPCs. Their compression strength ranged between 0.26 MPa and 0.60 MPa for varied processing temperatures, and their porosities were around 85%. Some surface cracks and inside cavities occurred in the struts, which were mended by further recoating and infiltration treatments. The compression strength was increased to 1.32 MPa by recoating and 1.24 MPa by infiltration, respectively.