Processing of Ceramic Foams with Hierarchical Cell Structure

Abstract Silicon carbide‐based cellular ceramics characterized by a hierarchical pore structure were processed. An open‐cellular PU foam template with a mean cell density of 10 pores per inch (ppi), equivalent to a cell diameter of 4 mm and a strut thickness of 250 µm, was coated with a primary SiC slurry. Cross‐linking of a polysiloxane binder at 190 h resulted in a SiC filled reticulated thermoset foam (first generation). Subsequently, this matrix foam was infiltrated with a second slurry of slightly different polysiloxane composition which upon heating to 290 °C caused bubble nucleation and formation of a second generation foam filling the cell space in the matrix foam skeleton. After pyrolysis at 1000 °C a SiC/SiOC reaction bonded composite foam with a hierarchical cell structure and a fractional density of 0.31 was obtained. SEM and X‐ray µ‐CT analyses confirm both generations of matrix as well as infiltrated foam to be open cellular but with a pronounced difference in cell size (matrix foam cell size 2.5 mm versus infiltrated foam cell size 0.29 mm). While the matrix foam skeleton provides control of macroscopic shape as well as density distribution in the component, single‐ or multistep foam infiltration may offer a high potential for improving the mechanical properties of hierarchical cellular materials. Thus, hierarchical structure formation offers a high potential to fabricate low density cellular ceramics which might be of interest for lightweight design of novel engineering materials.