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.

Cylindrical SiOC foam filaments with a radial gradient in pore cell size were processed by continuous extrusion foaming of a methyl polysilsesquioxane. Upon leaving the extrusion nozzle foaming was initiated by pressure release which caused precipitation of supersaturated carbon dioxide from the polymer filament. Rapid cooling of the thin filaments generates a radial gradient of melt viscosity which gives rise for formation of closed cell morphology of isotropic pore cells in the core (diameter < 200 µm) and non‐isotropic pore cells near the sur‐face (shell; <20 µm). After pyrolysis at temperatures ranging from 800 to 1400 °C the stabilized polymer gradient foams were converted into closed cell SiOC ceramic gradient foams. XRD reveals the SiOC residue to be amorphous up to 1200 °C whereas crystallization of ß‐SiC was observed at 1400 °C. A superior compressive strength of 9 MPa and a Young´s modulus of 7 GPa at a relative density of 0.18 were measured at an optimum pyrolysis temperature of 1000 °C.

Due to their high hardness, high temperature stability, and high chemical stability, ceramic materials have significant uses and potential in existing and emerging sustainable technologies. In this paper, we provide a thorough overview of ceramics in a variety of sustainable applications. This is followed by a detailed discussion of an emerging process to make ceramics called polymer (or precursor)-derived ceramics. It is shown that due to the versatility of this process in making a wide range of shapes-fibers, coatings, and porous ceramics, this is an attractive route to make ceramics that will be a critical element in the next generation of sustainable technologies.