Tubular ceramic structures from polymer precursors with controlled porosity, strength, and permeability characteristics

A processing technique for the preparation of porous, silicon carbonitride-based ceramics in tubular geometry derived from a liquid polysilazane precursor is presented. After casting of polysilazane/polymer-microbead dispersions, cross-linking, and subsequent pyrolytic conversion and selective removal of polymer templates, specimens with an inner and outer diameter of 6 and 10 mm, respectively, and a length of up to 65 mm were obtained. Porosity was controlled by sacrificial template content and reached values up to 48% after pyrolytic conversion, at average pore opening radii of 1 µm. The tubular specimens exhibited diametral compression strengths (C-ring test) between 24 ± 6 and 36 ± 4 MPa. Darcian permeability constants of up to 1.7·10−14 m2 were found by gas permeability testing. The results demonstrate that this methodology facilitates the straightforward generation of complex-shaped porous specimens, further allowing for a control of strength and permeability in a specific range. Potential applications for the tubular, porous structures developed can be anticipated in the fields of separation or catalysis.