Optimization of the ceramization process for the production of three-dimensional biomorphic porous SiC ceramics by chemical vapor infiltration (CVI)

The ceramization process for the preparation of three-dimensional (3D) biomorphic porous SiC ceramics by chemical vapor infiltration (CVI) with methyltrichlorosilane/hydrogen mixture has been optimized in this work. As a first step, two alternative ceramization routes have been compared with each other with regard to composition, morphology and bending strength of the resulting ceramics using flat samples. Optimal ceramization route was found to be a three-step process including carbonization of the paper preforms, followed by chemical vapor infiltration with stoichiometric SiC layers and a final oxidation step, in which the residual carbon from the template (Cb) is burnt out of the ceramics. Based on these results 3D honeycomb structures have been ceramized. Prior to these experiments, a computational fluid dynamics simulation of the gas flow in the reactor and through the honeycomb structure has been performed with the software STAR-CD. As a result, homogeneously infiltrated three-dimensional structured SiC ceramics could be produced.