Design and processing of SiOC/SiC/Si3N4/C ceramics with hierarchical porosity and non-oxide nanostructures

An integral study on the development and characterization of porous SiOC/SiC/Si3N4/C-based ceramic bodies was conducted using a less-explored approach, which is based on the direct consolidation of previously unstudied composite systems (methacryloxypropyl silsesquioxane/sucrose/prepyrolyzed powder), burn-out, and N2 pyrolysis (1300–1400 °C). Their textural, physicochemical, and microstructural properties depended on the initial system composition and pyrolysis temperature; the latter was also decisive in the materials' oxidative stability. At the highest pyrolysis temperature, SiC, mainly in the form of whiskers, and Si3N4 formed, the amount of SiOC decreased, Si2N2O crystallized, and nanocrystalline graphite-type carbon underwent graphitization. The final bodies exhibited macro- and mesopores, with micropores present only in those pyrolyzed at 1300 °C. This latter material presented the highest specific surface area, making it a potential candidate for catalysis in non-oxidizing environments at high temperatures or in oxidizing conditions at lower temperatures. Meanwhile, the material developed at 1400 °C offered high-temperature oxidative stability.