SiCO ceramic microspheres produced by emulsion processing and pyrolysis of polysiloxanes of various structures

Crack-free silicon oxycarbide microspheres were synthesized from precursors obtained by a one-pot aqueous emulsion-process of modified polyhydromethylsiloxane. The process involved cross-linking by hydrosilylation and the advanced hydrolysis of polyhydromethylsiloxane SiH groups to SiOH. These species then participate in SiOH+SiH condensation, enhancing the cross-linking. The microspheres were additionally modified by SiH group-substitution in the initial polymer and by using various cross-linkers. The precursor powder particle structure was also modified by varying the stirring rate during emulsification. The modified preceramic microspheres, with average diameters from 7.6 to 56 µm, were subjected to pyrolytic processes at various temperatures. The chemical composition of the pyrolyzed microspheres and their precursors was studied by 29Si and 13C MAS NMR, FTIR spectroscopy, and elemental analysis. The structures of the microspheres were examined by SEM. Selected samples were also investigated by XRD and Raman spectroscopy. All of the synthesized preceramic microspheres retained their regular spherical shapes during pyrolysis at temperatures of up to 1200 °C. Heating at 1000 °C and 1200 °C yielded amorphous silicon oxycarbide ceramic materials with segregated free carbon domains. The chemical structure and morphology of the obtained ceramic microspheres were significantly influenced by the modification of the preceramic materials.