Synthesis and structural characterization of carbon-rich SiCxOy derived from a Ni-containing hybrid polymer

Carbon-rich silicon oxycarbide ceramics were obtained by controlled pyrolysis at 950, 1300 and 1500 C from hybrid polymeric precursors based on poly(methylsiloxane) and divinylbenzene with different molar ratios, in the presence or absence of nickel acetate. By increasing the pyrolysis temperature, changes in the local molecular structure were observed by 29Si NMR, with the segregation of thermodynamically stable SiO2 and SiC phases, in addition to the formation of graphitic carbon nanoclusters. Ceramics without Ni were amorphous at 950 C, while those obtained at 1300 C showed the presence of a beta-SiC phase. The presence of Ni in the polymeric precursor induced the formation of beta-SiC, cristobalite silica, graphitic carbon, metallic Ni, NiO and Ni2Si, and also reflected in denser materials. In general, the resulting ceramics without Ni did not present measurable porosity, whereas Ni-containing ceramics at 1500 C showed behaviour typical of mesoporous materials. 50 refs.