Influence of multiwall carbon nanotubes on the structural and morphological features of Si–C–O ceramics derived from a hybrid polymeric precursor

This study describes the effect of multiwall carbon nanotubes, MWCNT, as an additional C-source, on the structural and morphological features of silicon oxycarbide ceramics obtained by different heat treatment times of a hybrid polymeric precursor at 1500 °C under an Ar atmosphere. The precursor was prepared by a hydrosilylation reaction from poly(methylsiloxane) and divinylbenzene. The presence of MWCNT promoted a more effective crystallization of the SiC and c-SiO2 phases in the resulting ceramics, in comparison with those without MWCNT. The heat treatment time at 1500 °C also affects the crystallization of the ceramic product. In addition, an increase of the defect density in the Csp2 sheets of the Cfree dispersed phase, together with higher disordering of this phase, were observed in the ceramics obtained from MWCNT-containing precursor. The presence of MWCNT resulted in a ceramic matrix with a different morphology, in relation to that observed in the absence of MWCNT, with lower resistance to oxidation. Moreover, the extra C-source present in the ceramic matrix, introduced as MWCNT, reduced the solubility of SiO2 in this matrix, promoting the early segregation of SiO4-rich sites. Consequently, a more effective crystallization of SiO2, with relatively large c-SiO2 crystals, and of β-SiC occurred in the material with the increase of the heat treatment time.