Suppression of free Si formation during liquid phase sintering of polysiloxane-derived, porous silicon carbide ceramics

摘要

Porous silicon carbide ceramics were prepared from a polysiloxane, carbon black, SiC filler, sacrificial templates (co-polymer microbeads) and Al₂O₃-Y₂O₃ additives by a carbothermal reduction and subsequent sintering process. The effect of the sintering temperature on the microstructural development and structural characteristics of the porous ceramics was examined by scanning electron microscopy (SEM), X-ray diffractometry (XRD), and Raman spectroscopy. The polysiloxane-derived silicon carbide (PDSC) specimens showed a more homogeneous pore distribution than the powder-processed ones. Both the PDSC and powder-processed specimens contained only β-SiC when sintered at 1700°C. On the other hand, the PDSC specimens sintered at 2000°C revealed the formation of free Si clusters, detected by XRD and Raman spectroscopy, whereas the powder-processed ones showed only the SiC phases. The formation of such Si clusters was effectively suppressed by adding an excess of carbon during the synthetic process. Raman spectroscopy revealed the existence of carbon layers in the 1700°C-sintered specimens, which were hardly detectable in the 2000°C-sintered ones.