Structure and porosity of silicon oxycarbide/carbon black composites

This study describes the influence of carbon black (C-black) on structural evolution and porosity of silicon oxycarbide (SiOC)-based ceramics obtained from pyrolysis of silicone-derived polymeric precursors. Initially, polymeric precursors were synthesized by hydrosilylation reaction between poly(methylhydrosiloxane) (PHMS) and 2,4,6,8-tetramethyl-2,4,6,8-tetravinylcyclotetrasiloxane (D(4)Vi), with different C-black contents (0, 1, 3, 5 and 10 wt%), followed by pyrolysis under argon at 1000 and 1500 degrees C, to give rise to the respective SiOC/C-black ceramic composites. FTIR-ATR, TG, XRD, N-2 gas physisorption at 77 K were used to characterize the carbonaceous phase, preceramic polymers and resulting ceramics. C-black incorporation, together with the pyrolysis temperature, generated more porous ceramic materials and intensified the semiconducting SiC phase formation, maintaining the presence of conducting C-graphitic structures embedded into SiOC matrices. Results concerning structural and textural features were associated to the different distributions of C-black into polymeric precursors. Moreover, the availability of residual carbon to react with degradation products during pyrolysis and produce SiC and C-graphitic crystalline phases was reported. C-black immobilization into preceramic Si-containing polymers plays an important role to produce SiOC/C-black ceramic composites with predominance of electroactive phases. The presence of C-black also contributed to higher porosities on resulting composites, which are suitable features for electrochemical investigations in polymer-derived ceramic matrices.