Structure and porosity of silicon oxycarbide/carbon black composites

Abstract

This study describes the influence of carbon black (Cblack) 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 (D4Vi), with different Cblack contents (0, 1, 3, 5 and 10 wt%), followed by pyrolysis under argon at 1000 and 1500 °C, to give rise to the respective SiOC/Cblack ceramic composites. FTIR-ATR, TG, XRD, N2 gas physisorption at 77 K were used to characterize the carbonaceous phase, preceramic polymers and resulting ceramics. Cblack incorporation, together with the pyrolysis temperature, generated more porous ceramic materials and intensified the semiconducting SiC phase formation, maintaining the presence of conducting Cgraphitic structures embedded into SiOC matrices. Results concerning structural and textural features were associated to the different distributions of Cblack into polymeric precursors. Moreover, the availability of residual carbon to react with degradation products during pyrolysis and produce SiC and Cgraphitic crystalline phases was reported. Cblack immobilization into preceramic Si-containing polymers plays an important role to produce SiOC/Cblack ceramic composites with predominance of electroactive phases. The presence of Cblack also contributed to higher porosities on resulting composites, which are suitable features for electrochemical investigations in polymer-derived ceramic matrices.