Fundamental understanding of water vapor effect on SiOC evolution during pyrolysis

In this study, fundamental difference of polysiloxane derived SiOC from pyrolysis conditions with and without water vapor presence is evaluated from composition and microstructure points of view. Based on the composition analysis, it can be derived that the presence of water vapor preferentially removes the free carbon in the SiOC matrix. Because of the less dominant presence of carbon, SiC formation is suppressed; some SiO2 is reduced to Si. After the pyrolysis, SiO2 nanodomains can be removed and pores form with the HF etching to form highly porous microstructures. The graphitic layers form a connecting network encapsulating other phases present: SiO2, Si, and SiC; SiOC co-exists with the graphitic network. Without the constraint of the SiOC matrix and other crystalline phases, the graphitic layers can exfoliate and form disorganized single layers. (C) 2015 Elsevier Ltd. All rights reserved.