Understanding thermodynamic stability and carbothermal reduction in SiOC

Abstract

This study explores the phase evolution, carbothermal reduction, and energetics in SiOaCb derived from the pyrolysis of trimethylsilyl terminated polyhydromethylsiloxane (PHMS-TMS) from 1200 to 1600 °C. High-resolution X-ray photoelectron spectroscopy (XPS) shows notable differences in the constituent bond arrangement between the more Si-rich SiOC ceramics and the more C-rich SiOC ceramics, which subsequently affects the microstructure of the SiOC systems. Carbothermal reduction starts at lower temperatures than previously reported and indicates no phase separation of SiOC or formation of SiO2 nanodomains. The thermodynamic stability of the thus-obtained SiOC ceramics is evaluated using a Gibbs free energy minimization method. The results suggest that differences in silicon mixed bonding environments and their relative amounts (SiO2C2, SiOC3, or SiC4) lead to differences in thermodynamic stability.