SiOC ceramic with high excess free carbon

The correlation between microstructure evolution and increasing processing temperature of a polymer-derived SiOC ceramic with a high volume fraction of free carbon was studied by transmission electron microscopy (TEM). The high carbon content of the SiOC ceramic was achieved by crosslinking the starting precursor polyhydridomethylsiloxane (PHMS) with divinylbenzene (DVB). Focus of the TEM characterization was the evolution of the carbon phase upon pyrolysis at 1000 °C and after additional heat treatment at 1450 °C. Although a continuous structural rearrangement within the bulk SiOC matrix was observed with raising temperature, the sample annealed at 1450 °C remained predominantly amorphous, with the exception of a percolation network of turbostratic carbon and a slight precipitation of nanosized SiC particles. The micro/nanostructure observed in this sample upon thermal treatment at high-temperature suggests a phase separation in small SiO4- and SiC4-rich regions encapsulated by carbon. This specific phase distribution is consistent with the exceptional thermo-mechanical properties reported for similar high C-content SiOC materials.