Synthesis of SiOC using solvent-modified polymer precursors

Silicon oxycarbide ceramics are an important class of materials that can be modified to cover a wide range of microstructures and compositions during processing. This study focuses on a polysiloxane precursor to SiOC conversion when crosslinked in the presence of 0, 50, 100, and 200 vol% of 3-pentanone, n-heptane, or isobutylbenzene, relative to the volume of the polysiloxane. The solvent modified samples show a decrease in bulk density and an increase in open porosity. The addition of the solvents facilitates the formation of crystalline SiC, especially for 3-pentanone. The ability of the solvents to encourage SiC formation is directly related to the solvent molecular size, with smaller solvents being more likely to increase polymer chain entanglement and remain trapped within the polymer after drying and subsequently creating more C-C and Si-C bonds after pyrolysis. This work shows the unique function of solvents in modifying the SiOC microstructures and properties.