Polyorganoborosilazane ((B[C₂H₄–Si(CH₃)NH]₃)_n) was synthesized via monomer route from a single-source precursor and thermolyzed at 1300 ℃ in argon atmosphere. The as-thermolyzed Si–B–C–N ceramic was characterized using X-ray diffraction (XRD) and Raman spectroscopy. The crystallization behavior of silicon carbide in the as-thermolyzed amorphous Si–B–C–N matrix was understood by XRD studies, and the crystallite size calculated using Scherrer equation was found to increase from 2 nm to 8 nm with increase in dwelling time. Concomitantly, Raman spectroscopy was used to characterize the free carbon present in the as-thermolyzed ceramic. The peak positions, intensities and full width at half maximum (FWHM) of D and G bands in the Raman spectra were used to study and understand the structural disorder of the free carbon. The G peak shift towards 1600 cm^-1 indicated the decrease in cluster size of the free carbon. The cluster diameter of the free carbon calculated using TK (Tuinstra and Koenl) equation was found to decrease from 6.2 nm to 5.4 nm with increase in dwelling time, indicating increase in structural disorder.

This work focused on the fabrication of silicon oxycarbide ceramic (SiOC) foams as well as dense compacts using poly(hydridomethylsiloxane) (PHMS) as a polymer precursor. The room-temperature cross-linking of PHMS was achieved by the addition of 1,4-diazabicyclo [2.2.2] octane (DABCO) with the release of hydrogen gas as a by-product. This resulted in self-blowing of the polymer precursor at room temperature and thereby offered the possibility of producing SiOC foams without the need of any external blowing agents. We also reported the fabrication of crack-free silicon oxycarbide compacts by cold compaction and pyrolysis route using polyvinyl alcohol (PVA) as a processing additive. Cylindrical-shaped pellets were pyrolysed at 1300 ℃ in argon atmosphere with a ceramic yield of approximately 85%. Increased resistance to phase separation and crystallization up to 1400 ℃ was attributed to the presence of large volume fraction of free carbon in the material which was confirmed by Raman spectroscopy.