Carbon: Science and Technology (Dec 2018)
Synthesis of ultra-high temperature silicon oxycarbide (SiOC) glass by an organic-inorganic hybrid route
Abstract
Silicon oxycarbide is a new generation amorphous glassy ceramic possessing unique electrical, mechanical, optical properties and ultra-high temperature stability upto 2730°C. It has numerous engineering applications in additive manufacturing, lithium-ion batteries, brake disks for sports car, ultra-fast and high voltage LEDs, MOSFETs, thyristors for high power switching, astronomical telescope, nuclear power reactor etc. In this work, SiOC was prepared by sol-gel technique using organic-inorganic hybrids as precursors. Tetraethoxysilane (TEOS) and Polydimethylsiloxane (PDMS) were used as silica and carbon sources respectively. SiOC sols were formed through hydrolysis of TEOS and PDMS. The used chemicals in this process involved isopropanol, distilled water and hydrochloric acid, which is used here as solvent, hydrolytic agent and catalyst respectively, at different refluxing condition, alkoxide to water ratios, pH levels etc. The sols thus formed were allowed to gel over a varying period (up to maximum of 10 days). After drying the gels for 24 hours, the same was pyrolysed at 1100°C under inert nitrogen atmosphere to yield SiOC. Phase formation was carried out by X-Ray Diffraction (XRD) technique, X-ray Photoelectron Spectroscopy (XPS) analysis and Raman Spectroscopic analysis. XRD data showed formation of a broad peak at 2θ~22 degrees indicating formation of amorphous SiOC and absence of any crystalline peaks indicating no SiC or Si was formed during pyrolysis. XPS data shows the presence of Si, O and C peaks in the range 100-200 eV, 530 eV and 285 eV, respectively, confirming formation of SiOC. It was revealed that within the random network of Si-O tetrahedra, islands of only C-C bonds were responsible for coloring the SiOC glass black. The estimation of mechanical properties revealed that the hardness value and Young’s modulus, of the synthesized SiOC ceramic sample, was determined to be 11.67 GPa and 75.79 respectively which indicating the better mechanical properties than other reported SiOC systems.
