Continuous sol–gel derived SiOC/HfO2 fibers with high strength

Abstract

This study presents the fabrication and characterization of continuous SiOC/HfO₂ fibers with high strength by the sol–gel process. Continuous polyhafnosiloxane (PHfSO) gel fibers are spun from the solutions of silicon alkoxides and hafnium dichloride using polyvinyl pyrrolidone as a spinning reagent, and then transform into dense SiOC/HfO₂ fibers with homogeneous shrinkage by subsequent drying and pyrolysis treatment. Fourier transform infrared and X-ray photoelectron spectra together with X-ray diffraction analysis indicate that the amorphous SiOC/HfO₂ fibers consist of mixed silicon oxycarbide (SiO_xC_4−x, x = 1–4) and tetravalent hafnium–oxygen units embraced with a certain free-carbon phase. Scanning electron microscopy and transmission electron microscopy observations reveal that the SiOC/HfO₂ fibers with homogenous Hf distribution exhibit a circular-shaped or an elliptical-shaped cross-section depending on their thickness when employed as gel fibers. Mechanical testing shows that the SiOC/HfO₂ fibers exhibit good mechanical property with the maximum tensile strength of 1.5 GPa arising from the incorporation of Hf in the SiOC network.