Fabrication of silicon oxycarbide fibers from alkoxide solutions along the sol-gel process

Spinnable solutions are obtained in the sol-gel system of tetraethoxide (TEOS, Si(OC2H5)(4)) and vinyltrimethoxysilane (VTMS, CH2=CHSi(OCH3)(3)) under aqueous condition (water) with acid catalysts (HNO3 and HCl). Polysiloxane (PSO) fibers are drawn from the solution and characterized by spectroscopic and structural analyses. Si-29-nuclear magnetic resonance NMR) spectral analysis of the PSO fiber indicates the incorporation of atomic carbon in the silica network. C-13-NMR analysis shows the existence of considerable amount of hydroxyl groups in the PSO fiber. The spinnablity of the solution is studied by varying the mole ratios of the alkoxides, solvents and catalysts as well as precursor chemistries. The amount of water and catalysts are found to be important for the attaining of a spinnable state in the solution. SiOC fibers are obtained after pyrolysis of the PSO fibers with a high ceramic yield (88 wt%). The high ceramic yield attributes to the incorporation of vinyl-groups in the gel fiber that enhances crosslinking during pyrolysis. The SiOC fiber has a tensile strength of 776 MPa and electrical conductivity of 3.6 x 10(-4) S/m.