Effects of firing process on the composition, structure, and properties of near stoichiometric SiC fiber

Two kinds of near-stoichiometric SiC fibers were prepared through the pyrolysis of oxygen-free cured polycarbosilane fibers at 1,000 °C within a controlled hydrogen atmosphere, followed by sintering at 1,500 °C under a nitrogen atmosphere by one-step and two-step firing processes. The compositions, structures, and properties of the obtained SiC fibers were characterized using elemental analysis, mechanical performance testing, X-ray diffraction analysis, X-ray photoelectron spectroscopy, scanning electron microscopy, and transmission electron microscopy. Silicon radicals were generated in the process of hydrogen firing, which readily reacted with oxygen to form SiO₂ or SiC_xO_y phases on the fiber surface, resulting in the obtained fibers exhibited a gradient in compositional distribution across the radial direction, with higher oxygen content at their surfaces and higher carbon content at their cores. The strength of one-step-fired SiC fiber exceeded 1 GPa after treatment at 1,800℃ in argon and 1,500℃ in air for 1 h.