Fabrication of SiC fibers by combining dry spinning with thermal crosslinking

Crosslinking is a crucial step to keep fibrous morphology and improve ceramic yield in the fabrication process of SiC fibers. Comparing with the oxygen crosslinking, thermal crosslinking can reduce the introduction of oxygen within fibers. In this study, a novel method for preparing the SiC fibers was proposed by combining dry spinning and thermal crosslinking. The spinning solution was prepared by blending a low-molecular-weight (~ 1000 Da) polycarbosilane (PCS) with polyisobutene (PIB) as spinning additive, acrylic acid (AA) as crosslinking agent, and 2,2'-Azobis (2,4-dimethyl) valeronitrile (ABVN) as initiator. The crosslinking mechanism, morphology, composition and microstructure, and mechanical properties of fibers were investigated. The results showed that the morphology of AA-containing PCS fibers was well preserved at 300 ℃ with a low heating rate (0.5 ℃/min), while PCS fibers without AA exhibited the melting or deformation. The crosslinking reaction between C = C groups in AA-containing PCS and Si–H bonds in PCS was triggered by ABVN. Furthermore, AA-containing PCS green fibers experienced pyrolysis at 1100 ℃ and then were annealed at 1500 ℃ (denoted as SiC-1500). SiC-1500 fibers, with an average diameter of 10.47 ± 0.50 μm and average tensile strength of 1.35 ± 0.65 GPa, have a smooth surface and relative dense structure. But SiC-1500 fibers were still an amorphous structure due to the suppression of graphite phase for the growth of β-SiC grains. This work not only breaks through the limitations that only uses high-molecular-weight PCS for dry spinning, but also successfully combines dry spinning and thermal crosslinking technology to obtain SiC fibers.