Crosslinking kinetics of polycarbosilane precursor in ozone atmosphere and the formation mechanism of continuous hollow SiC fiber

Crosslinking is favorable for increasing the ceramic yield of polycarbosilane precursor (PCS), so PCS fiber with crosslinked skin-uncrosslinked core structure may contribute to formation of hollow SiC fiber. In this study, diffusion-controlled ozone oxidation crosslinking method was adopted. EDS verified the oxygen element contributing to crosslinking mainly distributed in the outer layer of ozone-crosslinked PCS fiber (O - PCSf). After pyrolysis, SEM confirmed the formation of continuous hollow fiber and XRD indicated the presence of beta-SiC structure. N-2 adsorption-desorption measurement demonstrated that a lot of micropores and mesopores, which were the main escape paths for degradation product of uncrosslinked core part of O - PCSf and contributed to the formation of continuous hollow SiC fiber, formed along fiber during pyrolysis and disappeared after the pyrolysis temperature was increased. In addition, by adjusting ozone oxidation time and applying vacuum pyrolysis method, the morphology of resulting hollow SiC fiber could be further modified.