Preparation of hollow SiC ceramic fibre from polycarbosilane fibre by diffusion-controlled cross-linking method

Cross-linking is favourable for increasing ceramic yield and avoiding melting or deformation of SiC ceramic precursor polycarbosilane (PCS) during pyrolysis. In order to achieve hollow SiC fibre, PCS fibre with a limited cross-linking depth was prepared by chlorinating the Si–H group in the outer layer of PCS fibre followed by hydrolysis and condensation of the formed Si–Cl group. The chlorination was implemented through a gas–solid reaction between Cl2 and PCS fibre. Based on the results of energy-dispersive spectrometer and attenuated total reflectance–Fourier transform infrared spectroscopy, the diffusion-controlled chlorination reaction was confirmed. During hydrolysis, the catalysis of ammonia gas was necessary. According to the results of dissolution and degradation experiments, cross-linked PCS outer layer formed after chlorination, hydrolysis and condensation, and the outer layer had higher ceramic yield than the core part. After pyrolysis, SiC fibre with hollow morphology was formed. By adjusting the chlorination degree, the morphology of resulting hollow SiC fibre could be modified.