Silicon still exists in boron nitride(BN)ceramic fibers which were prepared by melt-spinning, curing with BCl₃ and pyrolysis under NH₃ of a preceramic silicon-containing polyborazine.That is because B-N(SiMe₃)₂ and B-N(SiMe₃)-B could not react with BCl₃ completely for the steric hindrance.So HCl was used to react with silicon-containing polyborazine first to reduce its steric hindrance.Then,BCl₃ reacted with silicon-containing polyborazine to remove the residual SiMe₃.After pyrolysis under NH₃,BN ceramic fibers without silicon were obtained which was proved by FT-IR and X-ray diffraction.The obtained BN ceramic fibers with diameter of about 11μm were dense which was demonstrated by scanning electron mi- croscopy(SEM)and the fibers showed room temperature mechanical property with average tensile strength of 0.45GPa.

Key words: BN ceramic fiber, polymer pyrolysis, silicon-containing polyborazine