A novel polyborosilazane for high-temperature amorphous Si–B–N–C ceramic fibres

Abstract

Polyborosilazane synthesised from BCl3, HMeSiCl2, and Me3SiNHSiMe3 is easy to cross-link for dehydrogenation of Si–H and N–H, which limits its practical applications for Si–B–N–C fibres on an industrial scale. Therefore, in this context, MeSiCl3 was used instead of HMeSiCl2 to synthesise a novel polyborosilazane with limited cross-linking density to fabricate Si–B–N–C fibres. The polyborosilazane synthesised from BCl3, MeSiCl3, and Me3SiNHSiMe3 exhibits good melt-processability and 1km long polyborosilazane fibre can be obtained by melt spinning. Prior to pyrolysis, chemical curing with vapour HSiCl3 at 80°C was utilised to make the λ green fibres infusible. The as-cured fibres were subsequently pyrolyzed at 1200°C in nitrogen atmospheres to provide Si–B–N–C ceramic fibres with ca. 1.5GPa in tensile strength, ca. 160GPa in Young's modulus, ca. 12μm in diameter and keeping amorphous up to 1700°C, which makes them to be promising reinforcements in ceramic matrix composites for high temperature applications.