Large-scale preparation of SiBN ceramic fibres from a single source precursor

Large-scale production of SiBN ceramic fibres was achieved by the pyrolysis of N-methylpolyborosilazane. This precursor was prepared by a three-step synthesis starting from hexamethyldisilazane (HMDS), silicon tetrachloride (STC), boron trichloride (BTC), and methylamine. To prove the feasibility of the synthesis on both the large and laboratory scales, the structure and composition of the as-synthesised polymer was characterised by Fourier transform infrared (FT-IR) and Nuclear Magnetic Resonance (NMR) spectroscopy and elemental analysis (EA). Differential scanning calorimetry (DSC) showed that the obtained large-scale polymer had a wide glass transition temperature range (32 °C to 50 °C) and a low transition temperature (40.41 °C), making it suitable for melt spinning. Both the large- and lab-scale synthesised polymers were successfully processed into polymer green fibres by a melt spinning process under an inert atmosphere, as the synthesised polymer is air and moisture sensitive. Endless and crack-free green fibres above 1000 m in length were successfully collected on a rotating spool, followed by cross-linking and thermolysis up to 1000 °C in an ammonia atmosphere. The SiBN ceramic fibres are amorphous up to 1600 °C in a nitrogen atmosphere. The presented results emphasise a feasible approach to highly thermally stable SiBN ceramic fibres on a large scale starting from a greatly flexible single-source precursor.