Curing green fibres infusible by electron beam irradiation for the preparation of SiBNC ceramic fibres

Curing green fibres infusible is an essential procedure for the preparation of SiBNC ceramic fibres. Previously, green fibres had been fabricated by one-pot synthesis of polyborosilazane (PBSZ) and melt-spinning. In this paper, we attempted to use the method of electron beam irradiation to crosslink green fibres. The variation of molecular structures from green fibres to cured fibres and the properties of sintered SiBNC fibres were investigated. Via electron beam irradiation, the free radicals are formed at the C atoms and Si atoms on the -N-SiH(CH3)- main chain units and terminal -Si(CH3)3 groups. The radicals react with each other to produce cross-linking, coupling and grafting among PBSZ chains, which all contribute to improvement of the cross-linking density of green fibres. The cured fibres performed a high ceramic yield of 80.4 wt%. After pyrolysis at 1500 °C, SiBNC ceramic fibres were acquired, which exhibited a good flexibility with 12 µm in diameter and 1.22 GPa in tensile strength. The obtained fibres could remain amorphous up to 1700 °C and showed no mass loss at this temperature.