Comparison of effects of nitrogen sources on the structures and properties of SiBNC ceramic fiber precursors

Polyborosilazane synthesized from trichlorosilane (SiHCl3), boron trichloride (BCl3) and methylamine (MeNH2) is highly sensitive to moisture for hydrolysis of -NHMe unites and is easy to cross-link for dehydrogenation of SiH, N-H, which affected the industrial scale production of SiBNC ceramic fibers. In this paper,a new nitrogen source(n-propylamine, C3H7NH2) was used instead of MeNH2 to synthesis polyborosilazane precursor. The influences of nitrogen sources on the structures and properties of SiBNC ceramic fiber precursors were investigated. As compared to SiHCl3/BCl3/CH3NH2 system, polyborosilazane precursor synthesized from the SiHCl3/BCl3/C3H7NH2 system exhibited lower crosslink density, lower sensitivity to moisture and good melt spinnability, and the obtained ceramic fibers showed higher tensile strength (1.03 GPa, an increase of about 37.3%). This synthesis route (SiHCl3/BCl3/C3H7NH2) may serve as a suitable synthetic route for a large-scale production of SiBNC ceramic fibers.