Influence of pyrolysis conditions on fabrication of polymer-derived BN fiber for wave transparent application

Boron nitride (BN) fiber was fabricated by pyrolysis of a poly[(alkylamino)borazine]. The influence of pyrolysis temperature, atmosphere, holding time and heating rate on the polymer fiber’s ceramic yield and carbon content of as-obtained BN fiber was investigated. The structural evolution of the polymer fiber during pyrolysis was characterized. The result revealed that the ceramic yield decreased with increasing of temperature and NH3 concentration, whereas decreased with reduction of heating rate. Moreover, the carbon content decreased with increasing of temperature, holding time and NH3 concentration, but contrarily, increased with enhancement of heating rate. Near stoichiometric BN fiber was prepared by pyrolysis under NH3/N2 atmosphere and then in Ar. Further heat treatment in Ar promoted the crystallization of BN fiber. The BN fiber with low dielectric constant and loss tangent exhibited a tensile strength of 850 MPa, showing great promise as a novel structural–functional fiber in microwave-transparent composites.