Fabrication and characterization of boron nitride bulk foam from borazine

•The BN foams exhibit controlled bulk densities varying from 0.08 to 0.25 g cm−3.•The specific compressive strength of BN foams vary from 35 to 55.•The low dielectric constant and low loss tangent with little variation.•The as-obtained BN foams provide excellent thermal insulation.•The BN foams are useful for high-temperature radomes and thermal insulation.

Boron nitride (BN) ceramic bulk foams larger than 10 × 10 × 1 cm are fabricated by the pyrolysis of polyborazine foams that are prepared by fast curing of borazine. The principle of the self-foaming phenomenon is the emitting of H2 in condensation polymerization during the curing of borazine. The as-fabricated BN ceramic foams exhibit closed cells with sizes ranging from 50 to 100 μm and controlled bulk densities varying from 0.08 to 0.25 g cm−3 depending on the different cured pressures. Studies on the microstructure and properties of the porous material show that the BN ceramic foams exhibit high specific strength, low dielectric constants and loss tangents, and good thermal conductivity. These characteristics make them useful for high temperature radomes and thermal insulation.