Borazine derived porous boron nitride–boron nitride composites fabricated by precursor infiltration and pyrolysis

Porous BN–BN composites were fabricated by unidirectional die pressing and precursor infiltration and pyrolysis (PIP) applying borazine as the precursor. The composition, mechanical, microstructural and dielectric properties of the composites were investigated. Pure hexagonal BN–BN composites with different properties can be obtained at temperatures between 1200 °C and 1600 °C. With increasing the pyrolysis temperature, the open porosity of the composites decreases whilst their bulk density and mechanical properties increase. When pyrolyzed at 1600 °C, the density, the flexural strength, elastic modulus and fracture toughness of the composites are 1.81 g cm−3, 39.78 MPa, 31.84 GPa and 1.46 MPa m1/2 respectively. Meanwhile, the dielectric constant (ε) and loss tangent (tan δ) of the composites are 2.7 and 0.0052. The microstructural transition from piece bonding to piece stacking can be found as well.