Preparation and study on microwave absorbing materials of boron nitride coated pyrolytic carbon particles

Boron nitride coatings were synthesized on pyrolytic carbon (BN-coated PyC) particles via chemical reaction of boric acid and urea in nitrogen. The results of Scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FI-IR) and X-ray photoelectron spectroscopy (XPS) show the formation of boron nitride coating. The TGA curves indicate that the oxidation resistance of the PyC particles is improved by incorporating BN coating on the surface. The mass of the BN-coated PyC particles remains over 60% at 1200 °C whereas the PyC particles are oxidized completely at 920 °C. The investigation of microwave absorbing property reveals that compared with the PyC particles, the BN-coated PyC particles have lower permittivity (ɛ′, ɛ″) and better absorbing property. The BN-coated PyC particles show a strong absorbing peak at 10.64 GHz, where the lowest reflectivity −21.72 dB is reached. And the reflectivity less than −10 dB is over the range of 9.6-12 GHz.