Dielectric properties of BN modified carbon fibers by dip-coating

Continuous and uniform boron nitride (BN) coatings were synthesized on carbon fibers by dip-coating and their microstructure, chemical composition and dielectric properties were investigated. Results show that the as-prepared coatings are composed of phase mixture of h-BN and amorphous t-BN. The oxidation property of the BN modified carbon fibers is improved with higher initial and final oxidation temperatures. Both the real (ε′) and imaginary part (ε″) of permittivity of the BN modified carbon fibers decrease significantly compared with the pure carbon fibers. The decrease of ε′ can be mainly attributed to the absence of dielectric relaxation effect, while the decrease of ε″ can be ascribed to the large decrease in electrical conductivity. The decreasing permittivity leads to increase of microwave impedance which is beneficial for electromagnetic matching. With improved impedance match and still relatively high ε″, the BN modified carbon fibers exhibit a promising prospect as microwave absorbing materials.