A study of boron nitride coatings on carbon fibers by the powder immersion reaction method

Boron nitride (BN) coatings were successfully formed on the surface of carbon fibers by the powder immersion reaction method with boric acid and urea as precursor, followed by nitridation at 650 °C, 850 °C and 1050 °C in nitrogen, respectively. The composition, structure, morphology and phase of the samples were characterized in detail and the influence of different temperatures on the quality of BN coatings was systemically investigated. It was observed that the amorphous BN could be obtained at lower temperature, and with the increase of temperature, the amorphous BN gradually transformed into the hexagonal BN (h-BN) with high crystallinity. The coatings obtained on the surface of carbon fibers were continuous without cracking or peeling and combined closely with the substrate. The oxidation resistance of the coated carbon fibers was significantly higher than the uncoated carbon fibers. The coated carbon fibers maintained the tensile strength about 93% of its original strength.