Carbothermal Synthesis of Boron Nitride Coatings on Silicon Carbide

Abstract

Pure BN coatings have been synthesized on the surface of SiC powders and fibers by a novel carbothermal nitridation method. Three stages are involved in the process: first, formation of a carbon layer on the SiC by the extraction of Si with chlorine; second, infiltration of the resulting nanoporous carbide‐derived carbon (CDC) coating by a saturated boric acid solution; and finally, nitridation in ammonia at atmospheric pressure to produce the pure BN coating. X‐ray diffraction (XRD), Raman spectroscopy, scanning electron microscopy (SEM), high‐resolution transmission electron microscopy (HRTEM), and electron energy loss spectroscopy (EELS) were used to characterize the phase, elemental composition, and surface morphology of the coatings. The intermediate carbon layer acts as a template for BN growth, facilitates the formation of BN, and prevents the degradation of SiC fibers during nitridation. The whole process is simple, cost‐effective, and less toxic due to the use of H3BO3 and NH3 as precursors at atmospheric pressure compared with most commonly used chemical vapor deposition (CVD) methods. Uniform BN coatings obtained by this method prevent the bridging of fibers in the tow. The coating of powders is possible, which cannot be achieved by conventional CVD methods.