Hexagonal boron nitride from a borazine precursor for coating of SiBNC fibers using a continuous atmospheric pressure CVD process

The aim of this work is the coating of SiBNC fibers with hexagonal boron nitride (h-BN) for ceramic composite applications. h-BN is deposited from borazine in a vertical, hot-wall, atmospheric pressure (AP)CVD system. The effects of deposition parameters (e.g., temperatures, reactant concentrations, and gas velocity) on the deposition rates are investigated using Si(100) substrates statically placed at various positions in the reactor. The highest deposition rates are observed at 1090°C. It is found that ammonia is necessary for a satisfying coating deposition and for low oxygen incorporation, though high concentrations decreased the deposition rate. The coating structures are characterized using scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared (FTIR) spectroscopy. Based on the results of static h-BN deposition on Si substrates, h-BN is continuously and homogenously coated on SiBNC multifilaments with a fiber draw speed of 5m h -1. The thickness of the coating on SiBNC fibers is 180-200nm as measured by SEM. The h-BN coatings from our experiments have no influence on the mechanical strength of the SiBNC fibers.