Chemical vapor deposition of B₁₃C₂ from BCl₃-CH₄-H₂-argon mixtures

The deposition of boron carbide (B₁₃C₂) onto graphite substrates was accomplished by using a hot-wall chemical vapor deposition (CVD) reactor at a pressure of 10.1 kPa in the temperature range of 1000°-1400°C. A modified impinging-jet geometry was used to simplify the mass-transfer analysis. Coatings were characterized using X-ray diffractometry (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). The surface morphology was composed of well-defined facets, the size of which was dependent on the growth rate and deposition time, as would be expected from a competitive growth mechanism. TEM micrographs of the coating showed long, columnar grains that emanated from a narrow nucleation zone. The growth rate could be adequately described by a first-order kinetic expression, with respect to the bulk gas phase boron chloride (BCl₃) concentration. The activation energy of the kinetic expression was estimated to be 93.1 kJ/mol. It was proposed that the deposition was limited by the adsorption of (BCl₃) onto the substrate surface.