Chemical vapor deposition of B13C2 from BCl3-CH4-H-2-argon mixtures

The deposition of boron carbide (B13C2) onto graphite substrates was accomp lished by using a hot-wall chemical vapor deposition (CVD) reactor at a pre ssure of 10.1 kPa in the temperature range of 1000 degrees-1400 degrees C. A modified inpinging-jet geometry was used to simplify the mass-transfer an alysis. Coatings were characterized using X-ray diffractometry (XRD), scann ing electron microscopy (SEM), and transmission electron microscopy (TEM). The surface morphology was composed of well-defined facets, the size of whi ch was dependent on the growth rate and deposition time, as would be expect ed from a competitive growth mechanism. TEM micrographs of the coating show ed long, columnar grains that emanated from a narrow nucleation zone. The g rowth rate could be adequately described by a first-order kinetic expressio n, 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.