Production of B₄C coatings by CVD method in a dual impinging-jet reactor: Chemical yield, morphology, and hardness analysis

β-rhombohedral boron carbide (B₄C) was deposited on a tungsten substrate from a BCl₃---H₂---CH₄ gas mixture in a dual impinging-jet chemical vapor deposition reactor. On-line FTIR analysis of the product stream proved the formation of BHCl₂ and HCl as by products, in a competing parallel reaction. A maximum of 13% chemical yield of boron carbide was observed, and the yield was found to have increasing trend with an increase in temperature. XRD analysis proved the existence of rhombohedral B₄C phase at 1300°C without any other B₄C phases or impurities. At this temperature, the formation of 5-fold icosahedral boron carbide crystals up to 30 micron sizes was observed. Such highly symmetric crystalline regions were observed to have a very high hardness value of 4750 kg/mm² as revealed from the microhardness analysis. The change in product morphology at low substrate temperatures resulted in a decrease in the hardness values. © 2009 American Institute of Chemical Engineers AIChE J, 2009