Production of B 4 C coatings by CVD method in a dual impinging‐jet reactor: Chemical yield, morphology, and hardness analysis

β‐rhombohedral boron carbide (B 4 C) was deposited on a tungsten substrate from a BCl 3 H 2 CH 4 gas mixture in a dual impinging‐jet chemical vapor deposition reactor. On‐line FTIR analysis of the product stream proved the formation of BHCl 2 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 B 4 C phase at 1300°C without any other B 4 C 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/mm 2 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