Mechanism studies on CVD of boron carbide from a gas mixture of BCL sigma ub 3 less than or equal to CH sigma ub 4 less than or equal to and H sigma ub 2in a dual impinging-jet reactor

Nearly pure boron carbide free from impurities was produced on a tungsten substrate in a dual impinging-jet chemical vapor deposition reactor from a BCl..., CH..., and H... mixture. The Fourier Transform Infrared (FTIR) analysis proved the formation of reaction intermediate BHCl..., which is proposed to occur mainly in the gaseous boundary layer next to the substrate surface. Among a large number of reaction mechanisms proposed only the ones considering the molecular adsorption of boron carbide on the substrate surface gave reasonable fits. In the proposed mechanism dichloroborane is formed in the gas phase only as a by-product. Boron carbide, on the other hand, is formed through a series of surface reactions involving adsorbed boron trichloride, adsorbed methane and gas phase hydrogen. The simultaneous fit of the experimental rate data to the model expressions gave correlation coefficient values of 0.977 and 0.948, in predicting the B...C and BHCl... formation rates, respectively. (ProQuest: ... denotes formulae/symbols omitted.)