Experimental study of the chemical deposition of boron carbide from mixtures of boron trichloride, methane and hydrogen

The influence of the experimental parameters temperature, inlet gas composition and mass flow rate on the chemical vapour deposition of boron carbide from BCl3-CH4-H2 mixtures is studied. From the deposition rates and the solid composition measurements it is shown that the interfacial conditions of deposition can be very different, even when solids of the same composition are deposited; different microstructures can then be obtained which are distinguished by their degree of crystallization. The sensitivity of the deposition rate and the solid composition to variations in the gas composition and the flow changes as a function of the principal limiting stage of the process; this stage is either the surface kinetics or the gaseous mass transfer. Conditions to obtain continuous and homogeneous coatings of large size are inferred. A non-destructive, rapid and experimentally simple technique of fast γ ray spectroscopy using a beam of α particles is employed to determine the solid composition. (Auth.)