Chemical vapor deposition and lattice constant measurements of boron carbide
Rhombohedral boron carbide was deposited onto graphite substrates by a reaction between BCl₃, CCl₄, and H₂ at temperatures from 1000°C- 1275°C. The substrates were heated by r.f. induction and by placement inside a modified Astro Industries resistance furnace. Experimental parameters were varied to test their effects on composition of deposits and crystallite size. Deposits were obtained with compositions ranging from ~9 at.%C to ~20 at.%C. The largest crystallites obtained were approximately .1 mm in length with compositions of ~20 at.%C. Lattice constant calculations were made from Debye-Scherrer data obtained from the deposited samples and from sintered samples supplied by G. A. Technologies and compared to results in the literature. Possible explanations were considered for the inconsistency in the available data concerning the dependence of the lattice constants on composition. There are three probable reasons for the inconsistency: 1) failure to allow solid state reactions to continue to completion, 2) pressure dependence of the crystal structure, and 3) inaccuracies in compositions obtained by chemical analysis. However, it was impossible to conclude from the available information whether any or all of these reasons are definitely responsible.