THERMODYNAMIC AND EXPERIMENTAL-STUDY OF THE CHEMICAL-VAPOR CODEPOSITION IN THE SILICON-BORON-CARBON SYSTEM AT 1400-K

The results of a thermodynamic and experimental study of the codeposit ion of three elements, silicon, boron, and carbon, by a classical chem ical vapor deposition technique in a hot-wall reactor are compared. Th e initial gaseous mixture consisted of methyltrichlorosilane, boron tr ichloride, and hydrogen. By the thermodynamic approach, the nonstoichi ometry of boron carbide was described from B4C to B10C, and a comparis on can be made between accurate thermodynamic calculations and experim ental compositions measured at a given position on the substrate. The thickness and composition uniformity was also studied as a function of the inlet gas composition. The codeposits were first obtained on grap hite, but the final purpose was to extend the process to composite mat erials. When fixed conditions of temperature (T = 1400 K) and total pr essure (P = 0.395 atm) were employed, the influence of the total gaseo us flux was shown to be great, especially in a hot-wall reactor. The t otal flux can change the deposition results because of either the depl etion phenomenon or some departure from equilibrium.