MASS-TRANSFER AND KINETICS OF THE CHEMICAL-VAPOR-DEPOSITION OF SIC ONTO FIBERS

An internally consistent set of data was generated for the chemical va por deposition (CVD) of SiC from methyltrichlorosilane (MTS) and H-2 a t atmospheric pressure. A moving fiber tow was used as the substrate. Coating rates between 0.3 and 3.7 mu m/min and deposition efficiencies between 24 and 48% were obtained for MTS and H-2 how rates in the ran ge 30 to 200 cm(3)/min and 300 to 2000 cm(3)/min, respectively. The da ta were analyzed and found to be best fit under a mass transfer regime . Based on this fit, a value of the constant in the Chilton-Colburn j factor expression for a moving fiber tow was estimated to be 2.74 x 10 (-6) with a standard deviation of 3.2 x 10(-7). The efficiency of the reaction was found to decrease with increases in the total flow rate, indicating that the effect of the decreased residence time of reagents in the reactor was larger than the increase in the mass transfer coef ficient. Finally, a comparison between the efficiencies for a stationa ry and a moving tow revealed that the moving tow had a higher efficien cy, possibly due to a disruption of the boundary layer by the tow moti on or due to the decrease in the canning of the moving tow.