Kinetics of conversion of silicon carbide to carbide derived carbon

Carbide derived carbon (CDC) was produced on SiC by reaction with flowing Ar-3.5% Cl-2 gas at 900 and 1000. C. The thickness of the CDC layer increased with time during high temperature exposure according to a parabolic rate equation represented by K-p = [2.48 x 10(-6)e(-)(165000/RT)]m(2)s(-1). Carbon loss due to the formation and spallation of graphitic powder was found to be negligible in these experiments. Residual chlorine contents in the CDC layer were measured, and a gradient in chlorine content increasing from the CDC/SiC interface to the CDC/gas interface was observed. This is consistent with diffusional transport of chlorine through the growing CDC layer as the rate controlling step in the CDC growth process. Because the value of the parabolic rate constant is high compared with solid state diffusion coefficients for carbon, transport by solid state diffusion is unlikely. Because the apparent activation energy of 165 000 J mol(-1) is high for a gas phase diffusion process, surface diffusion of adsorbed chlorine in the pores of the CDC is suggested as a transport mechanism for the growth of CDC under these conditions.