Silicon carbide coating by reactive pack cementation - Part II: Silicon monoxide/carbon reaction

Silicon carbide coatings of carbon substrates have been synthesized by reactive pack cementation. The cement was a SiC-SiO2 powder mixture, and the temperature investigated ranged from 1400 to 1700 °C under an atmospheric pressure of argon (104 kPa). From both thermogravimetric analyses (TGAs) and density measurements of the coated parts, an overall growth reaction has been proposed. A multilayer experiment allowed us to establish that the growth is located at the SiC-C interface. Due to an original setup, the occurrence of gaseous diffusion of the Si precursor through the coating has been demonstrated. A volume increase in the cemented substrate has been shown, and its correlation with the substrate density is explained by means of a simple growth model. The overall reaction kinetics study has allowed the calculation of an apparent activation energy (Ea) that indicates that the carbon/gaseous phase chemistry is the limiting step for short-time experiments. For a longer duration and/or thicker coating, a gaseous diffusion-limiting step occurs gradually. X-ray diffraction (XRD) and electron microscopy are used to characterize the SiC deposit.