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

Silicon carbide coatings of carbon substrates have been synthesized by reac tive pack cementation. The cement was a SiCSiO2 powder mixture, and the tem perature investigated ranged from 1400 to 1700 degrees C under an atmospher ic pressure of argon (104 kPa). From both thermogravimetric analyses (TGAs) and density measurements of the coated parts, an overall growth reaction h as 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 occ urrence of gaseous diffusion of the Si precursor through the coating has be en 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 c alculation of an apparent activation energy (E-a) that indicates that the c arbon/gaseous pha:je chemistry is the limiting step for short-time experime nts. For a longer duration and/or thicker coating, a gaseous diffusion-limi ting step occurs gradually. X-ray diffraction (XRD) and electron microscopy are used to characterize the SiC deposit.