Silicon Carbide Coating for Carbon Materials Produced by a Pack-Cementation Process

Abstract
A pack-cementation process has been developed in order to produce SiC coating on carbon materials. At high temperature gaseous silicon monoxide generated from a SiC-SiO₂ powders mixture reacts with carbon substrate by converting the outer surfaces into silicon carbide. The correlation between density measurements and thermochemical calculations allows to determine the reaction path mechanism for the SiC layer formation. Iridium marker experiments are proposed to localize the substrate initial surface position after cementation. It is thus established that the growth originates at the substrate-film interface. Using an original approach, it is pointed out that the growth results from a gaseous mechanism which carries the reaction silicon species through the SiC layer to the substrate. X-ray diffraction, transmission electron microscopy and density measurement permit some description of the cemented layer structure : the cementation leads to a fine porous coating of [MATH]-SiC. Polytypic stacking faults probably exist whose frequency qualitatively increases from the outer to the inner surface of the film.