THE DEPOSITION OF SILICA ON CARBON AS A MODEL SYSTEM FOR OXIDATION PROTECTION COATINGS

The nucleation and growth of silica deposited by CVD on various carbon substrates was studied with the goal of enhancing the effectiveness of oxidation protection coatings for carbon-carbon composites. In this study, the surfaces of graphitized carbon blacks and carbon fibers were characterized with scanning probe microscopy, chemical and physical adsorption, and flow microcalorimetry techniques. The data from all these techniques were correlated with silica deposition rate data on the various carbon surfaces to produce a model for the nucleation and deposition of silica on carbon fibers. Deposition occurs preferentially on the carbon active sites, and the surface is covered through a spillover process.