ANODIC POLARIZATION BEHAVIOR AND SURFACE- FILMS OF CVD-SIC IN AQUEOUS-SOLUTIONS

The anodic polarization behavior of SiC prepared by CVD has been exami ned in 1 kmol.m(-3) H2SO4(pHO), phosphate buffer solution (pH6.86), bo ric-borate buffer solution(pH8.45) and 0.1 kmol.m(-3) NaOH(pH12.8). Gr owth and composition of the surface film formed by the anodic polariza tion have been measured by ellipsometry, XPS, and IR spectroscopy. Max imum dissolution current densities under the anodic polarization were less than 1 A.m(-2) in the solutions. This shows the corrosion rate of SiC is quite small in the solutions. The corrosion rate of SiC increa sed with increasing the pH value oi solutions. The anodic oxidation fi lms which was estimated to be a hydrated amorphous SiO2 by XPS and IR spectroscopy were formed on SiC in the acid and neutral solutions, whe reas no film growth was found in the alkaline solution. The potential at which the formation of anodic oxidation film starts became lower wi th increasing pH. The conversion of composition of the SiC matrix occu rred under the anodic oxidation film when SiC was polarized to higher potentials. This converted matrix layer was composed of carbon-rich Si C and its refractive index was lower than that of the original SiC mat rix.