OXIDATION OF THE CARBON INTERFACE IN NICALON-FIBER-REINFORCED SILICON-CARBIDE COMPOSITE

The recession rates for 10(-6)-m-thick C interfaces in chemical vapor infiltrated SIC reinforced with Nicalon fibers were calculated from th ermogravimetric data, assuming all of the mass losses were due to C ox idation, and found to be consistent with the measured recession distan ces of the C interface, which were surprisingly uniform across the com posite, Agreement between the two approaches for a microstructurally c omplex material indicates thermogravimetric analysis could be an impor tant tool for understanding environmental effects in ceramic composite s with reactive interfaces, Mass losses were linear within the first 1 .08 x 10(4) s to 2.16 x 10(4) s between 1073 and 1373 K and between 3. 1 x 10(2) and 2.5 x 10(3) Pa O-2. Calculated reaction orders with resp ect to O-2 were between 0.5 and 1.0 at 1373 K, and activation energies were about 50 kJ . mol(-1). Analysis of the kinetic data and estimate s of gas boundary layer thickness suggest the mechanism for the C-inte rface oxidation involved reaction control, but the possibility of diff usion control for some conditions cannot be ruled out.