Oxidation of the Carbon Interface in Nicalon-Fiber-Reinforced Silicon Carbide Composite

• Published in: Journal of the American Ceramic Society 1997-03, Vol.80 (3), p.569-574
• Main Authors: Windisch, Charles F., Henager, Charles H., Springer, Gary D., Jones, Russell H.
• Format: Article
• Language: English
• Subjects: Applied sciences; Building materials. Ceramics. Glasses; Ceramic industries; Chemical industry and chemicals; Exact sciences and technology; Structural ceramics; Technical ceramics
• ISSN: 0002-7820; 1551-2916
• DOI: 10.1111/j.1151-2916.1997.tb02868.x

The recession rates for 10‐6‐m‐thick C interfaces in chemical vapor infiltrated SiC reinforced with Nicalon fibers were calculated from thermogravimetric data, assuming all of the mass losses were due to C oxidation, and found to be consistent with the measured recession distances of the C interface, which were surprisingly uniform across the composite. Agreement between the two approaches for a microstructurally complex material indicates thermogravimetric analysis could be an important tool for understanding environmental effects in ceramic composites with reactive interfaces. Mass losses were linear within the first 1.08× 104 s to 2.16× 104 s between 1073 and 1373 K and between 3.1× 102 and 2.5× 103 Pa O2. Calculated reaction orders with respect to O2 were between 0.5 and 1.0 at 1373 K, and activation energies were about 50 kJmol‐1. Analysis of the kinetic data and estimates of gas boundary layer thickness suggest the mechanism for the C‐interface oxidation involved reaction control, but the possibility of diffusion control for some conditions cannot be ruled out.