N. Jacobson, R. Rauser, D. Roth, NASA Glenn Research Center, Cleveland, OH; N. Webster, Lockheed Martin, Ft. Worth, TX; D. Curry, NASA Johnson Space Center, Houston, TX
Reinforced Carbon/Carbon on the Space Shuttle Orbiter Wing Leading Edge and Nose Cap has a proven record of success over many missions. It is composed of a two dimensional lay-up of carbon fiber fabric with an oxidation protection system consisting of a conversion coating of SiC and glass sealants to plug pores and fissures. The major routes of degradation are sealant loss and sub-surface oxidation. Sealant loss is most likely caused by shear forces and vaporization. Sub-surface oxidation is caused by diffusion of oxygen through pores and fissures to the carbon/carbon substrate. A series of laboratory experiments have been conducted to understand these processes in depth and develop models. Sealant loss can be described by boundary layer limited diffusion of the vaporizing constituents. Sub-surface oxidation creates voids at the base of a pore or fissure in the SiC conversion coating. It is essential to distinguish these oxidation voids from voids formed during processing. Carefully prepared cross section and optical microscopy are particularly helpful in identifying oxidation damage. High resolution x-ray computed tomography (CT) scans are also helpful. Oxidation kinetics of RCC are reported and compared to a two-stage diffusion controlled model. From these and other studies, a basic understanding of RCC in the aggressive re-entry environment is emerging.
Summary: This paper will summarize research on degradation of reinforced carbon/carbon (RCC) at high temperatures.
