In-situ techniques for studying deterioration of C/C composite aircraft brakes by catalytic oxidation

Recent use of potassium acetate as a runway deicer fluid at the airports leads to rapid wear of aircraft brakes. In this study, the deterioration of carbon/carbon composite aircraft brakes by oxidation was studied using samples of new and used brake materials. Insitu techniques, including Environmental Scanning Electron Microscopy (ESEM) and in-situ X-Ray Diffraction (ISXRD) were used together with thermal gravimetric analysis (TGA) to study the oxidation mechanisms and kinetics of oxidation. The new brake samples impregnated with potassium acetate showed high oxidation reactivity at relatively low temperatures, indicating catalysis of carbon oxidation by potassium species. Samples of used brake were more resistant to weight loss in air probably because the more reactive carbon components had already been gasified. ESEM experiments showed that particles of potassium oxides are very effective in catalysing the gasification of isotropic carbon fibers in the CVD composite. Potassium oxides identified by in situ XRD experiments seem to be present as molten phase, suggesting that an oxidation-reduction cycle with the intermediate formation of peroxide, or a higher oxide of potassium, is responsible for the observed catalytic effect.