A review of the catalytic oxidation of carbon-carbon composite aircraft brakes

This document is the Accepted Manuscript version, made available under the terms of the Creative Commons Attribution-NonCommercial-NoDerivatives License CC BY NC-ND 4.0 (http://creativecommons.org/licenses/by-nc-nd/4.0/. The final, definitive version of this paper is available online at doi: https://doi.org/10.1016/j.carbon.2015.08.100.The use of de-icing chemicals at airport runways has been shown to produce oxides and carbonates of sodium, potassium and calcium which catalyse the oxidation of carbon-carbon composite aircraft brakes leading to an increase of the oxidation rate by an order of magnitude. This review reports on studies that have characterised the catalytic oxidation and discusses the mechanism of the catalytic reaction based on investigations that were carried out with both C-C composites and carbon as a fossil fuel. The alkali metal oxides/carbonates are more active catalysts and in their case, the redox reaction between the monoxides and the peroxides has been identified as the most likely catalysis mechanism. In order to reduce or eliminate the problem of catalysis, doping with boron or phosphorus compounds has been investigated by a number of researchers. The effect of these along with the use of protective coatings is also reviewed.Peer reviewe

Oxidation Kinetics and Its Impact on the Strength of Carbon Short Fiber Reinforced C/SiC Ceramics

Because of the excellent fracture toughness and oxidation resistance, carbon short fiber reinforced ceramics have a sound potential for a variety of high-temperature applications. For the composite's reliable use in long-term applications, however, the oxidation effects on the mechanical strength are of crucial interest and have hitherto not been investigated in detail yet. In this study, the weight change of carbon short fiber reinforced C/SiC composites with carbon fiber lengths of 9 mm (long cut fiber composite – LCFC) and 2 mm (short milled fiber composite – SMFC), respectively, are evaluated in the temperature range from 500 to 1200 °C for two different fiber orientations. Both types of composites were additionally tested in bending mode after 25 and 50 min of exposure to air at 700 °C depending on fiber orientation. After 3 h of exposure at 1000 °C, a total weight loss of up to 37% for LCFC and 47% for SMFC could be determined. The bending test carried out after 50 min exposure at 700 °C showed a dramatic decrease down to 50% of the initial flexural strength for LCFC samples with fibers orientated in parallel to the beam axis. The smallest strength decrease of around 13% was found for SMFC samples with fibers orientated perpendicularly to the beam axis. Microstructural investigations suggest strongly that oxidation along the fibers is the most dominating weakening mechanism and is therefore directly affected by the fiber orientation and length