(267e) Bi-Functional Coating for Carbon-Carbon Composite Oxidation Protection
Carbon-Carbon (C-C) composites have several high temperature applications and have found particular relevance in the aerospace industry, especially in use as airplane brake disks. The high temperatures to which the C-C composites can be subjected during aircraft landing cause oxidation of the C-C composites, requiring the use of strong anti-oxidation preventative measures for any composite used at elevated temperatures. A novel anti-oxidation technique termed Functionally Graded Coatings (FGC) for cost-effective production of multi layer oxidation resistant coatings on the surface of the C-C composites has been developed and investigated. The FGC involves several protective layers (e.g., carbides, oxides, metal phosphates) produced in one step that have different anti-oxidation mechanisms, providing extremely high stability for high-temperature applications of C-C composites in oxidation environments.
The focus of this research was to determine if it was possible to retain phosphorous phase in a C-C composite after a high temperature electrically induced liquid infiltration (EILI) reaction and to determine if this approach would improve the coating's oxidation protection ability. The FGC is synthesized by high temperature rapid heterogeneous combustion reactions. In this study phosphorus acid was applied as active-site poisoning agents to inhibit oxidations by forming stable glassy complex barriers that will decrease oxygen diffusion, followed by a layer of silicon carbide (SiC) coating as a physical protection barrier on the surface of C-C composites via EILI. Preliminary thermal oxidation tests reveal that the average percent weight loss for C-C composite is decreased from 30.36 ± 3.76% to 18.88 ± 4.04%. Further catalytic oxidation tests indicated that it is reduced from 68.57 ± 3.46% to 23.04 ± 8.08%. Energy dispersive X-ray spectroscopy (EDX) analysis proved quantitatively that a portion of the phosphorous (~3 wt%) that was introduced into the C-C matrices remained in the composites even after the high temperatures reached during the reactions (1700°C). It was shown that phosphorous impregnation, although minimal, improved the oxidation prevention capabilities of the multi-layer coatings, when compared to systems containing no phosphorous.