Corrosion of Graphite-Fiber-Reinforced Composites II—Anodic Polarization Damage

In order to safely use graphite-fiber-reinforced polymer-matrix composites in structural applications, the long-term resistance of these materials to environmental degradation must be characterized. High-conductivity electrolytes such as seawater represent a commonly encountered and relatively benign environment. An electrolyte is unlikely to chemically attack polymer-matrix composites such as graphite/epoxy, and long-term exposure typically would result in only minor moisture-induced damage. However, the relatively high conductivity of graphite fibers coupled with a high-conductivity electrolyte may promote damaging electrochemical reactions to occur. Anodic polarization of graphite/epoxy (which could result from stray electrical currents) causes rapid and substantial corrosion damage at applied current densities as low as 1 μA/cm². Unlike metals, where corrosion damage results from direct electrochemical dissolution, damage of graphite-fiber polymer-matrix composites is the result of secondary chemical reactions involving electrochemically evolved species. Experimental evidence suggests that this damage is associated with oxygen evolution at the anode. The mechanism is thought to be attack by adsorbed atomic oxygen, which occurs as an intermediate in the O₂ evolution reaction.