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Relationship of Graphite-Polyimide Composites to Galvanic Processes

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Abstract

The possibility of galvanic action between graphite composites and metals has long been recognized. Recently, at General Dynamics Fort Worth Division, it was discovered that imide-linked resins can degrade under certain laboratory conditions involving the galvanic process. The galvanic coupling was found to cause hydroxyl ions to be formed at the gaphite cathode, hence attacking the O-C-N bond of the polyimide ring structure. Degradation was found ro initiate at exposed graphite sites at salt water/fuel or salt water/stagnant air interfaces. The phenomenon was found to occur in bismaleimides (BMI), condensation polyimides, triazines, and blends thereof. Standard galvanic protection schemes were demonstrated to be effective in preventing degradation, particularly when proper treatment of the composite was provided. Note: Since this was the first time polymer degradation (corrosion) by glavanic action was mentioned in the literature, that "plastics can corrode" these results have been referred to as "faudree effect" by workers in the aerospace industry.
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