Electrochemical Impedance Spectroscopy Evaluation of Primed BMI- Graphite/Aluminum Galvanic System.

摘要

Use of bismaleimide (BMI)-graphite composite materials is on the rise in engineering applications, especially in the design of new state-of-the-art DoD and U.S. Navy aircraft. The primary advantage of BMI-based systems is the increase in service temperature range over conventional epoxies from approximately 300-350 to 400-450 deg F. During manufacture of aircraft components, as well as repairs to items damages in-service, BMI-graphite and aluminum parts need to be assembled together using either adhesives or fasteners. Under appropriate moisture conditions, a galvanic cell is established within the BMI-graphite/aluminum assembly that could result in degradation of the BMI resin. Real time recognition of this degradation during its early stages is essential in establishing a successful plan to correct the problem. Earlier Navy work performed in 2000 demonstrated that Electrochemical Impedance Spectroscopy (EIS) is a viable analytical technique that can be used for detection of BMI degradation at the molecular level prior to any visual evidence of the failing critical component made of the composite material. The work presented here provides EIS results on the performance of several configurations of titanium-bolted, primed EMI-graphite/aluminum assemblies exposed to 3.5% salt water at 180 deg F. Epoxy primer, following military specification MIL-P-23377, was applied to all surfaces prior to testing.