Achieve EMI Shielding Without Galvanic Corrosion in the Defence and Aerospace Industries
Electromagnetic interference (EMI) shielding is a critical part of high-performing defence and aerospace electronic applications, and engineers must take care to select materials that are suitable for the intense environments and situations these applications operate in. One challenge that often presents itself is corrosion, which unfortunately all metals are susceptible to. Galvanic corrosion occurs when two different metals have physical or electrical contact with each other and are immersed in a common electrolyte.
There are three major causes of galvanic corrosion:
- Dissimilar metals – there is a difference in the electrical potentials of the two metals that are in contact with one another.
- Conductive path – there is an electrical path between the two metals.
- Presence of electrolytes – a fluid such as atmospheric humidity or salt fog exists that is able to break down the metals.
Galvanic corrosion is a costly headache for U.S. government defense and aerospace applications. According to Government Accountability Office, corrosion costs the Department of Defense more than $21 billion a year due to rework and increased maintenance needs with a majority of the corrosion caused by harsher Class C and Class D environments.
In addition to reducing the astronomical cost associated with corrosion, there are many reasons to make managing it a priority. Reducing or eliminating corrosion extends equipment field life in any environment, improves equipment field performance and reliability, and provides design flexibility for dual or single seals.
Strategies to protect against galvanic corrosion
How do you protect against galvanic corrosion? As much as removing a conductive path between the two dissimilar metals would be a great solution, you unfortunately can’t remove the conductive path and maintain an EMI seal at the same time. That’s because the nature of an EMI gasket is to create a conductive path.
One effective corrosion mitigation strategy is to create an environmental seal. If you can prevent the interface between metals from external elements, you can prevent the corrosion from occurring. You must protect the EMI gasket from humidity or moisture in the air. The addition of a non-conductive gasket is an example of a product that can create a moisture barrier, so you don’t have that corrosion-causing electrolyte (moisture) present in the system.
Another strategy is to use metals that have similar electrochemical potentials. Parker Chomerics does this by developing custom plated metal particles which minimise the electrochemical potential difference the conductive metal particles and the metal substrates to which they are applied.
EMI shielding solutions designed to minimise corrosion
At Parker Chomerics, they make EMI shielding solutions that are specifically designed to protect against corrosion. One area of focus for them is particle development where they either modify the electrically conductive particles or use specific materials that are meant to minimise corrosion. For example Parker has developed silver-plated aluminum and nickel-plated aluminum particles that provide great galvanic corrosion resistance on aluminum substrates.
Parker has extensively tested different materials to offer a proven catalog of products that are up to the challenge. Here are a few of their EMI shielding solutions that were designed with corrosion prevention in mind.
- CHO-SHIELD 2000 series of electrically conductive coatings provide EMI shielding and corrosion protection for metal enclosures and flanges by providing a conductive moisture barrier that prevents corrosion. It does so by eliminating the electrolyte between the gasket and mating metal substrate.
- Within their specialty material family, CHO-BOND 1018 and 1019 electrically conductive sealants are both excellent options to provide a continuous electrical path within defensive and aerospace applications. CHO-BOND 1018 is a nickel-aluminum filled, two-component electrically conductive polythioether designed for use as a fillet, gap filler, and seam sealant on electrical enclosures. Engineered for harsh environments, CHO-BOND 1019 is a silver-plated aluminum-filled electrically conductive polythioether with excellent fluid and fuel resistance.
- CHO-SEAL reinforced conductive and non-conductive elastomer seals consist of a corrosion-resistant CHO-SEAL conductive or non-conductive elastomer base that is reinforced with a woven or knitted fabric material, or wire mesh. These seals are intended for use in airframe shielding applications or any other applications requiring a reinforced seal. CHO-SEAL 6502, 6503, 1298, 6460 are all excellent options to provide EMI shielding, lightning protection, HIRF protection and radar cross-section reduction by maintaining surface electrical continuity at joints, seams, and openings in airframes.
- Parker's Metalastic™ EXP-URE urethane-filled expanded aluminum gaskets provide an electrically conductive, fluid and pressure sealing solution for exterior mounted accessories. These gaskets ensure a conductive path for lightning strike protection and EMI shielding as well as environmental shielding for antennae on aircraft and various defense vehicles, protecting products from harsh chemicals while minimising galvanic corrosion.
Designed for your success
Parker Chomerics offers a broad catalogue of products that provide EMI shielding while minimising corrosion. All of these products are manufactured in North America in support of government procurement processes for defense and aerospace applications.