A military fighter pilot has much to focus on when in flight; namely fuel/range restrictions, inclement weather and enemy combatants. A lesser threat - although not benign - is lightning strikes which if not properly protected against can cause not only structural damage to the aircraft but also the internal electronics. 

Designing an aircraft is about trade-offs. Engineers choose composite materials that are lightweight, durable and aerodynamic to optimize in-flight performance; however, this leaves the outer skin of the aircraft electrically insulating and unable to protect from lightning strikes. 

A single lighting strike can contain as much as 200,000 amps, reaching very high temperatures. It is impossible for a pilot to anticipate and out-maneuver a strike so the strategy for lighting is not avoidance but mitigation. Here, the strategy lies in lining the outer skin of the aircraft with highly conductive materials, so the lightning has a conductive path where the energy dissipates.

For lightning strike protection, composite materials are treated after installation using a multi-layered approach. The primary layer providing lightning strike protection is a metallic mesh system integrated into the composite material. Highly conductive metals like copper and aluminum comprise this layer since they have high bulk conductivity and can dissipate high energy strikes quickly. 

Electrically Conductive Adhesives Bridge Gaps for a Continuous Conductive Path   

Electrically conductive adhesives (ECAs), specifically highly conductive compounds that use silver flake, supplement the conductive mesh layer, with localized application where gaps exist. These adhesives are highly conductive, lowering contact resistance where any discontinuity within the conductive layer may be. 

Specifically, conductive adhesive is applied along fastener interfaces, grounding points and to bond the mesh to the composite panels. In the unlikely event of a lightning strike, the electrical energy has now an uninterrupted conductive path for the current to flow. A continuous conductive path ensures no charge buildup along the aircraft frame, preventing excess heat and charring of the skin. 

Aside from its superior conductivity, silver is highly resistant to corrosion and can survive under repeated exposure to rain, mist and continuous freeze/thaw cycles from altitude changes. As an interface material, silver is ideal over other conductive fillers like copper or nickel since it does not corrode and galvanically couple with fastener materials. ECAs use an epoxy binder system which is highly durable and provides strong adhesion, providing reliable hold.

MG Chemicals Electrically Conductive Adhesives 

MG Chemicals has developed a full line of ECAs that use a highly engineered silver powder in an epoxy binder system. Available in both one and two-part systems, these ECAs provide robust adhesion to multiple substrates including wood, composites, plastics and metal. These adhesives are highly conductive and cure to form a rigid, high modulus solid. The typical operating temperature for an ECA ranges from -50 to 150°C meaning the adhesive can accommodate the temperature fluctuations common for aircraft.

The two-part systems are available in either a fast cure (8330D and 8331D) or slower cure (8330S and 8331S) for large volume productions. The 9410 is a one-part system that is turnkey and ideal for high-throughput projects where heat curing is not an issue. 

As aircraft design moves away from metallic sheeting to composite materials, a proper strategy for lightning strike protection relies now on conductive materials like ECAs. When properly coupled with a metallic mesh system, ECAs ensure the outer skin of the aircraft has sufficient conductivity to safely dissipate lightning strikes thus avoiding damage, downtime and costly repairs.

Read on our website: https://mgchemicals.com/tsLi

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MG Chemicals, a CADSI and Ontario Defence Association (ODA) member, manufactures specialty chemicals for electronics and defence applications from its facility in Burlington, Ontario. ​​