Graphene composite may keep wings ice-free

A thin coating of graphene nanoribbons in epoxy, developed by researchers at Rice University, has proven effective at melting ice on helicopter blades.

The coating by the Rice lab of chemist James Tour may be an effective, real-time de-icer for aircraft, wind turbines, transmission lines, and other surfaces exposed to winter weather, according to a new paper in the American Chemical Society journal ACS Applied Materials and Interfaces.

The lab melted centimeter- thick ice from a static helicopter rotor blade in a -4°F environment. When a small voltage was applied across the composite, the coating delivered heat – called Joule heating – to the surface, melting the ice.

The nanoribbons – produced commercially by unzipping nanotubes, a process also invented at Rice – are highly conductive. Rather than trying to produce large sheets of expensive graphene, the lab determined that nanoribbons in composites would interconnect and conduct electricity across the material with much lower loadings than traditionally needed.

The researchers fabricated a conductive composite of graphene nanoribbon (GNR) stacks and epoxy, which serve as a conductive additive. On average, the GNR stacks are 30nm thick, 250nm wide, and 30µm long.

Previous experiments showed how the nanoribbons in films could be used to de-ice radar domes and glass, since the films can be transparent.

“Applying this composite to wings could save time and money at airports where the glycol-based chemicals now used to de-ice aircraft are also an environmental concern,” Tour says.

In tests, nanoribbons were no more than 5% of the composite. Researchers, led by Rice graduate student Adul-Rahman Raji, spread a thin coat of the composite on a rotor blade segment supplied by a helicopter manufacturer. They then replaced the thermally conductive nickel abrasion sleeve used as a leading edge on rotor blades, and were able to heat the composite to more than 200°F.

For wings or blades in motion, the thin layer of water that forms first between the heated composite and the surface should be enough to loosen ice and allow it to fall off without having to melt completely, Tour says.

Researchers reported that the composite remained robust in temperatures up to nearly 600°F.

As a bonus, the coating may also help protect aircraft from lightning strikes and provide an extra layer of electromagnetic shielding Tour adds.

Co-authors of the paper are Rice undergraduates Tanvi Varadhachary and Kewang Nan; graduate student Tuo Wang; post-doctoral researchers Jian Lin and Yongsung Ji; alumni Yu Zhu of the University of Akron; Bostjan Genorio of the University of Ljubljana, Slovenia; and research scientist Carter Kittrell.

Tour is the T.T. and W.F. Chao Chair in chemistry as well as a professor of computer science and materials science and nanoengineering.

The Air Force Office of Scientific Research and Carson Helicopter supported the research.

Rice University

www.rice.edu

www.jmtour.com