Sooty skies

Technology Quarterly Monitor

Aviation: A novel coating made of nanotubes offers a faster and more convenient alternative to chemicals for de-icing planes

DE-ICING an aeroplane is tedious. Just ask any passenger stuck in one while ground staff spray it with gallons of antifreeze. It is also important. Layers of ice can interfere with a wing’s aerodynamics, increasing drag and reducing lift, with potentially catastrophic consequences—hence the chemicals’ garish colours, meant to ensure that no nook or cranny is missed. De-icing can take as long as 40 minutes, and costs around $2,000 a pop.And sometimes, as Dawid Janas of Cambridge University found on a flight from his native Poland, it needs to be performed several times, because in harsh conditions the antifreeze itself can freeze if left to chill for long enough—as when awaiting the go-ahead for take-off. Now, though, Mr Janas, a materials scientist and aviation buff, thinks he has found a way to make life easier for passengers and airlines. It involves covering aircraft wings with a form of soot.

Not any old soot, mind you. Mr Janas creates his by pumping methane into a furnace heated to around 1,200°C. There, in the presence of an iron catalyst, the gas coalesces into a sticky substance akin to candyfloss, called an aerogel. When an iron poker is inserted into the furnace, the aerogel sticks to it. As the rod is retracted, it pulls out a thin filament, which is spun to create a film. Ten minutes later you get a sooty equivalent of an A4 piece of paper.

The film, about 10 microns thick, is composed of a mesh of carbon nanotubes, themselves just a few billionths of a metre across. Individual nanotubes are, famously, better conductors of electricity than even copper. In Mr Janas’s aerogel, however, they are no longer than 1mm each, with air in between them. That means the film, far from being a good conductor, exhibits high electrical resistance. Passing a current through it causes a near instantaneous rise in temperature.

Indeed, when Mr Janas compared his material with nichrome, the heating element of choice for applications from kettles to aeroplane wings (where it is used mainly for in-flight de-icing), he found that it heats up twice as fast using half as much energy as the metal alloy. It is also one ten-thousandth of the weight. The amount of film needed to cover the wings of a jumbo jet weighs just 80 grams.

Finally, whereas an A4 sheet of nichrome costs around $12,000, its carbon-film equivalent could be had for a hundredth of the price; probably less when the process is commercialised, as Mr Janas hopes it will be. Once installed, the heaters would be so cheap to run that they could be left on continuously at low power, to stop ice forming in the first place. And they last. A piece tested by Mr Janas retained its properties after being folded and unfolded 100,000 times.

Already a number of industries, though not yet aircraft-makers, have expressed an interest in the material. But if aviation does take to the stuff, the upshot will be more soot in the air—but of an entirely welcome variety.

found by Rhea