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Jet engines wouldn't work without high-performance coatings
Jet engines are one of the most breathtaking feats of engineering ever achieved.
But jet engines shouldn't be possible, says Ben Beake, director of materials research at Micro Materials, an equipment testing company in Wales.
“The air coming in is hotter than the melting point of the metal underneath – which is obviously not a good thing,” he explains, noting that this air reaches temperatures well above 1,000° c.
Jet engine designers have gotten around this problem by applying heat-resistant ceramic coatings to the engine blades. And now researchers are developing even tougher coatings that allow engines to run even hotter.
“If you raise the temperature higher, you will make huge savings on fuel and CO2,” says Dr Beake. By increasing the temperature by just about 30°C, you could save 8% on fuel, he estimates.
That's the power of coatings: they radically transform the functionality and capabilities of an underlying material. Few people realize how important they are, but these overlays and veneers can supercharge high-performance machines or ensure that expensive equipment survives the harshest environments.
Dr. Beake and his colleagues are on a mission to push coatings to their limits, to determine how robust or effective they really are. Her clients don't always get the results they want. He remembers telling a missile maker, “We broke your coating” a few years ago. “They left angry,” says Dr. Beake.
In addition to exposing coatings to high temperatures, Micro Materials also has a “pick” device, a small diamond stylus, that repeatedly taps a coating in random locations to test its durability.
Recently, the company worked with British company Teer Coatings to test a product that could be applied to satellite components, including gears and bearings used in various moving parts.
It's a tricky task, says the company's Xiaoling Zhang, because the coating must protect these components both before launch (when exposed to atmospheric humidity at ground level) and also in orbit, against dust particles and space radiation. However, she says the company has achieved the expected results.
But in addition to protecting spacecraft, the coatings could also prevent astronauts from getting sick.
Biofilms – accumulations of bacteria inside pipes – grow more quickly in low-gravity environments, which could pose a problem for water supplies or machines that move fluids on space stations or ships. future spaceships, for example.
“Biofilms are known to cause mechanical failures,” explains Kripa Varanasi of the Massachusetts Institute of Technology. “You don’t want this.”
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Professor Varanasi worked on super slippery surfaces
Professor Varanasi and his colleagues have developed a range of coatings that make surfaces slippery and therefore resistant to biofilm formation. Testing of one of these coatings in an experiment aboard the International Space Station found that it worked as expected.
The idea behind the coating is to mix a solid material and a lubricant. This is then sprayed onto the inside of a pipe or tube, making that interior surface extremely slippery.
Professor Varanasi has already made headlines by developing similar coatings for the inside of toothpaste sachets – so you can remove every last bit of toothpaste. He and his colleagues commercialized the technology through their spinoff company, LiquiGlide.
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The right coating could prevent molten aluminum from sticking to surfaces
Slipperiness is perhaps an underrated attribute. Nuria Espallargas of the Norwegian University of Science and Technology and colleagues developed a silicon carbide-based coating for equipment used in aluminum manufacturing or repair.
This is a sort of non-stick frying pan solution, meaning layers of molten aluminum don't get stuck on this expensive piece of equipment. How exactly this particular coating works, however, currently remains a mystery.
“To be honest, we don't really know how it works, the mechanism is unknown at the moment,” explains Professor Espallargas.
Nevertheless, the coating is commercially available through its spin-off company Seram Coatings. Atlas Machine and Supply, an American company that manufactures and repairs industrial machines, tested it.
“The real benefit lies in extending tool life and improving the quality of the products produced,” explains Jeremy Rydberg, director of innovation.
He says that without the coating, Atlas has to rebuild the roller tools she uses to work aluminum every two days. It costs $4.5 million a year. But the new coating means these tools last a full week, not just a few days, reducing rebuilding costs to about $1.3 million a year.
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Shipping is always interested in coatings that can keep hulls cleaner
Coatings can do amazing things, but they don't always work as expected, notes Andy Hopkinson, managing director of the Safinah Group, a company that is often called in to investigate when coatings malfunction.
“We're seeing a lot of problems in parking lots right now, where their passive fire protection system is peeling,” he says, referring to the fire-retardant paint sometimes applied to concrete structures.
And his company also discovered that coatings applied to commercial ships don't always prevent barnacles and other marine life from attaching to the hull. This problem, known as biofouling, increases friction, meaning the ship's engine has to work harder and consume more fuel.
Despite the availability of coatings that promise to be useful, shipowners do not always choose the right one for their vessel. This choice should depend on where the ship is sailing, how long it needs to be idle rather than moving, etc., says Dr. Hopkinson.
The cost of fixing issues like this can run into the thousands or even millions of dollars. “Typically, painting costs between 1 and 2% of the project. The problem is that when things go wrong, the costs become exponential,” says Hopkinson.
Researchers working in this area, however, say there are still many opportunities to improve coatings and develop new ones that could significantly improve the performance of machines or infrastructure in the future.
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