You certainly know that birds are enemies of jet engine turbine blades. But these jet engines have another nasty foe: sand. Even if the turbine blades are protected with thin layers of thermal barrier coatings (TBCs), they operate at very high temperatures. When a sand storm hits a blade, grains of sand melt and turn into glass. And this can have devastating effects on the duration of the blades. Now, engineers from Ohio State University (OSU) have developed a new coating made of 'fake diamonds to help jet engines take the heat.' The researchers have used zirconium dioxide -- commonly called zirconia, also known as synthetic diamonds -- to combat high-temperature corrosion. Even if the research results look promising, many years will pass before this technology might be widely adopted by the airline industry and the military. But read more...
You can see above on the left "conventional ceramic coating destroyed by molten glass. On the right, ceramic coating designed to resist molten glass (which is in a thin layer on top). The field of view of both images is about half a millimeter." (Credit: Aysegul Aygun and Nitin Padture, Ohio State University)
This research project has been led by Nitin Padture, professor of materials science and engineering at OSU, who is involved in other projects. For this particular project, he was helped by doctoral student Aysegul Aygun and former postdoctoral researcher Alexander Vasiliev, who is now at the Russian Academy of Sciences. Padture is also collaborating with Inframat Corporation, a nanotechnology company based in Farmington, Connecticut, which incidentally has a great phone number: 888-NANO-888.
As said Padture, "molten glass is one of the nastiest substances around. It will dissolve anything." So he developed new coating which forces the glass to absorb chemicals that will convert it into a harmless -- and even helpful -- ceramic. "The key, Padture said, is that the coating contains aluminum and titanium atoms hidden inside zirconia crystals. When the glass consumes the zirconia, it also consumes the aluminum and titanium. Once the glass accumulates enough of these elements, it changes from a molten material into a stable crystal, and it stops eating the ceramic."
In "Forget Diamonds -- Is Zirconia a Jet Engine's Best Friend?," Scientific American provides additional details. "In an effort to protect these coatings and ensure that turbine engines continue to operate properly, a team of Ohio State University engineers is testing a new formulation of zirconium dioxide, more commonly known as zirconia."
And here is how the OSU researchers have done. They've developed "a new coating method that changes the composition of the zirconia so that the molten glass cannot eat through and damage the turbines. "Our innovation is a new way of making the coating by adding aluminum and titanium to the zirconia crystals," says Padture, who has been studying thermal-barrier coatings for more than a decade. The aluminum and titanium turns molten glass into a stable crystal that poses no danger to the underlying ceramic surface."
This research work has been published in a recent issue of Acta Materialia, an Elsevier scientific journal, under the name "Novel thermal barrier coatings that are resistant to high-temperature attack by glassy deposits" (Volume 55, Issue 20, December 2007, Pages 6734-6745). Here are two links to the abstract and to the full paper (PDF format, 12 pages, 4.34 MB).
Sources: Ohio State University news release, March 17, 2008; Larry Greenemeier, Scientific American, March 21, 2008; and various websites
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