Sept. 19, 2002 — Ceramic materials — hard, strong and highly resistant to wear — are a desirable alternative to conventional materials in a wide variety of industrial applications. Yet, as anyone who has ever dropped a plate or mug knows, such hardness and strength comes at the expense of brittleness — not a very positive characteristic if you’re talking about a military application.
Enter the realm of nanostructured coatings. Since 1997, dozens of scientists have labored to create a nanostructured coating that is highly resistant to wear, erosion and corrosion and would be ductile enough for applications in which conventional ceramic coatings would fail.
The scientists, hailing from more than 20 organizations — military, academic and commercial — were led by Maurice Gell of the materials engineering department at the University of Connecticut. The effort is the brainchild of U.S. Navy visionaries who identified an opportunity to reduce life cycle costs and improve the maintainability of ships and their components.
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This combined effort culminated in the development, production and application of a nanoceramic composite coating made from alumina and titania, which Inframat Corp. — a privately held nanotechnology company founded in 1996 and based in Farmington, Conn., — now manufactures under the trade name Nanox 2613.
But Nanox is expensive. At an estimated $30 to $50 per pound, it can cost significantly more than competing products. According to Lawrence Kabacoff with the Office of Naval Research, who has been administering the research effort since its inception, in the short term “inroads into the civilian market generally have to be with people who have acute problems.” Such applications can be found mainly in environments that are especially aggressive in terms of wear or corrosion.
Conventional coatings are produced from particles that range from 0.1 to 1.0 microns in size. Such particles conduct heat well, completely melting during application and forming a homogeneous ceramic surface that is highly susceptible to cracking.
Nanostructured materials, with grain sizes smaller than 100 nanometers, do not conduct heat as well. As a result, when a nanostructured coating is sprayed on a substrate, the smaller grains do not all melt. This allows for the creation of a matrix that consists of large, pancake-like structures embedded in a weave of spherical nanoparticles. This microstructure allows the material to trap cracks rather than letting them propagate, key to the coating’s superior ductility and strength.
According to Gell, the alumina/titania nanoceramic exhibits a four- to six-fold improvement in wear, and a two-fold improvement in factor toughness and bond strength when compared to the conventional ceramic alternative.
The U.S. Navy is already using the nanostructured coating for a number of applications. For example, air intake and exhaust valves in submarines have been coated, saving $400,000 per ship — or an estimated $20 million over the next 10 years. Coating propulsion shafts on mine sweepers will result in a $1 million annual savings per ship. And naval engineers at the Naval Surface Warfare Center in Carderock, Md., have thus far managed to transition coatings for five other major vessel components, an effort estimated to result in an annual maintenance savings of $10 million.
Commercial applications abound, according to Kabacoff. “If you do something good for a pump on an aircraft carrier, then it’s good for any similar pump in the civilian world,” he said.
Nanox is being evaluated as a potential coating for ballast tanks, periscope shafts, valves and a variety of machinery components submersed in marine environments.
One mining company that leaches nickel and cobalt from low-grade ore has been testing Nanox coated ball valves. Such valves have to withstand a high-pressure slurry of crushed rock in an extremely acidic environment. Conventional valves last a few hours between refurbishings, but coated valves can survive for a couple of days.
In the automotive industry, the nanostructured coating is being tested for potential application to mufflers and exhaust manifolds. Oil and gas companies are evaluating it for use on screw pump rotors in commercial gas turbines and fuel feed pumps. And experts speak of numerous other applications in the printing, pulp and paper industries.
Inframat can now ship Nanox by the ton. John Burdick, Inframat’s executive vice president for corporate development would not say which companies are evaluating Inframat’s thermal spray coatings for use in their products, but he did say they were “household names and names you would know as Fortune 500 companies.” The company’s largest order to date has been for 1,000 pounds, an indication that customers are beginning to use the material for more than just experimental applications.