Nanocoating protects building materials

By SCOTT R. BURNELL, UPI Science News  |  April 5, 2002 at 7:02 PM
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IDAHO FALLS, Idaho, April 5 (UPI) -- A composite material, made up of steel alloy clumps with only a few molecules per particle, could turn inexpensive, ordinary metals into durable building materials, researchers at the Idaho National Energy and Environment Laboratories said.

Daniel Branagan, a scientist at the national lab, studies the physical properties of materials such as metals. To improve the performance of today's alloys, he's turned to nanotechnology, where objects are measured in nanometers, thousands of times thinner than a human hair.

"In a conventional steel, you have basically one physical mechanism controlling both hardness and ductility. You can have a harder material, but it's less ductile," Branagan told United Press International. "Going on to the nanoscale, the different physical mechanisms allow you to overcome that dependence to a large extent."

Branagan's method involves creating alloys that solidify in a glass-like structure. Crushing the alloy creates a powder that, when applied at high temperature, bonds with other metals to form a very dense coating, with each particle about 50 nanometers in diameter. This process allows stronger atomic bonds in the material, the ultimate determinant of its strength, he said.

"The best steels out there commercially, they're at about 10 percent of (the theoretical best strength)," Branagan said. "By getting these very fine structures, we're able to overcome that and move it into the 40 to 45 percent level. You also have very good corrosion resistance at the nanoscale, because it's difficult for (corrosives to find a foothold)."

Tests have shown the "nanosteel" coatings are about 30 percent harder than regular steels, yet bend fairly easily, so they can be applied before or after a base metal is shaped. All these characteristics will help improve metal-based parts and building materials, Branagan said.

"If you have an application where you have mild corrosion, to overcome that you might go to a stainless steel at $10 or $12 a pound, instead of carbon steel at 50 cents a pound," Branagan said. "Now you can take a very cheap base material, apply (nanosteel) to protect the surface and therefore the whole part."

Melvyn Green, president of the Structural Engineers Association of California, told United Press International the procedure could be very useful as long as the parts or structures can still flex normally after the coating is applied. There are many situations where many kinds of steels don't last long, he said, such as in a plant that manufactures acidic chemicals.

"There may well be industrial facilities, not just industrial processes, where such coatings might offer protection at less cost than stainless or other steels," Green said.

Another metal that might benefit from nanosteel is aluminum, Branagan said -- its excellent strength-to-weight ratio is sought after in many applications, but its relative softness and vulnerability to corrosion often rule it out.

"Take aluminum, coat it with a (nanosteel) that essentially adds no weight, and you can totally change the characteristics of the whole system," Branagan said. Tests have shown the coatings will bond with aluminum.

Green cautioned that researchers and engineers should consider possible long-term interactions between aluminum and iron-based steels, since the two elements normally don't coexist very well.

Benefits from using nanosteel should become apparent even before large-scale uses are found, Branagan said.

"We're really talking about reducing total ownership costs. ... If your part lasts three times longer, your total reduction in cost would be significant," he said. "You can also change your design because of the revolutionary properties."

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