Upton, NY - Crab, shrimp, or lobster shells from the ocean plus corn from the earth are the key ingredients of a new "surf & turf" coating for metals. Developed by Brookhaven National Laboratory, the water-based coating protects metals from corrosion and moisture.
"And everything in this coating is 'green' - harmless to humans and the environment," said the inventor, Toshi Sugama, a chemist at Brookhaven Lab. This product, he says, is the latest payoff from the U.S. Department of Energy's years of support at Brookhaven for basic research on materials that are environmentally benign.
To create the base of the coating, a component called chitosan is extracted from crushed crab, shrimp, or lobster shells. "By using chitosan for the coating, we use the same substance that shellfish use for protection against the corrosive action of salt water," explained Sugama.
He added, however, that chitosan resists the action of water only when it is combined with certain other substances. Pure chitosan that has been extracted from shells is water soluble and does not stick well to metal.
To solve this problem, Sugama combined chitosan in water with another soluble "green" material that he had investigated previously - dextrine, which is found in cornstarch. When he heated this mixture in the right proportions, the dextrine's acidic properties acted on the chitosan to give a dense, moisture-resistant product that adheres to metals.
To coat a metal, it is dipped in the chitosan and dextrine solution several times, then heated to between 120 and 200 degrees centigrade, depending on how thickly it is covered. At the appropriate temperature, the coating changes its molecular formation and becomes firm and smooth, clinging well to aluminum and other metals.
The surf & turf coating protects metals from saltwater damage for twice as long as other coatings. Because of its potential in extending the life of aluminum in helicopters, this feature attracted additional funding for the research from the U.S. Army Research Office. "Recent tests show that the coating performs well in even in harsh, geothermal conditions," said Sugama. "Several companies are now evaluating the coating for industrial applications."
The coating will be renewable. "We are developing a way to spray it on metal surfaces and heat it with an infrared or ultraviolet lamp," said Sugama.
The finding was announced in the May 1999 issue of the Journal of Materials Science. Previous "green" research products from Sugama have included a high-performance cement, now in the public domain for use in geothermal wells, and a composite metal-and-ceramic coating to protect nickelchromium alloy used in smelting aluminum.
"You investigate materials' properties for years, then use that information to develop new applications," commented Sugama. "DOE's 15 years of support for our basic research into environmentally benign materials gave us the foundation that we build on to help industry."