Jun 01 2015
The U.S. Naval Research Laboratory (NRL) has invented a special ceramic that looks like glass but is much harder, is tough like armor, and can be used on unmanned aerial vehicles, lenses, face shields and electronics protection.
Jas Sanghera, Ph.D, branch head of Optical Materials and Devices at the NRL, says the material, spinel, goes back to the 1960s when researchers attempted to make it synthetically.
“The material is found in nature as a mineral in small sizes, but for practical applications, one needs material larger than a centimeter, which is not found in nature,” Sanghera says. “Researchers tried to pack spinel powder into a denser material through a pressing process known as sintering, and if one does it right, the process gets rid of the empty space, the porosity, and the material becomes clear. We were able to do that.”
Sanghera says that NRL scientists were able to use a solid state process to heat the spinel to 1,500 degrees Centigrade, which is well below its melting point of 2,000 degrees Centigrade.
“We use a hot press that applies pressure to the material like a piston would to plungers inside a tube,” he points out. “We elevate the temperature, evacuate the air and the material is allowed to densify. The trick is to get rid of all the entrapped air in the material, and if you do that right, the result is a clear looking material.”
The resulting product is thinner than glass but much stronger, Sanghera notes. The NRL has produced spinel that is up to 11/2-inches thick, but is able to make thinner sheets of the material because most applications require a covering less than one inch thick, typically around a half-inch or less.
“This really is a transparent armor-like material,” Sanghera observes. “We have demonstrated the feasibility and transitioned this technology to industry to enable fabrication of larger finished products in the 25-inch square size.”
Sanghera says the transparent armor likely could be used for platform protection purposes.
“When you have cameras that operate in visible and infrared, it’s nice to have a rugged window in front of them,” he says. “Protecting cameras and sensors in military hardware is an important application. Wherever you see glass, polycarbonate or plastic, those can be areas for replacement by this material.”
Sanghera notes the strength of the transparent armor ranges by the size and shape of the finished material but that typically it is more than three-times stronger than glass of the same size.
“One of the areas of interest is replacing ballistic glass,” he says. “That’s a laminate of glass and plastic layers. The glass part of ballistic glass could be replaced with spinel, which would reduce the weight and thickness of the armor but give a greater strength.”
About the author: Alan M. Petrillo is a Tucson, Ariz., journalist who writes for national and regional magazines and newspapers. He’s the author of the historical mystery, Full Moon; the nonfiction work, Ice Hockey in the Desert; and his newest historical mystery, Asylum Lane, all available at www.amazon.com.