U.S. Navy finding new applications for advances in nanotechnology.

• Author: Pappalardo, Joe

The Navy is finding a slew of applications for enhanced materials arising from advances in nanotechnology. Scientists believe these improved composites eventually will help the Navy lower the cost of procuring and maintaining ships.

"The applications run from the mundane to solutions to intractable problems," said Larry Kabacoff, program manager for nano-structured materials for the Office of Naval Research. "The return on investment of stone of these things is just staggering."

Many of the Navy projects use new processes to imbue aluminum oxide and titanium oxide into thin layers of ceramics, which produces substances that are tough, adhesive and pliable.

"The problem with current ceramic coatings is not that they wear down, but that they come off," he said, referring to the tendency of ceramics to crack and flake when damaged. "What is different is that [the new coatings] stay where you want them to."

The nano-ceramic coating is applied with a plasma spray, with miniscule particles of aluminum dust mixed into the spray and shot at high temperatures onto a surface. Some of the nano-sized particles group together upon hitting the surface, forming 30-micron sized balls that remain unmelted. These clumps are fixed under pressure by the contraction of the material when it rapidly cools. The mix of melted and unmelted portions makes a nano-composite that adds strength while keeping the chemistry of the original material.

This invisible interaction gives the product its resistance to cracking, Kabacoff explained. When the ceramic bends or is impacted, small cracks appeal, but run into the islands of unmelted, micron-size lumps. "It does crack, but the cracks run into regions of, micron-scale particles," Kabacoff said. "Cracking doesn't get very far in our material.

"When a crack reaches the interface in our material, the tensile stress at the crack tip is cancelled by the compressive stress in the material out in front of the tip," Kabacoff explained. "This is exactly how pre-stressed concrete works. Metal rods are compressed while the concrete hardens. When a load is put on the concrete, this stress just relaxes the pre-existing stress rather than adding new stress."

Kabacoff noted that these coatings also adhere to surfaces better than normal ceramics, and have the ability to deform along with whatever it is covering. This is a key point in weapons systems that are built to endure the abuses of the environment and war, such as a submarine...