Lasers Spin Nanotube Yarn

Lasers now have been used to create the first practical macroscopic yarns from boron nitride fibers, opening the door for an array of applications from solar cells to stronger body armor.

Researchers at NASA’s Langley Research Center, the Thomas Jefferson National Accelerator Facility and the National Institute of Aerospace have created a technique to synthesize high-quality boron-nitride nanotubes (BNNTs) that are highly crystalline and that have a small diameter. They also structurally contain few walls and are very long. Boron nitride is the white material found in clown makeup and face powder.

A yarn spun of boron-nitride nanotubes suspends a quarter. The nanotubes in this yarn were produced with a new technique discovered by researchers at NASA’s Langley Research Center, the US Department of Energy’s Thomas Jefferson National Accelerator Facility and the National Institute of Aerospace. The nanotubes are highly crystalline and have a small diameter. They also structurally contain few walls and are very long. (Photo: Jefferson Lab)

“Other labs can make really good nanotubes that are short or really crummy ones that are long. We’ve developed a technique that makes really good ones that are really long,” said Mike Smith, a staff scientist at Langley.

The synthesis technique, called the pressurized vapor/condenser (PVC) method, was developed with Jefferson Lab’s free-electron laser and later perfected using a commercial welding laser. In this technique, the laser beam strikes a target inside a chamber filled with nitrogen gas. The beam vaporizes the target, forming a plume of boron gas. A condenser, a cooled metal wire, is inserted into the boron plume. The condenser cools the boron vapor as it passes by, causing liquid boron droplets to form. These droplets combine with the nitrogen to self-assemble into BNNTs.

Researchers used the PVC method to produce the first high-quality BNNTs that are long enough to be spun into macroscopic yarn, in this case centimeters long. A cottonlike mass of nanotubes was finger-twisted into a yarn about 1 mm wide, indicating that the nanotubes themselves are about 1 mm long.

“They’re big and fluffy, textilelike,” said Kevin Jordan, a staff electrical engineer at Jefferson Lab. “This means that you can use commercial textile manufacturing and handling techniques to blend them into things like body armor and solar cells and other applications.”

VIDEO (click on image to play): Fibrils of boron-nitride nanotubes are formed through the pressurized vapor/condenser method. The nanotube fibrils are produced when the FEL laser beam strikes a target of pressed boron powder. The number indicates the laser power level in arbitrary units; about 1.5 kW in actuality. The target rotates to distribute the laser heat evenly. (Source: Jefferson Lab)

Transmission electron microscope (TEM) images showed that the nanotubes are very narrow, averaging a few microns in diameter. TEM images also revealed that the BNNTs tended to be few-walled, most commonly with two to five walls, although single-wall nanotubes also were present. Each wall is a layer of material, and fewer-walled nanotubes are the most sought after.

The researchers say the next step is to test the properties of the new boron-nitride nanotubes to determine the best potential uses for the new material. They also are attempting to improve and scale up the production process.

“Theory says these nanotubes have energy applications, medical applications and, obviously, aerospace applications,” Jordan said.

“Some of these things are going to be dead ends, and some are going to be worth pursuing, but we won’t know until we get material in people’s hands,” Smith said.

The research will be published in the Dec. 16 issue of the journal Nanotechnology. It also was presented today at the 2009 Materials Research Society Fall Meeting. The research was supported by the NASA Langley Creativity and Innovation Program, the NASA Subsonic Fixed Wing program, Jefferson Lab and the Commonwealth of Virginia. The experiments were hosted at Jefferson Lab.

For more information, visit: www.jlab.org