August 4, 2008

Method Grows Strong Fibers

By Raam Wong Journal Staff Writer

A Los Alamos scientist is perfecting a method for weaving and braiding some of the toughest materials known to man, to make fabrics and ropes that might one day be used in bulletproof vests or even to lift an elevator into space.

"Everyone needs stronger cable," Los Alamos National Laboratory scientist James Maxwell told the Journal in an interview.

The technology is named Laser-Weave for the bright laser beam that, when focused into a chamber of gas, can literally grow inorganic fibers while simultaneously intertwining them together.

The technique was honored this month on R&D Magazine's annual list of the 100 products representing "quantum leaps of technological improvement." It joined other winners like an improved airplane de-icer and the "Adaptive Airbag."

The Laser-Weave process begins by filling a small hyperbaric- pressure chamber with chemicals in gaseous phase. A laser is then focused onto a small surface area inside, forming a "hotspot" where the gas decomposes and leaves behind a solid fiber that can grow quite long in the direction of the laser beam.

"You can literally grow things out of thin air," Maxwell said.

The process, which those in the know call "laser chemical vapor deposition," has been around for quite a while. The difference with Maxwell's method is that he found that by shrinking down the laserheated surface to a pinprick, the fibers grow much faster.

"We've grown carbon fibers as fast as 13 centimeters per second before," Maxwell said. The scientist has even designed a spool outside the chamber that collects the fibers as they grow.

A diffractive optic can be used to create additional laser spots that produce numerous fibers at once. As the fibers grow along the line of the beams, the lasers are manipulated to intertwine the fibers. A super-strong cable, for instance, can be produced by rotating the optic as the fibers grow.

Laser-Weave also allows for more complex patterns of weaving and braiding than has been possible through traditional, mechanical methods.

"You can indeed make new, novel patterns," said Maxwell, who works in the lab's Applied Electromagnetics group.

Maxwell envisions using the Laser-Weave to turn very tough materials -- such as hafnium carbide, which has a melting point of more than 3,000 degrees Celsius -- into fiber. The resulting cloth or cable would be exceptionally strong and resistant to high temperatures.

Ultra-sturdy fabric could be used in rocket engine exhaust nozzles or installation in homes or toasters. And instead of coating tools with tungsten carbide, a manufacturer could form tungsten fibers in the shape of the tool and then infiltrate them with molten metal.

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