Carbon nanotube 'paper' stronger than steel

Tallahassee, Fla. - Recent research using carbon nanotubes in place of conventional carbon fibers is revealing large gains in such critical material properties as tensile strength and electrical and thermal conductivity.

A striking example is a paper product that is ultrathin, electrically conducting and 10 times lighter than steel while still being 250 times stronger. Called buckypaper by its developer, the Florida Advanced Center for Composite Technologies (FAC2T), the material could enable the development of stronger ultralight aircraft or of lighter-weight yet more-effective body armor. It might also find a role in vehicle armor or the construction of stiff, durable yet paper-thin computer displays, researchers said.

"We will optimize and scale up buckypaper production and the technical development and demonstration of multifunctional applications of single-walled nanotube buckypapers for use in high-performance composite structures, sensors and devices," said FAC2T assistant director Frank Allen.

Buckypaper is created from carbon nanotubes, which can be magnetically aligned during fabrication using the National High Magnetic Field Laboratory's 25 Tesla supermagnet, located at Florida State University. Carbon nanotubes have a high aspect ratio, measuring nanometers wide but extending tens or hundreds of microns in length.

Carbon commonly forms into graphite, a flat sheet of carbon atoms bonded in a hexagonal, closely packed structure. Although the carbon-carbon bond is very strong, the two-dimensional sheets do not have much strength in any direction out of their plane. Carbon atoms can also bond into diamond, a three-dimensional crystal that is identical to crystalline silicon-a form that demonstrates the potential strength of carbon bonding.

FSU has four U.S. patents pending for buckypaper. Among the smorgasbord of applications slated for development using the material, FAC2T predicts buckypaper will prove applicable as a large-scale electron-field emitter for flat-panel displays, as a thermal conductor for superefficient heat sinks and as high-current protective film for the exteriors of airplanes. Such film would allow lightning strikes to flow around a plane and dissipate without damaging it.

FAC2T recently received $2.5 million in funding from the Army Research Lab and $1.2 million from the Air Force Office of Scientific Research.

"Our goal [for the Army and Air Force contracts] is toward technical development and demonstration of lightweight and multifunctional nanocomposites technologies for military applications. This will lead to making military vehicles lighter and stronger, to make transporting these vehicles to trouble areas faster and more efficient," said Allen.

In the 1980s a carbon atom arrangement called Carbon 60, or Buckminsterfullerene, was discovered that turned out to be twice as hard as diamond. The pattern of carbon atom links was found to be identical with the basic polyhedron that R. Buckminster Fuller used as a starting point for his geodesic dome-building system.

Supermagnet
Shortly after the discovery of Carbon 60, materials researchers discovered that the flat-sheet hexagonal form of carbon could also wrap around itself to create long hollow tubes. These nanotubes have a tensile strength 40 times greater than that of the carbon fibers currently used in aircraft. That strength is imparted to buckypaper when tangled clumps of nanotubes are straightened out by the supermagnet at Florida State's high-magnetic field laboratory.

"We are in pilot production of both randomly oriented and magnetically aligned buckypaper materials for various research and application demonstrations," Allen observed. "Fabrication involves dispersing nanotubes into a stable suspension and filtering the suspension to produce the buckypapers."

Meanwhile, in Japan, engineering professor Morinobu Endo at Shinshu University (Nagano, Japan) announced that he has been able to make buckypaper from double-walled, instead of single-walled, nanotubes. The tough material is flexible enough to be folded into a "paper" airplane. Endo is working toward a buckypaper material for flexible cables and electronic devices.

Buckypaper is the brainchild of professor Ben Wang, an industrial engineer at Florida State University. He also serves as the director of FAC2T, which aims to develop a range of high-performance composite materials and the processes to manufacture them.

"Our objective is to push the envelope to find out just how strong of a composite material we can make using buckypaper," Wang said. "In addition, we're focused on developing processes that will allow it to be mass-produced cheaply."

In addition to Wang, who is already well-known in the field of composite nanomaterials, another distinguished member of the FAC2T staff is Sir Harold Kroto, who was recently brought on board. Kroto shared (with two other scientists) the 1996 Nobel Prize in Chemistry for his discovery of Buckminster-fullerenes. It was Kroto, already steeped in Buckminster Fuller's geodesic dome theory, who made the intuitive leap that explained how 60 carbon atoms could arrange themselves in three dimensions. That discovery led to a whole family of revolutionary materials.

Kroto is now a professor with Florida State department of chemistry and biochemistry.