Rice lab overcomes supply issue in nanotube commercialization

Rice lab overcomes supply issue in nanotube commercialization
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BY JADE BOYD
Rice News Staff

Following four years of arduous work, chemists in Rice University’s Carbon Nanotechnology Laboratory (CNL) have created the first system that can continuously produce single-walled carbon nanotubes in bulk.

The refinement of the high-pressure carbon monoxide process, known as HiPco, is a watershed achievement in nanoscience because it eliminates the most significant bottleneck to nanotube commercialization: supply.

The first beneficiary of CNL’s HiPco efforts is NASA, which helped fund the development of the HiPco system under a five-year research program begun in 1998. In exchange for its support, NASA materials scientists have now received more than a pound of nanotubes, some 500 grams. That may not sound like much, but until a couple of years ago, all the single-walled nanotubes ever created worldwide totaled less than one pound.

“NASA was one of the first organizations to understand the tremendous potential of single-walled carbon nanotubes, and it was also one of the first to invest in that potential,” said Richard Smalley, CNL director and University Professor at Rice. “It’s fitting that they are the first to benefit from HiPco.”

Ultimately, NASA hopes to develop nanotube applications for space exploration. Because of their superior strength-to-weight ratio, single-walled nanotube composites may one day reduce the weight of spacecraft
by 50 percent or more compared to conventional materials.

Other space-exploration applications include energy storage, life support systems, thermal materials, nanoelectronics, nanosensors, electrostatic discharge materials and biomedical applications.

Nanotubes are cylindrical molecules of carbon atoms that have astounded scientists ever since they were discovered in 1991.

While some varieties of nanotubes contain multiple nested cylinders of carbon tubes, single-walled nanotubes are lighter, stronger and have superior mechanical and electrical properties than multi-walled varieties.

Stronger than steel, single-walled nanotubes are a family of more than 30 molecules. About one-third are metals and the rest are semiconductors. Researchers have used both nanotubes to make electronic components like molecular wiring and molecular transistors that are 100 times smaller than those found
in today’s most advanced microchips.

It is no exaggeration to say that engineers are considering using nanotubes in dozens of applications, but despite more than a decade of intense scientific interest, the supply of these intriguing molecules has always been limited.

Prior to the advent of HiPco, virtually all single-walled carbon nanotubes were produced in either carbon arcs or laser ovens at research laboratories.

Both processes are labor-intensive and time-consuming. Moreover, these batch processes yield just a few grams of nanotubes per day and cannot be scaled up to produce larger quantities needed for commercial applications.

Therein lies the promise of HiPco. By making nano-tubes plentiful and cheap — at least compared to today’s going rate of $500 per gram — HiPco will allow many more scientists to study carbon nanotubes, and it will pave the way for industry to start using them in products.

“Developing an affordable, reliable supply of single-walled carbon nanotubes is a crucial first step on the pathway toward revolutionary materials and systems for space exploration,” said Leonard L. Yowell, the carbon nanotube project manager at NASA’s Johnson Space Center. “With HiPco, NASA’s longstanding collaboration with Rice is paying off, not just for the agency’s materials scientists but for everyone pursuing research on single-walled carbon nanotubes.”

Carbon nanotubes are members of the family of carbon molecules known as fullerenes. The first fullerene discovered was Carbon 60, a soccer ball-shaped molecule of 60 carbon atoms that was discovered by Smalley and colleagues in 1985.

The Rice researchers noticed that the ball-shaped molecule looked like two conjoined geodesic domes, so the compound was named buckminsterfullerene in honor of geodesic dome inventor Buckminster Fuller.

The process used to create the first buckyballs at Rice in 1985 was carried out in a laser oven. The process involved using a laser to heat a rod of carbon graphite. The laser vaporized the carbon, creating a cloud of gaseous carbon atoms that reformed into buckyballs. In the early 1990s, researchers added trace metals to the graphite and discovered carbon nanotubes.

The metal atoms react with the carbon atoms, causing them to grow into long tubular structures containing thousands or even millions of atoms, rather than tight spheres containing 60 atoms.

Smalley’s research group, a part of Rice’s Center for Nanoscale Science and Technology, perfected a laser oven process for making single-walled nanotubes and began providing nanotubes to research groups at Rice, NASA and other institutions in the late 1990s under a program called Tubes@Rice. In fact, Rice helped NASA JSC set up its own laser ablation facility for nanotube production in 1997.

In 1998, NASA and Rice entered into a five-year program to collaborate on nanotube research. One thrust of that program — the development of a continuous flow process suitable for large-scale production of nanotubes — led to the development of HiPco.

In the HiPco process, the gaseous carbon atoms don’t come from vaporized graphite rods. Instead, they come from carbon monoxide gas, which is continuously pumped into a high-pressure reaction chamber and mixed with an industrial gas containing the necessary catalysts to sustain the chemical reactions that
create nanotubes.

The temperature and pressure conditions required in the HiPco process are common in industrial plants, and HiPco is both a less expensive and faster method of producing nanotubes than the laser-oven
method.

In 2000, Smalley and colleagues formed Houston-based Carbon Nanotechnologies Inc., a start-up company that holds exclusive worldwide license to the HiPco process and other Rice intellectual properties.