Nanoparticulate zirconia (ZrO2) catalyzes both growth of single-wall and multiwall carbon nanotubes (CNTs) by thermal chemical vapor deposition (CVD) and graphitization of solid amorphous carbon
UPDATE: Prior non metal catalyst work (H/T to reader at cheaptubes): In a process patented by NASA Goddard is the ability to produce bundles of CNTs without using a metal catalyst. Because Goddard’s process does not use a metal catalyst, no metal particles need to be removed from the final product, yielding a significantly better product in terms of quality and purity at a dramatically lower cost.
Researchers at MIT have for the first time shown that nanotubes can grow without a metal catalyst. The researchers demonstrate that zirconium oxide, the same compound found in cubic zirconia "fake diamonds," can also grow nanotubes, but without the unwanted side effects of metal.
This can help make it easier to use carbon nanotubes to strengthen carbon fiber products. Carbon fiber is about 50,000 tons/year and carbon nanotubes are about 600-800 tons/year. Using some carbon nanotubes to increase the usefulness of carbon fiber helps to stretch out the currently still expensive and more rare carbon nanotubes. Non-metal catalyzed production also means less cancer causing worries for biomedical applications.
The implications of ditching metals in the production of carbon nanotubes are great. Historically, nanotubes have been grown with elements such as iron, gold and cobalt. But these can be toxic and cause problems in clean room environments. Moreover, the use of metals in nanotube synthesis makes it difficult to view the formation process using infrared spectroscopy, a challenge that has kept researchers in the dark about some of the aspects of nanotube growth.
One of the most exciting implications of the finding is that it means that carbon fiber and composites, used to make different types of crafts, could be strengthened by nanotubes. "Composites are durable, but fail under certain loading conditions, like when plywood flakes and splinters apart," says Stephen Steiner, an MIT graduate student and the study's first author. "But what if you could reinforce composites at the microlevel with nanotubes the way that rebar reinforces concrete in a building or a bridge? That's what we're trying to do to improve the mechanical properties and resistance to fracturing of carbon composites."
Steiner says the reason that planes like Airbus' A380 and Boeing's new 787 are made of only 40 percent composites and not 90 percent is because composites aren't strong enough for all parts of the craft. But if they were bolstered by nanotubes, then the planes could be made of more composites, which would make them lighter, and less expensive to fly because they wouldn't need as much fuel.
The findings are already impressing researchers in industry. "This innovation has far-reaching implications for commercial productions of carbon nanotubes," says David Lashmore, CTO of Nanocomp Technologies Inc., a company in Concord, N.H., that was not involved in the research. "It for the first time allows the use of a ceramic catalyst instead of a magnetic transition metal, some of which are carcinogenic.
Wardle suspects that more oxide-based catalysts will be found in the coming years. He and his team will focus on trying to understand the fundamental mechanisms of this type of nanotube growth and help to contribute more types of catalysts to the nanotube-growing arsenal. While the researchers don't have a timeline, they suspect that it would be easy to commercialize the process as it's simple, adaptable and, in many ways, more flexible than growth with metal catalysts.