Nanotubes and the Pursuit of Applications
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Nanotubes and the Pursuit of Applications Walt A. de Heer Abstract A wide range of potential applications was suggested shortly after carbon nanotubes were discovered, including new super-strong materials, field-emission devices, hydrogen storage systems, novel electronic devices, and more. In this article, the actual advances in the technology of nanotubes over the last decade are examined. Particular attention is focused on current commercially viable applications and those with imminent commercial promise. The relatively large number of nanotube-related patents and nanotube-based startup companies stand in contrast to the relatively low output in commercial applications. The drive toward nanotube applications, in contrast to nanotube science, is investigated. Keywords: applications, carbon nanotubes.
Introduction In late 1991, Iijima1 announced his seminal high-resolution microscopy observations of carbon nanotubes produced in a 1 atm He arc using carbon electrodes. Iijima concentrated on the structural features of nanotubes: the helical structure that defined the shaft, the hemispherical fullerene-like caps, and the “Russian-doll” nesting of the various layers of multiwalled nanotubes. Although there had been earlier mentions of nanotubes,2,3 Iijima recognized their scientific importance and opened a new chapter in the science of nanographitic materials. The industrial importance of nanotubes had in fact been recognized earlier. In 1987, the first patent for a multiwalled nanotube was issued; this is a patent for the material itself.2 Shortly thereafter, a conducting plastic composite product based on nanotubes became commercially available. Compared with the proposed revolutionary applications that have been envisioned for nanotubes, this product is not very fascinating. Yet even now, it still represents the main commercial application of nanotubes. To put nanotubes in perspective, asproduced nanotube materials are, in some respects, similar to diamond. Not only are both made entirely of carbon, they both have exceptional properties. Diamond is the hardest material known and also has MRS BULLETIN/APRIL 2004
interesting optical properties. Like nanotubes, the quality of diamond varies considerably. Diamondlike films are highly defective, yet relatively easy to produce as durable coatings on a variety of substrates; industrial-quality diamond powders are readily produced and used as abrasives, while gem-quality diamonds are rare and extremely expensive. Diamond prices (see, for example, Reference 4) range from $1.50 USD per gram for industrial diamond powder to $1,000 per gram for gemquality diamonds; similarly, nanotube prices range from about $1 to $900 per gram. The most expensive nanotube material is research grade, with few or no structural defects, while the cheapest material has many defects, and the nanotubes within it may not even have hollow interiors. As with most materials, and as is obvious from the price range, the quality of nanotube material varies and depends on how it is produced. Some propos
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