MANUFACTURE OF NANOTUBES ON AN INDUSTRIAL SCALE

Since their discovery in 1991, nanotubes have come up against difficult industrial realities. For the time being, only niche markets are concerned.This is undoubtedly one of the major discoveries of the last ten years: these tiny hollow fibers a few nanometers (billionth of a meter) in diameter and a few millimeters long focus the attention of thousands of researchers around the world. Their properties are truly exceptional: some carbon nanotubes are said to be a hundred times stronger than steel while being six times lighter. They deform at will (up to 30% of their initial size) without fracturing, are as good electrical conductors as copper, even semi-conductors like silicon in electronic chips depending on their morphology, and are also excellent conductors thermal...They were immediately imagined in almost all applications, from the reinforcement of composite material to the flat screen, via nanoelectronics, solar cells, fuel cells, artificial muscles... But for a new material makes its mark, it must bring new functionalities, if not be much more efficient than the one it replaces. However, for the moment, the characteristics of the products are still far from these theoretical properties.Nanotubes belong to a large family: their ancestors, "fullerenes", spherical molecules of 60 carbon atoms, were immediately hailed as a fundamental discovery (in 1985), crowned by the Nobel Prize in 1996. The first nanotubes _ a stack concentric of several tubes, henceforth baptized multiwalls _ were observed for the first time in 1991 by Sumio Iijima of NEC (Nippon Electric Company). In 1993, single-walled nanotubes were synthesized. They are the most efficient, but also the most difficult to produce, and therefore the most expensive: around 65 euros per gram. The main European producer is a French start-up created in 2001: Nanoledge, based in Montpellier, spun off from the CNRS.For the moment, the world production of nanotubes is around 100 tonnes per year, mainly multi-walled (99 tonnes), sold for a few thousand euros per kilogram by around forty producers, often from the world of research. However, it would take thousands of tons per year to reduce costs and ensure real industrial development. Today, the main producer is American (Hyperion Catalysis International, Cambridge), followed by CNI (Carbon Nanotechnologies Inc., Houston) or Showa Denko (Japan). The situation could quickly evolve towards significantly increased capacities. In particular, the French group Arkema (formerly Atofina), which has been supporting the development of a CNRS process for several years, has no hesitation in announcing shortly a "quality" production of several hundred tons per year, 50 to 100 euros per kilogram. Because quantity is not enough. "Currently, from one producer to another, the characteristics vary considerably depending on the degree of purity (actual percentage of nanotube), the perfection of the structure, the number of walls...", explains Kai Schierholz, technical director of Nanoledge, which integrates nanotubes, among other things, into composite materials. It is therefore difficult to ensure reproducible properties.

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