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CARBON NANOTUBES (CNT)

Carbon nanotubes (CNTs) are cylindrical nanostructures composed of carbon atoms arranged in a hexagonal structure. They are known for their exceptional mechanical, thermal, and electrical properties.

History

The concept of carbon nanotubes emerged in the late 20th century, following foundational research on carbon filaments conducted between the 1950s and 1970s, which suggested the possibility of tubular carbon structures. However, it was not until 1991 that Sumio Iijima, working at NEC in Japan, officially discovered carbon nanotubes. Using high-resolution electron microscopy, he revealed their distinctive cylindrical shape, marking a pivotal milestone in nanotechnology. By the 2000s, significant advances in synthesis techniques enabled CNTs to transition from experimental curiosities to practical materials, paving the way for their use in various industrial and research sectors. Today, carbon nanotubes have become indispensable in fields such as aerospace, electronics, and precision engineering, including innovative applications in horology to enhance performance and durability.

Production of Carbon Nanotubes

The production of CNTs relies on three main methods, each with its specific advantages and applications.

The most common method, Chemical Vapour Deposition (CVD), involves decomposing hydrocarbon gases such as methane at high temperatures over catalysts like iron or nickel. This process allows carbon atoms to self-assemble into tubular structures, making CVD a cost-effective option for large-scale production.

The arc discharge method, on the other hand, uses a high-intensity electric arc between graphite electrodes in an inert atmosphere, producing high-quality CNTs. However, its limited production scale restricts its use in mass industrial applications.

Finally, laser ablation involves vaporising a carbon target with a laser in a furnace. CNTs form as the vapour cools. While this technique produces nanotubes of exceptional quality, its high cost confines it to specialised applications.

Machining of Carbon Nanotubes

Working with carbon nanotubes presents several specific challenges requiring specialised techniques and equipment. Integrating CNTs into composites is essential, as pure CNTs are rarely used. They are generally combined with materials such as resins, ceramics, or metals to create composites. Precise machining of these composites demands rigorous control to preserve the integrity of the nanostructures. The extreme hardness of CNTs accelerates tool wear, necessitating the use of diamond-coated tools or carbide-tipped instruments to ensure precision and efficiency.

Additionally, while the excellent thermal conductivity of CNTs helps dissipate heat during machining, careful thermal management is essential to prevent deformation of adjacent materials.

Applications in Horology

The use of carbon nanotubes in horology remains anecdotal or purely experimental to this day. CNT balance springs were briefly commercialised. However, the high costs associated with their complex manufacturing processes, compared to the potential advantages of CNTs over traditional materials or other less expensive technical composites, likely explain their limited use in horology to date.